133 vehicles involved, 6 deaths. When something like this happens, there are usually multiple factors, as there were here. The accident started after a humped bridge over the railroad south of SH 183, so approaching drivers probably couldn't see the accident in time. I am wondering if this was the first icy bridge they encountered southbound since this was around the beginning of the area that got the freezing drizzle. Freezing drizzle showers were spotty and didn't hit all area equally, but they were generally southeast of a lime from Saginaw to Lewisville to McKinney. The drivers were all going around 70 MPH as they approached the accident, so they weren't being carful, even though the threat of freezing drizzle and rain was well advertised. Shows how clueless people really are. The accident happened in the toll lanes, which are maintained by North Texas Express, according to FOX4. There are several videos on Facebook of the accident happening. Police are conducting an investigation.
News Report: https://www.fox4news.com/news/multiple-injuries-from-icy-wreck-on-i-35w-in-fort-worth-involving-50-plus-vehicles (https://www.fox4news.com/news/multiple-injuries-from-icy-wreck-on-i-35w-in-fort-worth-involving-50-plus-vehicles)
GSV showing poor sight distance: https://www.fox4news.com/news/multiple-injuries-from-icy-wreck-on-i-35w-in-fort-worth-involving-50-plus-vehicles (https://www.fox4news.com/news/multiple-injuries-from-icy-wreck-on-i-35w-in-fort-worth-involving-50-plus-vehicles)
I pulled up the weather observations from Meacham Airport (KFTW), about 3 miles northwest of the crash site. They reported light freezing rain for only about 35 minutes, from approximately 1:35am until 2:10am. This was approximately 4 hours before the crashes began accumulating. But I know from personal experience (climatologically, Vermont is one of the most prone areas of the nation to freezing rain) that it doesn't take much to gum up the roads. And this is in a state with a mere fraction of the volume of traffic as the DFW metroplex.
Kind of sucks that it happened in the toll lanes, since there's a Jersey barrier on either side, so there's not really anywhere you can dodge to in order to avoid a collision...
Texas and it's stupid-ass preference for freeway humps over roads finally caught up with it. TxDOT better take a long, hard look at its design policies.
Quote from: TXtoNJ on February 12, 2021, 01:30:56 AM
Texas and it's stupid-ass preference for freeway humps over roads finally caught up with it. TxDOT better take a long, hard look at its design policies.
Here is my question what can they do prevent this from happening again? Maybe make the Express lanes for non-commercial vehicles? Make gates closing the express lanes in inclement weather? Reduce speed limit? There had already been chatter by many locals the lanes do not have safe design standards and can lead to chain reactions and you have nowhere to get off the road from the texpress lanes.
Nothing short of heating coils on all our highways will protect us from black ice.
Quote from: motorola870 on February 12, 2021, 03:23:16 AM
Quote from: TXtoNJ on February 12, 2021, 01:30:56 AM
Texas and it's stupid-ass preference for freeway humps over roads finally caught up with it. TxDOT better take a long, hard look at its design policies.
Here is my question what can they do prevent this from happening again? Maybe make the Express lanes for non-commercial vehicles? Make gates closing the express lanes in inclement weather? Reduce speed limit? There had already been chatter by many locals the lanes do not have safe design standards and can lead to chain reactions and you have nowhere to get off the road from the texpress lanes.
Well, supposedly TEXpress skimped on the sanding/salting/brining, clearly for cost reductions(hooray "free market"), so fixing that might be a good start.
I don't think blaming TxDOT is going to solve it, nor engineering some major system.
I have driven in many, many situations where the conditions declined so rapidly and in such a small area, that there is no system that could have stopped any of them.
In one situation in Ohio I got an anti-skid warning just before I exited and as I came around and under the bridge where I got the warning, 3 cars had already wiped out and the pile up was just beginning. It happens that fast at times.
So at times it not always the road either, the quality of the anti-skid system in the vehicle can make a difference.
In this circumstance in Ft Worth, anti-skid or anti-lock wouldn't have stopped you. There was a total loss of traction over several hundred yards which made these systems ineffective. Only chains or studs would have helped you and the rest of the road didn't require them.
In Oklahoma, I once drove through a thunderstorm when it was 24 degrees outside. It wreaked havoc as all the cars and trucks windshields all fogged over at the same time. Warm raindrops hitting cold windshields fogs them over faster than your defroster can keep up.
I ended up rolling the window down to see. But not everyone was so quick and ended up in the median.
That has to be the record for most vehicles involved in a single accident, right? If it is, then we should call Guinness and report it to them.
Quote from: Henry on February 12, 2021, 10:54:23 AM
That has to be the record for most vehicles involved in a single accident, right? If it is, then we should call Guinness and report it to them.
Nope, not even in the top 10. (https://en.wikipedia.org/wiki/Multiple-vehicle_collision), in September 2011, there was a 300 car pileup in Brazil.
Quote from: edwaleni on February 12, 2021, 10:19:14 AM
I don't think blaming TxDOT is going to solve it, nor engineering some major system.
I have driven in many, many situations where the conditions declined so rapidly and in such a small area, that there is no system that could have stopped any of them.
In one situation in Ohio I got an anti-skid warning just before I exited and as I came around and under the bridge where I got the warning, 3 cars had already wiped out and the pile up was just beginning. It happens that fast at times.
So at times it not always the road either, the quality of the anti-skid system in the vehicle can make a difference.
In this circumstance in Ft Worth, anti-skid or anti-lock wouldn't have stopped you. There was a total loss of traction over several hundred yards which made these systems ineffective. Only chains or studs would have helped you and the rest of the road didn't require them.
In Oklahoma, I once drove through a thunderstorm when it was 24 degrees outside. It wreaked havoc as all the cars and trucks windshields all fogged over at the same time. Warm raindrops hitting cold windshields fogs them over faster than your defroster can keep up.
I ended up rolling the window down to see. But not everyone was so quick and ended up in the median.
Closing the lanes with gates would help with this. They already have it for the I30 Texpress lanes between Arlington and Dallas. Also a lot of complaints about 18 wheelers being in the lanes impeding the flow of traffic as well in normal conditions. At this point banning 18 wheelers would be a smart move. Looking at the videos the 18 wheels compounded the wrecked cars. There needs to be standard operating procedures corrections.
Quote from: edwaleni on February 12, 2021, 10:19:14 AM
I don't think blaming TxDOT is going to solve it, nor engineering some major system.
I have driven in many, many situations where the conditions declined so rapidly and in such a small area, that there is no system that could have stopped any of them.
In one situation in Ohio I got an anti-skid warning just before I exited and as I came around and under the bridge where I got the warning, 3 cars had already wiped out and the pile up was just beginning. It happens that fast at times.
So at times it not always the road either, the quality of the anti-skid system in the vehicle can make a difference.
In this circumstance in Ft Worth, anti-skid or anti-lock wouldn't have stopped you. There was a total loss of traction over several hundred yards which made these systems ineffective. Only chains or studs would have helped you and the rest of the road didn't require them.
In Oklahoma, I once drove through a thunderstorm when it was 24 degrees outside. It wreaked havoc as all the cars and trucks windshields all fogged over at the same time. Warm raindrops hitting cold windshields fogs them over faster than your defroster can keep up.
I ended up rolling the window down to see. But not everyone was so quick and ended up in the median.
They absolutely have blame to share here. The accident happened because of a typical Texas "camelhump" situation, where there was a quick transition from bridge to grade to bridge, specifically done to reduce cost at the sacrifice of safety in adverse conditions.
