I searched for an existing topic on this but was unable to find any, though I also don't know if I'm using the correct terminology.
The scenario is such:
A ramp with two lanes (or more) merges into a multi-laned roadway. The right lane(s) on the merging ramp gets its own lane while the left does not and must immediately merge.
Examples:
The worst I've seen is in San Francisco, at 101/80, which is so bad because you cannot see traffic coming in on your left when on the 101 until you're almost on top of them. But this interchange is almost always backed up, so it doesn't seem to matter that much.
https://www.google.com/maps/@37.766537,-122.4053868,118m/data=!3m1!1e3
Another example in California near me, at 1/156, where there's a large amount of space given to allow people to merge.
https://www.google.com/maps/@36.7509069,-121.7678207,99m/data=!3m1!1e3
Another at 101/680 in San Jose, where you can see that they actually striped a brief merging lane. This one has three lanes merging:
https://www.google.com/maps/place/San+Jose,+CA/@37.3434158,-121.8460836,97m/data=!3m1!1e3!4m5!3m4!1s0x808fcae48af93ff5:0xb99d8c0aca9f717b!8m2!3d37.3382082!4d-121.8863286
There are a couple of other examples I can think of in California, but Houston had one for years, at I-45 North/I-610, from NB 45 to EB 610, but they restriped it so that the second lane ends on the ramp.
https://www.google.com/maps/@29.8133052,-95.3729883,85m/data=!3m1!1e3
In many cases, it seems like most drivers who know about this avoid the immediate-merge lane on the ramp.
I'd be curious to hear of other examples and how well they work as far as traffic flow.
Like this? https://goo.gl/maps/WnQ1pAAuRdK2 The AC Expressway (left) meets with Rt. 42 (right). The ACX left lane and Rt. 42 right lane continue thru. The ACX right lane and the Rt. 42 left lane merge into one lane.
While it's not exactly the ramp that you're referring to, it's basically the same thing. In this case, the combined lane gets a good amount of use, and people are generally aware of it enough to zipper it pretty good maintaining a constant speed.
Yes, that's what I was referring to. It looks like some space is given there to mitigate the surprise of seeing someone closing in on you in your lane, and you can see the merge coming for some time on both sides. I would say this is executed quite well.
I would personally rather have the left lane end a bit down the road like a normal merge.
The NJ Turnpike, at the dual-dual merge point south of Interchange 6, has a similar situation where the inner right lane and the outer left lane zipper into each other. That one is much more extended (and well signed) compared to the ACX/42 example above.
There's a similar situation at the north end of I-295 at I-95 (Maine Turnpike) in Gardiner, ME (https://goo.gl/maps/4HbYPqbyW9R2). The left lane of the ramp from 295 north merges immediately with the right lane from 95 north, with the other lane from the ramp ending several hundred feet ahead of this point. Luckily you can see well ahead of the merge point if a car is coming up on you, so I don't mind this one too much.
Another one that I do mind more, is where the northbound ramp from I-495 merges onto I-95 north at its north end near Salisbury (https://goo.gl/maps/vEF8qE9TDRG2). I drive this one every time I go back up to Maine, and I'll always move to the right lane on the 495 ramp to prevent the hassle of this "merge or die" situation.
Quote from: coatimundi on November 16, 2016, 03:10:50 PM
I searched for an existing topic on this but was unable to find any, though I also don't know if I'm using the correct terminology.
The scenario is such:
A ramp with two lanes (or more) merges into a multi-laned roadway. The right lane(s) on the merging ramp gets its own lane while the left does not and must immediately merge.
I deal with this on a daily basis as there are two such instances of this at the 280/85 interchange in Cupertino (north 280 on-ramp to north 85 and 85 on-ramp to north 280. In both cases, traffic in the left lane on the ramp must merge with mainline traffic. The 85 on-ramp to north 280 is particularly bad because the right lane becomes an exit-only lane for the Foothill Expwy exit which is less than a 1/4 mile away.