I have watched traffic camera video of pileups and have seen how they can be seeded by just one or two vehicles wiping out in the traveled way, with involvement building up to over a hundred vehicles within a matter of minutes. YouTube has video (https://www.youtube.com/watch?v=Xb34A777o5A) of a February 2018 incident on I-35 near Ames, Iowa that is pretty classic--the first couple of vehicles wiped out due to loss of traction (ambient temperature was dropping), and that was all it took, in an area where drivers are accustomed to winter road conditions and with no structure involvement. (There were multiple injuries in this accident, but the lone fatality was a motorcoach driver who had a heart attack.)
In the Fort Worth incident, I tend to doubt the following will be fingered as proximate causes:
* Roadway on structure--This would seem to have been necessary to cross a railroad line and low-lying ground while maintaining good forward visibility.
* Barriers cutting off escape routes--It could be argued that the barriers actually helped, by keeping the pileup from overspilling into the general-purpose lanes.
* Not sanding and salting immediately before the crash--I'm not sure this would have helped since the precipitation was falling as rain, which washes off salt.
I wonder if outfitting the express lanes with variable speed limits and lowering the limit for adverse weather conditions would mitigate risk. I can see this being opposed by the express lane operator because of the associated costs of installation and operation, the prospect of poor compliance, and the repercussions for the pricing model.
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
I have watched traffic camera video of pileups and have seen how they can be seeded by just one or two vehicles wiping out in the traveled way, with involvement building up to over a hundred vehicles within a matter of minutes. YouTube has video (https://www.youtube.com/watch?v=Xb34A777o5A) of a February 2018 incident on I-35 near Ames, Iowa that is pretty classic--the first couple of vehicles wiped out due to loss of traction (ambient temperature was dropping), and that was all it took, in an area where drivers are accustomed to winter road conditions and with no structure involvement. (There were multiple injuries in this accident, but the lone fatality was a motorcoach driver who had a heart attack.)
In the Fort Worth incident, I tend to doubt the following will be fingered as proximate causes:
* Roadway on structure--This would seem to have been necessary to cross a railroad line and low-lying ground while maintaining good forward visibility.
* Barriers cutting off escape routes--It could be argued that the barriers actually helped, by keeping the pileup from overspilling into the general-purpose lanes.
* Not sanding and salting immediately before the crash--I'm not sure this would have helped since the precipitation was falling as rain, which washes off salt.
I wonder if outfitting the express lanes with variable speed limits and lowering the limit for adverse weather conditions would mitigate risk. I can see this being opposed by the express lane operator because of the associated costs of installation and operation, the prospect of poor compliance, and the repercussions for the pricing model.
I noticed on Google Maps that the speed limit for the toll lanes is posted at 75 mph just before the location of the crash. The videos show the semis approaching the pile of stopped cars at highway speeds. Now, maybe the drivers thought going 60 in a 75 meant they had slowed enough to be prudent, but clearly, that was still far too fast for the roadway conditions and visibility of traffic ahead of them due to the geometry of the road.
I have to think a lot of this boils down to excessive speed for the conditions. The videos show one semi scraping itself against the left jersey barrier, sparks flying, in a futile attempt to slow down before the impact. The FedEx semi struck a Toyota FJ Cruiser with enough force to drive it under a full-sized pickup truck and launch that truck end-over-end. Traffic may have had the chance to stop had it been moving 30 or 40 mph, or at least the damages and injuries wouldn't be nearly as severe.
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
I wonder if outfitting the express lanes with variable speed limits and lowering the limit for adverse weather conditions would mitigate risk. I can see this being opposed by the express lane operator because of the associated costs of installation and operation, the prospect of poor compliance, and the repercussions for the pricing model.
Variable speed limits would be an excellent inclusion for the express lanes in Texas. I think they are posted at 75, which seems too high as a permanent, non-lowerable limit. 75 is likely acceptable
most of the time, but certainly not all the time.
At the very least, variable limit signs (like those used by WSDOT) can display lane closed signs; this would have been helpful for traffic yesterday, as displaying multiple "X" symbols over the express lanes with accompanying VMS sign messaging (perhaps "incident ahead, prepare to stop") might have reduced the number of vehicles involved.
Quote from: Sani on February 12, 2021, 02:48:10 PM
I have to think a lot of this boils down to excessive speed for the conditions. The videos show one semi scraping itself against the left jersey barrier, sparks flying, in a futile attempt to slow down before the impact. The FedEx semi struck a Toyota FJ Cruiser with enough force to drive it under a full-sized pickup truck and launch that truck end-over-end. Traffic may have had the chance to stop had it been moving 30 or 40 mph, or at least the damages and injuries wouldn't be nearly as severe.
That particular crash (the semi hitting that Toyota) was one of the more haunting images from the whole incident. I mean, those cars were just demolished.
More alarming to me, from the scene, was (A) that trucks are allowed in the express lanes (such is forbidden here in WA), and (B) the speed trucks were going before crashing.
Here is the famous Wyoming I-80 pileup. Speed of the trucks in the conditions clearly played a role. Investigations found that many of the truck drivers were following each other with their stereos blasting not really looking ahead or watching the conditions closely.
Many died in this event.
Here is a walk through of the consequences.
The roadway agency reported application of brine prior to this event, possibly as early as Tuesday. Emergency responders reported no sand. Looks like they applied brine, and, thinking it would be enough, did not sand.
And, of course, the drivers were all going way too fast. As a weather and road enthusiast, it is unfathomable to me how clueless and negligent most drivers are. Of course many of us say drivers need to be re-educated, and after this, I'd say they need to add "It is the responsibility of the drivers to be aware of weather conditions, and make necessary adjustments to driving based on weather information".
Quote from: Brian556 on February 13, 2021, 12:05:42 AM
The roadway agency reported application of brine prior to this event, possibly as early as Tuesday. Emergency responders reported no sand. Looks like they applied brine, and, thinking it would be enough, did not sand.
And, of course, the drivers were all going way too fast. As a weather and road enthusiast, it is unfathomable to me how clueless and negligent most drivers are. Of course many of us say drivers need to be re-educated, and after this, I'd say they need to add "It is the responsibility of the drivers to be aware of weather conditions, and make necessary adjustments to driving based on weather information".
From the reports I have heard, the toll express lanes were treated with brine on Tuesday during the day about 36 hours before the pileup. I believe TXDOT treated the non-toll lanes both Tuesday and Wednesday. They were slippery in that area at the time of the accident but not as bad as the toll express lanes.
Excessive speed for the conditions, lack of timely road treatment, highway design, and commercial vehicle traffic on those toll express lanes were all contributing factors. Adding variable speed limit signs and other warning signage by itself probably wouldn't have eliminated the hazard. Lucky the death toll wasn't much higher given the circumstances.
Quote from: jakeroot on February 12, 2021, 03:06:07 PM
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
I wonder if outfitting the express lanes with variable speed limits and lowering the limit for adverse weather conditions would mitigate risk. I can see this being opposed by the express lane operator because of the associated costs of installation and operation, the prospect of poor compliance, and the repercussions for the pricing model.
Variable speed limits would be an excellent inclusion for the express lanes in Texas. I think they are posted at 75, which seems too high as a permanent, non-lowerable limit. 75 is likely acceptable most of the time, but certainly not all the time.
At the very least, variable limit signs (like those used by WSDOT) can display lane closed signs; this would have been helpful for traffic yesterday, as displaying multiple "X" symbols over the express lanes with accompanying VMS sign messaging (perhaps "incident ahead, prepare to stop") might have reduced the number of vehicles involved.
It's Texas. I'm not sure that a digital sign would be enough to cure the bravado of Texas drivers, especially in the DFW area which, unlike the parts of the state north and west, generally doesn't experience slick conditions with anywhere near the regularity that would cause drivers to get an intuitive understanding of icy conditions being a big deal.
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
In the Fort Worth incident, I tend to doubt the following will be fingered as proximate causes:
* Barriers cutting off escape routes--It could be argued that the barriers actually helped, by keeping the pileup from overspilling into the general-purpose lanes.
It may not be factored in as an official contributing factor (if for no other reason than how common dual Jersey barrier designs are in Texas, and the amount of money it would take to convert them to anything else). However, it's hard to ignore them as someone who is not writing an official statement on the accident. It's not hard to imagine a driver in the situation of having successfully stopped before collision or only struck a glancing blow, but thanks to the barriers has no way to leave the scene before getting struck themselves by other vehicles that were not so lucky.
I-35W seems to be bad luck for roadway disasters, whether in Texas or Minnesota. It was the I-35W bridge that collapsed over the Mississippi River in Minneapolis about a decade ago. If I were traveling through either place on I-35, I might consider taking I-35E.
Quote from: RoadWarrior56 on February 13, 2021, 08:34:18 AM
I-35W seems to be bad luck for roadway disasters, whether in Texas or Minnesota. It was the I-35W bridge that collapsed over the Mississippi River in Minneapolis about a decade ago. If I were traveling through either place on I-35, I might consider taking I-35E.
Solution: Get rid of lettered suffixes.
In Virginia the VMS signs definitely switch over to icy weather warnings when that is coming. Maryland's even have flashing beacons with theirs.
The northern half of the I-95 express lanes are set up for lane open/closed indicators and variable speed limits. The lane indicators are quite useful. But the variable speed limit capability is underused. I have never seen them changed for weather conditions, including when it was completely covered in snow and driving over 35 mph was ill advised. They only change them in conjunction with a disabled vehicle or accident blocking a lane.
Express lanes in the DC area do not allow tractor trailers, which were clearly a compounding factor in the DFW crash. Oddly I still see a few semis a month in the Express lanes over here and since State Police have dedicated patrols within the lanes who pull over 95% of them, it is surprising word hasn't gotten around that it is extremely unlikely you can travel these lanes in a semi and not get a hefty ticket.
Quote from: Scott5114 on February 13, 2021, 02:14:16 AMIt may not be factored in as an official contributing factor (if for no other reason than how common dual Jersey barrier designs are in Texas, and the amount of money it would take to convert them to anything else). However, it's hard to ignore them as someone who is not writing an official statement on the accident. It's not hard to imagine a driver in the situation of having successfully stopped before collision or only struck a glancing blow, but thanks to the barriers has no way to leave the scene before getting struck themselves by other vehicles that were not so lucky.
The standard advice (https://www.consumerreports.org/car-safety/how-to-protect-yourself-in-multicar-pileup/) for leaving a pileup is to stay in your car (where you are protected by the spaceframe) for a few minutes to give the point where additional collisions are occurring a chance to recede from your position, and then--if you choose to get out--move toward and past the point of the initial collision before you try to find a lateral route off the highway.
At least part of the I-35W crash was on a viaduct (https://www.google.com/maps/@32.7875083,-97.3212845,3a,75y,309.21h,83.63t/data=!3m7!1e1!3m5!1sirCBYFaaNZStnC2nU7qCFw!2e0!6s%2F%2Fgeo3.ggpht.com%2Fcbk%3Fpanoid%3DirCBYFaaNZStnC2nU7qCFw%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D9.298181%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192!5m1!1e1) that appears to have a concrete deck without a polymer overlay (example (https://www.google.com/maps/@37.7086288,-97.4100388,3a,75y,117.42h,83.67t/data=!3m6!1e1!3m4!1sG-SMOk8PtOIZjLKUhOl-BA!2e0!7i13312!8i6656)). As preservation of surface friction is one of the main reasons for using such surface treatments, I wonder if the accident might have been mitigated (if not prevented altogether) if one had been present.
As regards variable speed limits, I hypothesize compliance would be higher if the imposition of a reduced limit were related to inputs that indicate definitely the driving surface is freezing (e.g., high humidity, precipitation falling initially as rain, temperatures dropping--all of which were present immediately before the I-35W pileup) and coupled with a VMS message such as "Roadway Icing Up." Nowadays RWIS sensors that report pavement temperature are more or less standard ITS components, and when they are installed and working, they take a lot of the guesswork out of assessing whether the driving surface is wet and freezing. (In Kansas, KDOT runs a RWIS dashboard (http://rwis.ksdot.org/) I have used, in conjunction with the state 511 website, to decide whether to risk winter travel.)
This happens all the time in the more experienced snow driving north. So I do not understand how a overpass can cause a pile up. It was black ice, when the drivers saw the tail lights it was too late. They were already on the black ice and the grade heading south is down hill also.
I am more interested to see if the private company treated the road.
Quote from: longhorn on February 13, 2021, 06:07:42 PM
This happens all the time in the more experienced snow driving north. So I do not understand how a overpass can cause a pile up. It was black ice, when the drivers saw the tail lights it was too late. They were already on the black ice and the grade heading south is down hill also.
I am more interested to see if the private company treated the road.
Well there were a lot of contributing factors. This section of road being completed about 3 years ago and there is even more questions to be asked such as why did TXDOT deem it necessary to double the length of the viaduct from the original configuration. I remember the construction.
A lot of the motorists who were involved in the Fort Worth pile-up on I-35W were completely screwed before they realized it. They were driving along in what they thought were acceptable driving conditions, and likely pushing their speeds a bit in order to get ahead of the morning rush. They were driving fast in the express lanes and couldn't see what was ahead of them. Once the first couple motorists crashed out they were trapped on the main lanes thanks to the concrete Jersey barriers. If this pile up had happened on one of those really stupid single lane express lanes in the DFW area the pile up would have had a telescope effect with every car collapsing into each other like an old fashioned telescope tube. With the scale of this accident, 2 lanes of width didn't help much.
It's worth mentioning this Polar Vortex event has been all over the news for the past week. On Wednesday morning, a day prior to this pile-up in Fort Worth the freezing rain and black ice was wreaking havoc up here in Oklahoma. I-44 in Lawton was shut down for hours due to a truck jack-knifing on the Westbound lanes going into the Cache Road interchange. We had dozens of accidents all over town. I damned near did the splits slipping on my front porch as I stepped out the door to go to work! I think I-40 in Oklahoma City was shut down for a time due to a pile up there. There were hundreds of accidents all over the state, including a few fatal accidents.
That should have given the folks down in the DFW area a clue of what was in store for them the next morning.
Quote from: longhornSo I do not understand how a overpass can cause a pile up.
Bridges are the first roadways that cake-up with black ice. It's very likely that motorists going Southbound on I-35W were driving just fine in the express lanes
right until they hit that long bridge going over Watauga Road and a rail line.I-35W goes under the TX-183/28th Street exit and then immediately goes into a climb to get over the next street and that rail line. Freeway main lanes built at grade take longer to accumulate ice. There was a little bit of freezing rain that fell past midnight. But the significant freezing rain in that area didn't begin until about 6:00am Thursday morning -just 30 minutes prior to the pile-up.
Quote from: Scott5114I'm not sure that a digital sign would be enough to cure the bravado of Texas drivers, especially in the DFW area which, unlike the parts of the state north and west, generally doesn't experience slick conditions with anywhere near the regularity that would cause drivers to get an intuitive understanding of icy conditions being a big deal.
Few other cities can match drivers in DFW for Kamikaze-like speeding, swift lane changes and all sorts of other aggressive driving behaviors. New Orleans is pretty bad. But, yeah, it's very common for motorists in DFW to not take heed of road conditions. I've seen pile-ups happen in Dallas in the middle of Summer due to only rain-slicked pavement from an isolated shower.