This happens at the I-81/I-88 interchange.
https://www.google.com/maps/@42.1367953,-75.9029023,304m/data=!3m1!1e3
If you are looking to learn more, I've heard them referred to as "inside" or "tapered inside" merges. Illinois is another state that seems to regularly use them. I can't imagine a scenario where it would be more desirable than a parallel merge that drops on the outside.
Several of these in the Charleston, WV area. They're signed as a "Left Lane Merge" on the ramp that loses a lane.
In one case, where westbound US 60 merges onto I-64/I-77, the right lane becomes an exit-only lane for US 60's immediate departure from the freeway.
Quote from: johndoe on November 16, 2016, 07:28:05 PM
If you are looking to learn more, I've heard them referred to as "inside" or "tapered inside" merges. Illinois is another state that seems to regularly use them. I can't imagine a scenario where it would be more desirable than a parallel merge that drops on the outside.
Not only are these all over Illinois, but Illinois is the only place where I recall seeing
two lanes taper at the same merge.
Examples:
https://goo.gl/maps/uVowQecFhbR2
At least the merge is smooth and gradual. I've driven through this so many times that I'm used to it, and I've never seen a problem here.
https://goo.gl/maps/ph3we4qdLdv
I wouldn't call this a bad merge, either. My problem with this interchange is unrelated to the tapered merge.
Quote from: stridentweasel on November 17, 2016, 12:49:59 AM
Quote from: johndoe on November 16, 2016, 07:28:05 PM
If you are looking to learn more, I've heard them referred to as "inside" or "tapered inside" merges. Illinois is another state that seems to regularly use them. I can't imagine a scenario where it would be more desirable than a parallel merge that drops on the outside.
Not only are these all over Illinois, but Illinois is the only place where I recall seeing two lanes taper at the same merge.
Examples:
https://goo.gl/maps/uVowQecFhbR2
At least the merge is smooth and gradual. I've driven through this so many times that I'm used to it, and I've never seen a problem here.
https://goo.gl/maps/ph3we4qdLdv
I wouldn't call this a bad merge, either. My problem with this interchange is unrelated to the tapered merge.
Or like this one:
https://goo.gl/maps/qp6S93thYow
Been a few years since I've used this route, but the ramp from the Verrazano Bridge to the Belt Parkway (heading towards Coney Island) used to be configured that way and likely still is.
Quote from: Brandon on November 17, 2016, 06:51:56 AM
Quote from: stridentweasel on November 17, 2016, 12:49:59 AM
Quote from: johndoe on November 16, 2016, 07:28:05 PM
If you are looking to learn more, I've heard them referred to as "inside" or "tapered inside" merges. Illinois is another state that seems to regularly use them. I can't imagine a scenario where it would be more desirable than a parallel merge that drops on the outside.
Not only are these all over Illinois, but Illinois is the only place where I recall seeing two lanes taper at the same merge.
Examples:
https://goo.gl/maps/uVowQecFhbR2
At least the merge is smooth and gradual. I've driven through this so many times that I'm used to it, and I've never seen a problem here.
https://goo.gl/maps/ph3we4qdLdv
I wouldn't call this a bad merge, either. My problem with this interchange is unrelated to the tapered merge.
Or like this one:
https://goo.gl/maps/qp6S93thYow
That's just a standard gradual lane drop from the right. Strident's examples show the two center lanes merging.
My vote for worst example is in downtown Detroit where northbound I-75 merges to itself transitioning from the Fisher Freeway to the Chrysler Freeway. The merge point is not at all gradual and visibility is limited due to the Jersey barrier and height difference (spin the Street View image around 180 degrees and you'll see what I mean). This is a terrible setup. The right lane of the northbound Chrysler should be painted out to eliminate the lane merge.
https://goo.gl/maps/stPyh72mvNL2
I think the ramp from Maryland Route 24 south to U.S. Route 1 south (the "Bel Air Bypass") near Bel Air, Maryland is one. I know it starts as a two-lane ramp because living in that area I've obviously been on that ramp many times in my life.
Quote from: epzik8 on November 18, 2016, 09:36:57 AM
I think the ramp from Maryland Route 24 south to U.S. Route 1 south (the "Bel Air Bypass") near Bel Air, Maryland is one. I know it starts as a two-lane ramp because living in that area I've obviously been on that ramp many times in my life.
While it starts as a 2 lane ramp, again, just a standard land drop midway down the ramp.
Ohio loves these, especially in the Cleveland area. There's one at either end of the I-271/I-480 concurrency, 3 at the I-90/I-271 interchange and many more in that area. In Columbus, there's one at I-270/I-670.
US 15 South merging into I-180 East in Williamsport. The left lane from the ramp merges (and there is a Yield sign with a LEFT LANE sign underneath), and the right lane of that ramp becomes an Exit Only lane for I-180 Exit 28. On the US 15 ramp itself, the right lane is signed as the Exit 28 Exit Only ramp even though you're not technically on I-180 yet.
There's a sign that's starting to become more common, that signifies this exact scenario. One example: https://www.google.com/maps/@41.5775979,-87.5699497,3a,52.1y,117.96h,89.46t/data=!3m6!1e1!3m4!1sKwo-oxogWzsqvCFxDaB3IA!2e0!7i13312!8i6656
I saw a couple more in my drive to the South.
Quote from: jeffandnicole on November 17, 2016, 08:09:05 AM
That's just a standard gradual lane drop from the right. Strident's examples show the two center lanes merging.
And I was mentioning a different, yet similar situation. I sure as hell didn't expect the analroadgeek.
We have one of these near Murdoch University in Perth, Australia. They've added a 'tiger tail' between the merging and non-merging lane to make the arrangement more clear and to provide a bit of a safety buffer; the left lane shifts to meet the other lanes further down the road.
(https://i.imgur.com/5ty5JU2.png)
(https://i.imgur.com/c0om4RR.png)
goo.gl/E64dGJcontent_copyCopy short URL
(http://goo.gl/E64dGJcontent_copyCopy%20short%20URL)
Quote from: 1995hoo on November 17, 2016, 07:23:26 AM
Been a few years since I've used this route, but the ramp from the Verrazano Bridge to the Belt Parkway (heading towards Coney Island) used to be configured that way and likely still is.
According to Street View, the location noted above is still like this with the same yellow warning sign:
https://goo.gl/maps/T3YjpnmNpLt
Route 3 interchange with 495 North and South in Chelmsford Ma.
Chelmsford, Massachusetts
https://goo.gl/maps/vZGqbompLmM2
There is no signage or striping to guide drivers so many times you end up with five lanes of traffic in the no man's land this creates. Hopefully an ongoing paving project will rectify this but I haven't been through there lately.
This might be a useful warning sign for this: https://goo.gl/maps/D9ABjmx3VtM2
Quote from: paulthemapguy on November 18, 2016, 04:58:38 PM
There's a sign that's starting to become more common, that signifies this exact scenario. One example: https://www.google.com/maps/@41.5775979,-87.5699497,3a,52.1y,117.96h,89.46t/data=!3m6!1e1!3m4!1sKwo-oxogWzsqvCFxDaB3IA!2e0!7i13312!8i6656
Iowa has their own version of that sign at the western I-35/I-80/I-235 interchange (https://www.google.com/maps/@41.5932276,-93.7818925,3a,75y,248.21h,85.96t/data=!3m6!1e1!3m4!1sbvIVgqQmGMZqHpYhRjrC-Q!2e0!7i13312!8i6656?hl=en). They use this merge design a couple times in Des Moines.
I also recall one or two of these merge designs in Kentucky, and one near the Borman in northern Indiana.
None of the merge signs shown so far are MUTCD compliant, although I recall reading somewhere Ohio had permission from FHWA to experiment with one. Seems Ohio was having an accident problem at at least one of these inside lane/forced merges.
Can any engineer explain why the center lanes merge arrangement would ever be preferable to having the right- or left-most lane drop?