Quote from: Bobby5280 on February 13, 2021, 07:55:18 PM
A lot of the motorists who were involved in the Fort Worth pile-up on I-35W were completely screwed before they realized it. They were driving along in what they thought were acceptable driving conditions, and likely pushing their speeds a bit in order to get ahead of the morning rush. They were driving fast in the express lanes and couldn't see what was ahead of them. Once the first couple motorists crashed out they were trapped on the main lanes thanks to the concrete Jersey barriers. If this pile up had happened on one of those really stupid single lane express lanes in the DFW area the pile up would have had a telescope effect with every car collapsing into each other like an old fashioned telescope tube. With the scale of this accident, 2 lanes of width didn't help much.
It's worth mentioning this Polar Vortex event has been all over the news for the past week. On Wednesday morning, a day prior to this pile-up in Fort Worth the freezing rain and black ice was wreaking havoc up here in Oklahoma. I-44 in Lawton was shut down for hours due to a truck jack-knifing on the Westbound lanes going into the Cache Road interchange. We had dozens of accidents all over town. I damned near did the splits slipping on my front porch as I stepped out the door to go to work! I think I-40 in Oklahoma City was shut down for a time due to a pile up there. There were hundreds of accidents all over the state, including a few fatal accidents. That should have given the folks down in the DFW area a clue of what was in store for them the next morning.
Quote from: longhornSo I do not understand how a overpass can cause a pile up.
Bridges are the first roadways that cake-up with black ice. It's very likely that motorists going Southbound on I-35W were driving just fine in the express lanes right until they hit that long bridge going over Watauga Road and a rail line.
I-35W goes under the TX-183/28th Street exit and then immediately goes into a climb to get over the next street and that rail line. Freeway main lanes built at grade take longer to accumulate ice. There was a little bit of freezing rain that fell past midnight. But the significant freezing rain in that area didn't begin until about 6:00am Thursday morning -just 30 minutes prior to the pile-up.
Quote from: Scott5114I'm not sure that a digital sign would be enough to cure the bravado of Texas drivers, especially in the DFW area which, unlike the parts of the state north and west, generally doesn't experience slick conditions with anywhere near the regularity that would cause drivers to get an intuitive understanding of icy conditions being a big deal.
Few other cities can match drivers in DFW for Kamikaze-like speeding, swift lane changes and all sorts of other aggressive driving behaviors. New Orleans is pretty bad. But, yeah, it's very common for motorists in DFW to not take heed of road conditions. I've seen pile-ups happen in Dallas in the middle of Summer due to only rain-slicked pavement from an isolated shower.
Hopefully they make changes after the investigation the public's interest and not TEXPRESS including the possibility that 18 wheelers are prohibited from the lanes. Even before the crash the TEXPRESS system has some interesting choices on lane configurations. Such as left hand entrances and exits to the Express lanes. A lot of modern interchanges are eliminating left hand entrances and exits.
Quote from: longhorn on February 13, 2021, 06:07:42 PM
So I do not understand how a overpass can cause a pile up.
Because northern drivers are used to snowy and icy conditions.
Quote from: 1 on February 13, 2021, 08:16:08 PM
Quote from: longhorn on February 13, 2021, 06:07:42 PM
So I do not understand how a overpass can cause a pile up.
Because northern drivers are used to snowy and icy conditions.
That and my dad taught me & my brother that if an overpass could have ice on it, when you come up to it, let off your accelerator and coast over the bridge. Once you're clear, then you can use your accelerator once again. Of course, this doesn't work for those super long ones, but does for the majority of the super short ones on Interstates.
Quote from: rickmastfan67 on February 13, 2021, 08:18:46 PM
Quote from: 1 on February 13, 2021, 08:16:08 PM
Quote from: longhorn on February 13, 2021, 06:07:42 PM
So I do not understand how a overpass can cause a pile up.
Because northern drivers are used to snowy and icy conditions.
That and my dad taught me & my brother that if an overpass could have ice on it, when you come up to it, let off your accelerator and coast over the bridge. Once you're clear, then you can use your accelerator once again. Of course, this doesn't work for those super long ones, but does for the majority of the super short ones on Interstates.
Yes, and I've experienced it firsthand several times. The worst part of I-135 going north here in Wichita is actually after it stops being the Canal Route and has become ground-level again. It's just north of that point, where it goes over the railroad and Hydraulic/29th Street. The reason it's worse is because, while the Canal Route itself is long and straight and level, that bridge has a slight curve and a slight incline. Any ice there, and your drive wheels do funny things that they don't do on the Canal Route itself.
I also remember the time I was driving OK at 50-55 mph coming south down I-135, with some snow and ice but nothing out of the ordinary. Bridges, curves, no problem, just slow down a little bit and all is well. Then I came around the bend at 17th Street, where it becomes the Canal Route, and there were two wrecks on the viaduct, and my car spun out to 90 degrees before I could regain control. Sometimes one bridge is fine but another is not. That's just the way winter weather driving is. People in this part of the country get a lot more experience learning these things than people in Dallas.
My approach to driving on ice is informed by my background in physics. The key is to keep net friction demand as low as possible. Here are a few key facts:
* Most tires start skidding when friction demand gets to about 65%-70% of gravitational acceleration on dry pavement. Smooth ice reduces this friction capacity by at least a factor of 10.
* Most sets of geometric design standards in use in advanced industrialized countries cap friction demand at about 25%. This means that if you are moving at the design speed, the maximum lateral acceleration you should experience on the least forgiving curve allowable under the standards is about 25%. Often (not always) the "hands-off" speed on curves--i.e., the speed at which there is no lateral acceleration at all and you can track through the curve without touching the steering wheel--is a consistent fraction (usually around 60%) of the design speed. This often comes into play when negotiating curved ramps on structure, since going too slow can result in a vehicle skidding toward the inside of the curve since it does not have enough speed to oppose the superelevation.
* Because we in the US are a weird, exceptionalist country, we use the same set of values for horizontal curve radii at a given design speed regardless of the maximum superelevation (emax) used in a particular area. 8% is a pretty common value for emax, but it can go as low as 4% in areas susceptible to frequent icing. It helps to have at least an intuitive understanding of the superelevation provided in your area so you can choose your speed accordingly--lower maximum superelevation values translate to reduced tolerance for speeds above the hands-off speed.
* The distance required to execute a given change in speed is proportional to the square of initial speed. The relevant equation is vf2 = vi2 + 2ad. This means that relatively modest reductions in your speed can greatly improve your ability to stop when traction is compromised. But, as a practical matter, maintaining a margin of safety is a mixture of driving more slowly than usual and also leaving wider space cushions. This is especially relevant for trips that occur during peak commute periods, when headways are typically shorter (important point: it is not possible to achieve the usual maximum throughput of 2000 vehicles per lane per hour while maintaining the minimum two-second following distance that is usually recommended for safety). When a storm comes through in the afternoon on a workday, it is not worth it to risk a car that costs a minimum of $20,000 to replace new just to get home at close to the usual time--I'd simply plan to leave later, even if it is hours later, and keep sleeping gear at the office during the winter.
Quote from: J N Winkler on February 14, 2021, 12:53:20 PM
This often comes into play when negotiating curved ramps on structure, since going too slow can result in a vehicle skidding toward the inside of the curve since it does not have enough speed to oppose the superelevation.
This is also handy knowledge to have if you're navigating a muddy unpaved road and come upon a banked curve. Too slow, and you'll find yourself at the bottom of the inside, unable to get back out again.
Quote from: J N Winkler on February 14, 2021, 12:53:20 PM
When a storm comes through in the afternoon on a workday, it is not worth it to risk a car that costs a minimum of $20,000 to replace new just to get home at close to the usual time--I'd simply plan to leave later, even if it is hours later, and keep sleeping gear at the office during the winter.
What do you do if the storm comes through in the morning? Not go in?
Quote from: Bobby5280 on February 13, 2021, 07:55:18 PM
Quote from: longhornSo I do not understand how a overpass can cause a pile up.
Bridges are the first roadways that cake-up with black ice. It's very likely that motorists going Southbound on I-35W were driving just fine in the express lanes right until they hit that long bridge going over Watauga Road and a rail line.
The reason bridges ice first, by the way, is because they are exposed to the cold from both top and bottom. Regular roadways are only exposed to cold air from above, with (relatively) warmer ground below.
We're getting into the worst of the winter storm here in Oklahoma now. The Turner Turnpike was shut down in both directions due to a pile-up earlier today.
https://www.koco.com/article/turner-turnpike-closed-in-both-directions-in-east-oklahoma-city/35502317#
I've measured 8 inches of snow so far in my back yard here in Lawton, and the temperature topped out at 8°F. We'll be below zero here by Monday morning and maybe close to -10°F by early Tuesday morning.
If every single heat wave is held up as a reason to prevent climate change, can't we hold this mess up as a reason to encourage it?
Quote from: kernals12 on February 14, 2021, 08:07:17 PM
If every single heat wave is held up as a reason to prevent climate change, can't we hold this mess up as a reason to encourage it?
Quote from: kphoger on February 04, 2021, 05:07:33 PM
I realize full well that there's still plenty of time left before Spring, but... It hasn't dropped below 16 degrees at all this year in Wichita. If we don't have a decent cold snap, I have a feeling the bugs are going to be out in force when the weather warms up later.
Hopefully, that will come next week.
Houston's cold snap will get rid of the bugs this year.
Quote from: kernals12 on February 14, 2021, 08:07:17 PM
If every single heat wave is held up as a reason to prevent climate change, can't we hold this mess up as a reason to encourage it?
No.
Quote from: kernals12 on February 14, 2021, 08:07:17 PM
If every single heat wave is held up as a reason to prevent climate change, can't we hold this mess up as a reason to encourage it?
Sure.
Quote from: 1 on February 14, 2021, 08:09:59 PM
Houston's cold snap will get rid of the bugs this year.
I'll let you know if that turns out to be the case. I hope so, but part of me thinks they'll stick around anyways. :)
If mosquitoes last the winter in the North, they will in the South...
Quote from: Rothman on February 15, 2021, 09:33:39 AM
If mosquitoes last the winter in the North, they will in the South...
They... don't last the winter in the north?
Quote from: Rothman on February 15, 2021, 09:33:39 AM
If mosquitoes last the winter in the North, they will in the South...
They aren't the only bugs. Ant problems, for example, are a lot worse if we don't experience a good cold snap.
Quote from: CoreySamson on February 14, 2021, 10:49:48 PM
Quote from: 1 on February 14, 2021, 08:09:59 PM
Houston's cold snap will get rid of the bugs this year.
I'll let you know if that turns out to be the case. I hope so, but part of me thinks they'll stick around anyways. :)
I would think they'd come back in the spring/summer. This weather might be enough to kill them off for a couple of months, but they'll be back.
This evil cold spell isn't going to do squat about bugs in Oklahoma. We're still in the dead of winter. Maybe if we had a serious cold snap in April that would make a difference on the bug population. But not now.
First there was the 133-Vehicle Accident in Fort Worth. Now the state has widespread power blackouts. I wonder what will happen to Texas next?
It appears this crash was caused by freezing drizzle. That is one of the hardest things to guard against. If it happened in a small localized area, it's almost impossible to get there at the appropriate time. When I do my snow work, I'm driving on a stretch of 10 miles of roadway. Doesn't matter how many times I go up and down, if I'm in one area and something occurs five miles away, it's going to take me at least 10 to 15 minutes to get to it most likely.
Brine is utilized to assist at the beginning of snow and ice. Once it gets wet it quickly loses its effectiveness. If it rained before the freezing drizzle occurred, it does no good as its washed away. If a freezing drizzle lasted for a period of time, the brine helped at first, then its effectiveness disminished quickly.
Salting roads before a storm generally doesn't help. Salt is like trash on a roadway. As traffic goes by it it gets swept off a dry Road. Salting a sriveway or parking lot may be okay, because traffic is moving at very slow speeds. Traffic on highways, at highway speeds, just blows it off.
And remember, this is Texas. Not only are motorists not used to such conditions, Texas doesn't have the large amounts of equipment needed on roadways for hazardous conditions. Even in other areas of the country that sees snow and ice often, the fact is trucks break down, and equipment malfunctions. I can be going down the road salting roadways, look back, and suddenly see that no salt is being spread. Now I have to figure out why that is, and once resolved, do I keep going or circle back? A lot of this work is manual or visual...I don't have stuff in my truck to notify me of every issue.
Treating roads for snow & ice is one of the most difficult things any transportation department has to face. Just a small area left untreated can cause issues like what we saw down in Texas. Also, when crews are plowing roads the plows are pushing against the immense amounts of snow, grinding against curbs, going over manhole covers that may not be flush with the ground, and utilizing equipment in freezing weather. It all makes fighting winter weather conditions an extremely difficult task.
I don't believe anyone else on these forums works with a transportation department in the area of plowing and salting roads. If you ever have the chance, try it for a season. You'll realize it's a very difficult job, especially with a demanding travelling public that feels roads should never be in less but perfect conditions at all times.
Quote from: jeffandnicole on February 15, 2021, 10:44:41 PM
It appears this crash was caused by freezing drizzle. That is one of the hardest things to guard against. If it happened in a small localized area, it's almost impossible to get there at the appropriate time. When I do my snow work, I'm driving on a stretch of 10 miles of roadway. Doesn't matter how many times I go up and down, if I'm in one area and something occurs five miles away, it's going to take me at least 10 to 15 minutes to get to it most likely.
Brine is utilized to assist at the beginning of snow and ice. Once it gets wet it quickly loses its effectiveness. If it rained before the freezing drizzle occurred, it does no good as its washed away. If a freezing drizzle lasted for a period of time, the brine helped at first, then its effectiveness disminished quickly.
Salting roads before a storm generally doesn't help. Salt is like trash on a roadway. As traffic goes by it it gets swept off a dry Road. Salting a sriveway or parking lot may be okay, because traffic is moving at very slow speeds. Traffic on highways, at highway speeds, just blows it off.
And remember, this is Texas. Not only are motorists not used to such conditions, Texas doesn't have the large amounts of equipment needed on roadways for hazardous conditions. Even in other areas of the country that sees snow and ice often, the fact is trucks break down, and equipment malfunctions. I can be going down the road salting roadways, look back, and suddenly see that no salt is being spread. Now I have to figure out why that is, and once resolved, do I keep going or circle back? A lot of this work is manual or visual...I don't have stuff in my truck to notify me of every issue.
Treating roads for snow & ice is one of the most difficult things any transportation department has to face. Just a small area left untreated can cause issues like what we saw down in Texas. Also, when crews are plowing roads the plows are pushing against the immense amounts of snow, grinding against curbs, going over manhole covers that may not be flush with the ground, and utilizing equipment in freezing weather. It all makes fighting winter weather conditions an extremely difficult task.
I don't believe anyone else on these forums works with a transportation department in the area of plowing and salting roads. If you ever have the chance, try it for a season. You'll realize it's a very difficult job, especially with a demanding travelling public that feels roads should never be in less but perfect conditions at all times.