Quote from: mcmc on December 18, 2016, 03:03:35 PM
Can any engineer explain why the center lanes merge arrangement would ever be preferable to having the right- or left-most lane drop?
If the outer lane is the one that terminates first, then there is no point to having two lanes on the ramp, because the outer lane would have to merge into the other lane entering the expressway. That would be functionally the same as having two lanes on an entrance ramp merging into one before reaching the expressway's mainline.
Alternately, think about it this way: when the center lanes merge, as in the situation you mentioned, a vehicle in the right lane of the mainline expressway can get out of the way and scoot one lane to the left. In the opposite case, where the outer lane of cars terminates right away, who has to get out of the way of the cars jumping ship from the ending lane? It's the people in the inner lane of the entrance ramp, who aren't sure of where to go yet because they're just now becoming acquainted with mainline traffic. It would be better if the left lane of the entrance ramp went through a merge situation similar to that of a single lane merging onto the highway, then allowing the outer lane's merge onto the mainline to occur at a later time.
Quote from: paulthemapguy on December 19, 2016, 12:51:52 PM
Quote from: mcmc on December 18, 2016, 03:03:35 PM
Can any engineer explain why the center lanes merge arrangement would ever be preferable to having the right- or left-most lane drop?
If the outer lane is the one that terminates first, then there is no point to having two lanes on the ramp, because the outer lane would have to merge into the other lane entering the expressway. That would be functionally the same as having two lanes on an entrance ramp merging into one before reaching the expressway's mainline.
Alternately, think about it this way: when the center lanes merge, as in the situation you mentioned, a vehicle in the right lane of the mainline expressway can get out of the way and scoot one lane to the left. In the opposite case, where the outer lane of cars terminates right away, who has to get out of the way of the cars jumping ship from the ending lane? It's the people in the inner lane of the entrance ramp, who aren't sure of where to go yet because they're just now becoming acquainted with mainline traffic. It would be better if the left lane of the entrance ramp went through a merge situation similar to that of a single lane merging onto the highway, then allowing the outer lane's merge onto the mainline to occur at a later time.
In 99.999999% of the situations, the situation that you say "people aren't sure of which way to go yet" is the situation that occurs.
It's pretty obvious that if you're merging onto a highway, you merge into the lanes that already exist, not the lane that co-existed on the rmap.
Almost got into a wreck at night in Dallas a few years back at this one: https://goo.gl/maps/9B19p8khU1R2
Regular merge sign, and coming around a sharp curve, and I had never been here before to know to look for somebody in a suicide merge.
This interchange is being torn up so this is not like this right now...
The US 52 to I-26 connector heading onto I-26 east (Exit 208) used to have one of these. You were risking your life if you used the left lane of the connector ramp.
An inside lane merge (assuming traffic circulating on the right, merging leftward) is a rational choice if traffic in the far-right lane on the freeway mainline is reliably less dense than traffic in the far-right lane on the ramp. This is not to say that it doesn't cause problems that don't require mitigation. Tiger tails are one approach that has been extensively tested in Britain and works quite well; I am mildly skeptical of the various warning-sign designs that have been tried in the US. Ultimately, I think locals and frequent visitors acclimatize to inside lane merges as a regionalism, which is what they largely are in the US. I also suspect that the jurisdictions that use inside lane merges are more likely to attempt to socialize drivers to expect them by using absent-nose tapers at simple merges.
Quote from: J N Winkler on December 19, 2016, 09:42:29 PM
An inside lane merge (assuming traffic circulating on the right, merging leftward) is a rational choice if traffic in the far-right lane on the freeway mainline is reliably less dense than traffic in the far-right lane on the ramp. This is not to say that it doesn't cause problems that don't require mitigation. Tiger tails are one approach that has been extensively tested in Britain and works quite well; I am mildly skeptical of the various warning-sign designs that have been tried in the US. Ultimately, I think locals and frequent visitors acclimatize to inside lane merges as a regionalism, which is what they largely are in the US. I also suspect that the jurisdictions that use inside lane merges are more likely to attempt to socialize drivers to expect them by using absent-nose tapers at simple merges.