Yes that is all true but locals have said for a while the lanes are not safe due to the fact they only have one shoulder and no exit in case of a wreck. Not to mention we have 1 travel lane wide express lanes on the eastern side of the metro. Don't be surprised if there is a push to ban big rigs off of the lanes. Its almost meme territory anyone you speak with talks about how they are literally sandwiched in between the jersey barriers. I also wonder if Texpress will see a drop in usage after the wreck from drivers that are cautious and don't feel comfortable driving in such narrow lane configurations.
Wouldn't the lack of Jersey barriers only have created the conditions for head-on collisions instead?
Quote from: Scott5114 on February 13, 2021, 02:14:16 AM
Quote from: jakeroot on February 12, 2021, 03:06:07 PM
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
I wonder if outfitting the express lanes with variable speed limits and lowering the limit for adverse weather conditions would mitigate risk. I can see this being opposed by the express lane operator because of the associated costs of installation and operation, the prospect of poor compliance, and the repercussions for the pricing model.
Variable speed limits would be an excellent inclusion for the express lanes in Texas. I think they are posted at 75, which seems too high as a permanent, non-lowerable limit. 75 is likely acceptable most of the time, but certainly not all the time.
At the very least, variable limit signs (like those used by WSDOT) can display lane closed signs; this would have been helpful for traffic yesterday, as displaying multiple "X" symbols over the express lanes with accompanying VMS sign messaging (perhaps "incident ahead, prepare to stop") might have reduced the number of vehicles involved.
It's Texas. I'm not sure that a digital sign would be enough to cure the bravado of Texas drivers, especially in the DFW area which, unlike the parts of the state north and west, generally doesn't experience slick conditions with anywhere near the regularity that would cause drivers to get an intuitive understanding of icy conditions being a big deal.
Quote from: J N Winkler on February 12, 2021, 02:32:49 PM
In the Fort Worth incident, I tend to doubt the following will be fingered as proximate causes:
* Barriers cutting off escape routes--It could be argued that the barriers actually helped, by keeping the pileup from overspilling into the general-purpose lanes.
It may not be factored in as an official contributing factor (if for no other reason than how common dual Jersey barrier designs are in Texas, and the amount of money it would take to convert them to anything else). However, it's hard to ignore them as someone who is not writing an official statement on the accident. It's not hard to imagine a driver in the situation of having successfully stopped before collision or only struck a glancing blow, but thanks to the barriers has no way to leave the scene before getting struck themselves by other vehicles that were not so lucky.
Yes everyone mentioning a lower speed limit would have help obviously hasn't driven this exact stretch of highway south of Ft. Worth where the speed limit is 60-65 mph and everyone is easily doing 90. It's no joke at all, they are literally making you feel like you are sitting still when you are also speeding at 70. I am not talking about 1 or 2 cars, but everyone on I-35W.
Quote from: kphoger on February 13, 2021, 09:21:19 PM
Quote from: rickmastfan67 on February 13, 2021, 08:18:46 PM
Quote from: 1 on February 13, 2021, 08:16:08 PM
Quote from: longhorn on February 13, 2021, 06:07:42 PM
So I do not understand how a overpass can cause a pile up.
Because northern drivers are used to snowy and icy conditions.
That and my dad taught me & my brother that if an overpass could have ice on it, when you come up to it, let off your accelerator and coast over the bridge. Once you're clear, then you can use your accelerator once again. Of course, this doesn't work for those super long ones, but does for the majority of the super short ones on Interstates.
Yes, and I've experienced it firsthand several times. The worst part of I-135 going north here in Wichita is actually after it stops being the Canal Route and has become ground-level again. It's just north of that point, where it goes over the railroad and Hydraulic/29th Street. The reason it's worse is because, while the Canal Route itself is long and straight and level, that bridge has a slight curve and a slight incline. Any ice there, and your drive wheels do funny things that they don't do on the Canal Route itself.
I also remember the time I was driving OK at 50-55 mph coming south down I-135, with some snow and ice but nothing out of the ordinary. Bridges, curves, no problem, just slow down a little bit and all is well. Then I came around the bend at 17th Street, where it becomes the Canal Route, and there were two wrecks on the viaduct, and my car spun out to 90 degrees before I could regain control. Sometimes one bridge is fine but another is not. That's just the way winter weather driving is. People in this part of the country get a lot more experience learning these things than people in Dallas.
And that's why folks up north have studded snow tires, particularly on rear-wheel drive vehicles. A set of chains also comes in handy, particularly for deep snow.
This is black ice. Snow melts quickly in Texas then refreezes. It is then black ice. What happens in the overpasses are humps. You come from a longish clear section where you are at clear road speed, you go over one hump (that has no visability over) and there is the traffic that has crashed going up the next one. CRASH. CRASH , CRASH
Even northern transplants struggle here. Driving in icy conditions in Texas is way different than where i am today in Colorado.
Quote from: bwana39 on February 16, 2021, 12:22:29 PM
Even northern transplants struggle here. Driving in icy conditions in Texas is way different than where i am today in Colorado.
Yep. Even driving here in Wichita is more challenging than where I grew up in northwestern Kansas, even though we get less snow here. Ice is a whole different beast.
Quote from: ethanhopkin14 on February 16, 2021, 10:28:51 AM
Yes everyone mentioning a lower speed limit would have help obviously hasn't driven this exact stretch of highway south of Ft. Worth where the speed limit is 60-65 mph and everyone is easily doing 90. It's no joke at all, they are literally making you feel like you are sitting still when you are also speeding at 70. I am not talking about 1 or 2 cars, but everyone on I-35W.
I would hope such speeds wouldn't be common sights on mornings like those where the pileup occurred. Below freezing temperatures and the chance for black ice mean that drivers should have been driving perhaps much more cautiously than they were. I can understand northerners being a bit less cautious, but southerners aren't used to this crap, so why was everyone hauling ass like nothing was going on? You'd think they'd be a bit more timid.
The point of lower limits during certain occasions (remember: variable limits, not a permanent lowering of the limit) would be to warn drivers of an upcoming incident. Drivers had very little warning along those express lanes of the upcoming crash. If
signs like these (https://goo.gl/maps/kSFwnvknSng8NyvE6) were in place, drivers could have been alerted to the crash. The per-lane signs could have shown a very low limit (25 or 35?) or even a red "X", and then the accompanying VMS could have displayed "CRASH AHEAD PREPARE TO STOP". This wouldn't have necessarily prevented any more collisions, but it certainly would have cut down on the number of drivers going full speed into each other.
Quote from: jakeroot on February 16, 2021, 03:31:35 PM
Quote from: ethanhopkin14 on February 16, 2021, 10:28:51 AM
Yes everyone mentioning a lower speed limit would have help obviously hasn't driven this exact stretch of highway south of Ft. Worth where the speed limit is 60-65 mph and everyone is easily doing 90. It's no joke at all, they are literally making you feel like you are sitting still when you are also speeding at 70. I am not talking about 1 or 2 cars, but everyone on I-35W.
I would hope such speeds wouldn't be common sights on mornings like those where the pileup occurred. Below freezing temperatures and the chance for black ice mean that drivers should have been driving perhaps much more cautiously than they were. I can understand northerners being a bit less cautious, but southerners aren't used to this crap, so why was everyone hauling ass like nothing was going on? You'd think they'd be a bit more timid.
The point of lower limits during certain occasions (remember: variable limits, not a permanent lowering of the limit) would be to warn drivers of an upcoming incident. Drivers had very little warning along those express lanes of the upcoming crash. If signs like these (https://goo.gl/maps/kSFwnvknSng8NyvE6) were in place, drivers could have been alerted to the crash. The per-lane signs could have shown a very low limit (25 or 35?) or even a red "X", and then the accompanying VMS could have displayed "CRASH AHEAD PREPARE TO STOP". This wouldn't have necessarily prevented any more collisions, but it certainly would have cut down on the number of drivers going full speed into each other.
Texas has those systems. Outside of San Antonio, its a lot of fancy signs to tell you not to drink because it's Super Bowl weekend. I hope this gets them to use the system the way it's supposed to be used.
Quote from: kphogerWouldn't the lack of Jersey barriers only have created the conditions for head-on collisions instead?
I don't think anyone would suggest removing the concrete barrier separating the North and South directions of traffic. But there are pro and con reasons for and against removing a concrete barrier separating Southbound toll/express lanes and Southbound general purpose lanes. I've seen some configurations where the only thing "separating" premium express lanes from general purpose lanes is a double set of road stripes.
IMHO, TX DOT and various other toll road agencies should shut down express lanes when icy road conditions are fixing to develop. I agree with others about having dynamic speed limits, at least in major cities. I also think most of the current traffic advisory signs installed overhead absolutely suck. Most of them look like they date back to the early 1990's. They could install full matrix LED boards capable of showing critical information in a far more effective manner.
Quote from: jakeroot on February 16, 2021, 03:31:35 PM
Quote from: ethanhopkin14 on February 16, 2021, 10:28:51 AM
Yes everyone mentioning a lower speed limit would have help obviously hasn't driven this exact stretch of highway south of Ft. Worth where the speed limit is 60-65 mph and everyone is easily doing 90. It's no joke at all, they are literally making you feel like you are sitting still when you are also speeding at 70. I am not talking about 1 or 2 cars, but everyone on I-35W.
I would hope such speeds wouldn't be common sights on mornings like those where the pileup occurred. Below freezing temperatures and the chance for black ice mean that drivers should have been driving perhaps much more cautiously than they were. I can understand northerners being a bit less cautious, but southerners aren't used to this crap, so why was everyone hauling ass like nothing was going on? You'd think they'd be a bit more timid.
The point of lower limits during certain occasions (remember: variable limits, not a permanent lowering of the limit) would be to warn drivers of an upcoming incident. Drivers had very little warning along those express lanes of the upcoming crash. If signs like these (https://goo.gl/maps/kSFwnvknSng8NyvE6) were in place, drivers could have been alerted to the crash. The per-lane signs could have shown a very low limit (25 or 35?) or even a red "X", and then the accompanying VMS could have displayed "CRASH AHEAD PREPARE TO STOP". This wouldn't have necessarily prevented any more collisions, but it certainly would have cut down on the number of drivers going full speed into each other.
Texas has LOTS of the VMS. They tend to have generic messages. There are location specific data on them at times, but outside of metro Houston, I don't recall ever seeing real-time data. The wreck ahead signs are in use around Houston.
The dynamic speed limits might be helpful, but probably not within tyhe purview of TXDOT and perhaps would complicate the rules of the (emissions) attainment zone agreements.
The Jersey barriers may have complicated this wreck, but any type of barrier would have created a similar outcome. The Jersey barriers save more lives in a given year than they create,
Quote from: bwana39 on February 17, 2021, 09:32:39 AM
The Jersey barriers save more lives in a given year than they create
Quote from: bwana39 on February 17, 2021, 09:32:39 AM
Texas has LOTS of the VMS. They tend to have generic messages. There are location specific data on them at times, but outside of metro Houston, I don't recall ever seeing real-time data. The wreck ahead signs are in use around Houston.
Quote from: ethanhopkin14 on February 16, 2021, 04:17:17 PM
Texas has those systems. Outside of San Antonio, its a lot of fancy signs to tell you not to drink because it's Super Bowl weekend. I hope this gets them to use the system the way it's supposed to be used.
The VMS signs are just one part of how variable limits work. The variable per-lane limits would show which lanes are closed, open, suggested speeds; the VMS sign would tell drivers
why, even if something more or less generic like "reduced speed zone" -- it's better than lowering the limits but without any signage to explain why.
Example from Seattle (https://goo.gl/maps/GF6qFiNUtbYvDeHY7) showing how they work in tandem. There's also these
mini displays (https://goo.gl/maps/wdEXRWVoXPX4R4k79) that display shorter helpful messages or speed limit signs. They can
also displays arrows and X's (https://goo.gl/maps/uUxmuQobJpFT69uQ7) to close lanes or warn of caution.
Here's a page (https://wsdot.wa.gov/travel/operations-services/active-traffic-management/how-atdm-symbols-work) where they show all the symbols and messages that you can see in use around the Seattle region.
Easy response. Pre-emptive salting and sand.
If the temp is going to get within a few degrees of freezing in the forecast, your pour salt.
If it is going to get below 15 degrees, you use calcium chloride with sand, not sodium chloride.
Do it proactively in the event of, not wait until. If you wait, then its too late.
Quote from: jeffandnicole on February 15, 2021, 10:44:41 PM
Brine is utilized to assist at the beginning of snow and ice. Once it gets wet it quickly loses its effectiveness. If it rained before the freezing drizzle occurred, it does no good as its washed away. If a freezing drizzle lasted for a period of time, the brine helped at first, then its effectiveness disminished quickly.
Salting roads before a storm generally doesn't help. Salt is like trash on a roadway. As traffic goes by it it gets swept off a dry Road. Salting a sriveway or parking lot may be okay, because traffic is moving at very slow speeds. Traffic on highways, at highway speeds, just blows it off.
Quote from: edwaleni on February 17, 2021, 01:15:31 PM
Easy response. Pre-emptive salting and sand.
If the temp is going to get within a few degrees of freezing in the forecast, your pour salt.
If it is going to get below 15 degrees, you use calcium chloride with sand, not sodium chloride.
Do it proactively in the event of, not wait until. If you wait, then its too late.
jeffandnicole, who actually works in snow plowing, seems to disagree with you.
Quote from: jakeroot on February 17, 2021, 01:06:12 PM
Quote from: bwana39 on February 17, 2021, 09:32:39 AM
Texas has LOTS of the VMS. They tend to have generic messages. There are location specific data on them at times, but outside of metro Houston, I don't recall ever seeing real-time data. The wreck ahead signs are in use around Houston.
Quote from: ethanhopkin14 on February 16, 2021, 04:17:17 PM
Texas has those systems. Outside of San Antonio, its a lot of fancy signs to tell you not to drink because it's Super Bowl weekend. I hope this gets them to use the system the way it's supposed to be used.
The VMS signs are just one part of how variable limits work. The variable per-lane limits would show which lanes are closed, open, suggested speeds; the VMS sign would tell drivers why, even if something more or less generic like "reduced speed zone" -- it's better than lowering the limits but without any signage to explain why.
Example from Seattle (https://goo.gl/maps/GF6qFiNUtbYvDeHY7) showing how they work in tandem. There's also these mini displays (https://goo.gl/maps/wdEXRWVoXPX4R4k79) that display shorter helpful messages or speed limit signs. They can also displays arrows and X's (https://goo.gl/maps/uUxmuQobJpFT69uQ7) to close lanes or warn of caution.
Here's a page (https://wsdot.wa.gov/travel/operations-services/active-traffic-management/how-atdm-symbols-work) where they show all the symbols and messages that you can see in use around the Seattle region.
Yes, but the key element here would be for them to actually work instead of informing us how many people have died that year on the roads in Texas. The system is in place, but it is never put into motion the way it was designed. It actually annoys me there are so many VMSes in the state with either nothing on them or some stupid generic jingle about slowing down on them, not because of traffic, but how to avoid a ticket. Also, those digital arrows above lanes are all over the state and are just off. I don't understand why you install a system and never use it.
A side note, this all happened within minutes. How would information get relayed to the system? Does it have to be called in? Is it somehow automated by scanning roadways for slowdowns?
Quote from: edwaleni on February 17, 2021, 01:15:31 PM
Easy response. Pre-emptive salting and sand.
If the temp is going to get within a few degrees of freezing in the forecast, your pour salt.
If it is going to get below 15 degrees, you use calcium chloride with sand, not sodium chloride.
Do it proactively in the event of, not wait until. If you wait, then its too late.
We don't have these resources down here. It is seen as a waste of money for the event it happens maybe once every five years. Same reason our houses down here don't have insulated or heated piping. There is no point putting that expensive system in the houses here just so we can use them for a day and a half every five years.
Quote from: ethanhopkin14 on February 17, 2021, 01:22:23 PM
Yes, but the key element here would be for them to actually work instead of informing us how many people have died that year on the roads in Texas. The system is in place, but it is never put into motion the way it was designed. It actually annoys me there are so many VMSes in the state with either nothing on them or some stupid generic jingle about slowing down on them, not because of traffic, but how to avoid a ticket. Also, those digital arrows above lanes are all over the state and are just off. I don't understand why you install a system and never use it.
A side note, this all happened within minutes. How would information get relayed to the system? Does it have to be called in? Is it somehow automated by scanning roadways for slowdowns?
Well yes, they need to be active and working. There's really no point to them if they just sit off half the time. The regular VMS displays should be off when not in use (those generic jingles are a waste of electricity, and drivers ultimately just ignore them), but the speed limit signs really should always be on, unless the traffic is really light.
The system in WA is monitored 24/7 by a traffic management center, but it's largely automated using
loop detectors (https://goo.gl/maps/pcy98jPcf2WLbhg66). It's true that this did happen quite fast, but I think it would have been caught in some way. Or at the very least, a lowered limit could have been put in place with "ice" warnings on the VMS displays.
Quote from: kphoger on February 17, 2021, 01:19:47 PM
Quote from: jeffandnicole on February 15, 2021, 10:44:41 PM
Brine is utilized to assist at the beginning of snow and ice. Once it gets wet it quickly loses its effectiveness. If it rained before the freezing drizzle occurred, it does no good as its washed away. If a freezing drizzle lasted for a period of time, the brine helped at first, then its effectiveness disminished quickly.
Salting roads before a storm generally doesn't help. Salt is like trash on a roadway. As traffic goes by it it gets swept off a dry Road. Salting a sriveway or parking lot may be okay, because traffic is moving at very slow speeds. Traffic on highways, at highway speeds, just blows it off.
Quote from: edwaleni on February 17, 2021, 01:15:31 PM
Easy response. Pre-emptive salting and sand.
If the temp is going to get within a few degrees of freezing in the forecast, your pour salt.
If it is going to get below 15 degrees, you use calcium chloride with sand, not sodium chloride.
Do it proactively in the event of, not wait until. If you wait, then its too late.
jeffandnicole, who actually works in snow plowing, seems to disagree with you.
Oklahoma has been experimenting with spraying on a brine mixture before bad weather. The theory is it should stay in place and keep the roads clearer longer. I'll have to look and see if they have published results. Oklahoma State University has also experimented with a self deicing bridge deck. I believe it has heating elements in the concrete.
https://hvac.okstate.edu/sites/default/files/HPCC_Bridge_Deck_Deicing.pdf
They spray with brine before bad weather in Wichita too. But not if it's going to be raining first.
Quote from: J N Winkler on February 14, 2021, 12:53:20 PM
* Because we in the US are a weird, exceptionalist country, we use the same set of values for horizontal curve radii at a given design speed regardless of the maximum superelevation (emax) used in a particular area. 8% is a pretty common value for emax, but it can go as low as 4% in areas susceptible to frequent icing. It helps to have at least an intuitive understanding of the superelevation provided in your area so you can choose your speed accordingly--lower maximum superelevation values translate to reduced tolerance for speeds above the hands-off speed.
I have no idea where you got this idea from, but it's absolutely not true. The AASHTO design guidelines definitely have separate tables of minimum radii for different values of max. superelevation, see below screenshot from the table of contents of "A Policy on Geometric Design of Highways and Streets, 7th Edition" (not going to post the actual tables since AASHTO seems to be fairly protective of their copyright).
(https://i.imgur.com/mXl7dtx.png)
If there is some state, county, city, or other agency not using these standards, that's on them. And I'd be quite surprised given the potential liability.
I think what he's saying that if you're using the maximum, which you usually are, it doesn't matter what the maximum is. If you're using a constant value, the maximum does matter, but it shouldn't (6% superelevation has the same physical properties whether the maximum you're allowed to use is 6% or 8%, but the two tables give different values, while 6% with 6% maximum corresponds to 8% with 8% maximum).
Quote from: stevashe on February 24, 2021, 05:39:00 PMQuote from: J N Winkler on February 14, 2021, 12:53:20 PM
* Because we in the US are a weird, exceptionalist country, we use the same set of values for horizontal curve radii at a given design speed regardless of the maximum superelevation (emax) used in a particular area. 8% is a pretty common value for emax, but it can go as low as 4% in areas susceptible to frequent icing. It helps to have at least an intuitive understanding of the superelevation provided in your area so you can choose your speed accordingly--lower maximum superelevation values translate to reduced tolerance for speeds above the hands-off speed.
I have no idea where you got this idea from, but it's absolutely not true. The AASHTO design guidelines definitely have separate tables of minimum radii for different values of max. superelevation, see below screenshot from the table of contents of "A Policy on Geometric Design of Highways and Streets, 7th Edition" (not going to post the actual tables since AASHTO seems to be fairly protective of their copyright).
It is true, as I think you can verify for yourself by looking at the nomographs for different values of
emax. For an 80 MPH design speed, for example, a 6000 ft curve would receive superelevation of 4.3% for
emax = 8% and 4% for
emax = 6%. (I'm working with the sixth edition of the Green Book, but I assume yours is similar.)
I wasn't actually talking about minimum radii, which--as you say--are different for different values of
emax at the same design speed.
Another way of expressing this point is that the same combination of curve radius and superelevation can correspond to different design speeds depending on the
emax chosen for design. This creates issues with design consistency, as discussed in a 1999 FHWA report (https://www.fhwa.dot.gov/publications/research/safety/ihsdm/99171/) prepared as part of the research program that led to the Interactive Highway Safety Design Model (which has been used by a number of agencies to assess proposed alignments for new highways).
Quote from: stevashe on February 24, 2021, 05:39:00 PMIf there is some state, county, city, or other agency not using these standards, that's on them. And I'd be quite surprised given the potential liability.
I am personally not aware of any cases (or at least any that have been litigated in any recent decade) that hinged entirely on design criteria for horizontal alignment.
There are some states, such as California, that have their own design standards for horizontal and vertical alignment. From past conversations with practitioners, I think the concern that comes into play is ensuring the state-specific standards stay above a floor defined by whatever edition of the Green Book FHWA has adopted for federal-aid highways. (There was a mini-controversy in 2004 when AASHTO dropped the "dead dog" criterion for forward sight distance, resulting in lower
k-values being allowed for summit curves. There was talk of amending state DOT highway design manuals to mandate continued use of the older, more conservative values.)
As regards the Fort Worth pileup, the Green Book has interesting things to say about friction coefficients on ice. They can range from 20% down to 5%, the lower limit corresponding to black ice forming on wet roadways as they drop just under the freezing point--exactly the conditions that came into play in this incident.