The real problem with the inside lane merge in the way that it exists in most places in the US is that there isn't enough time (space) to merge easily. The examples are so abrupt that it leads to something that is quite dangerous.
The best way to handle this is to allow more time for the merge. The Australian example upthread was a great example of using tapering to allow for more space.
Another example is the merge of the southbound NJ Turnpike car lanes and truck lanes around Exit 6. The 3-lane car lanes and the 3-lane truck lanes are like separate highways that merge at this point to form a single 3-lane carriageway. The left lane of the truck lanes and the right lane of the car lanes merges to form the middle lane of the merged highway, but it does not happen abruptly. Traffic had about 1,200 feet to make the merge and it happens relatively smoothly.
https://www.google.com/maps/@40.0792016,-74.7494773,3a,75y,240.16h,78.3t/data=!3m6!1e1!3m4!1s10zGOOZcv_24g0lmV9Soag!2e0!7i13312!8i6656!6m1!1e1
Quote from: mrsman on December 20, 2016, 11:18:39 PM
The real problem with the inside lane merge in the way that it exists in most places in the US is that there isn't enough time (space) to merge easily. The examples are so abrupt that it leads to something that is quite dangerous.
The best way to handle this is to allow more time for the merge. The Australian example upthread was a great example of using tapering to allow for more space.
This is absolutely right. An inside lane merge is necessary, because otherwise you negate the utility of the rightmost lane entirely. So the best approach is to ensure that the inside lane merge is carried out as safely as possible, giving a nice long taper so that drivers have the utmost time to assess the situation and make their move. The ramp from NB I-355 to EB I-88 is a nice example: a nice, long approach, leading up to a nice long inside lane merge as you move forward, allowing plenty of time for drivers to assess and react.
https://www.google.com/maps/@41.809586,-88.047163,3a,75y,87.43h,91.13t/data=!3m7!1e1!3m5!1sznjCGERmYU7nUiOlorh_0A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DznjCGERmYU7nUiOlorh_0A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D328.6588%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656
Quote from: paulthemapguy on December 23, 2016, 10:09:16 AM
An inside lane merge is necessary, because otherwise you negate the utility of the rightmost lane entirely.
I think I would disagree with this, from a capacity standpoint. Regardless the taper rate of an inside merge (or ability to "see it coming ") the right of way isn't clear. Which lane is supposed to yield? This lack of clarity probably impacts the capacity more than a lane drop and parallel acceleration lane.
Quote from: johndoe on December 23, 2016, 04:48:14 PM
Quote from: paulthemapguy on December 23, 2016, 10:09:16 AM
An inside lane merge is necessary, because otherwise you negate the utility of the rightmost lane entirely.
I think I would disagree with this, from a capacity standpoint. Regardless the taper rate of an inside merge (or ability to "see it coming ") the right of way isn't clear. Which lane is supposed to yield? This lack of clarity probably impacts the capacity more than a lane drop and parallel acceleration lane.
The vehicles merging onto the freeway from the lane that merges, should either yield or speed up while finding their gap in traffic. Those in the lane that gets its own new lane, can do as they please.
Quote from: johndoe on December 23, 2016, 04:48:14 PM
I think I would disagree with this, from a capacity standpoint. Regardless the taper rate of an inside merge (or ability to "see it coming ") the right of way isn't clear. Which lane is supposed to yield? This lack of clarity probably impacts the capacity more than a lane drop and parallel acceleration lane.
Drivers shouldn't assume they have the right of way at any merge. If one is explicitly told to yield, then, yes, one should yield. But in a merge where neither side has a yield sign, drivers should have enough sense to act courteously and cautiously when they see that two vehicles are trying to occupy the same space ahead (slow down a little if necessary, but don't stop if you can avoid it, and don't play chicken). At any rate, this would rarely be an issue if motorists would adhere to the legal following distance, because there would always be a gap in which to merge. This is one reason why I think following distance should be enforced much more often.
This is I-64 EB as it merges onto I-95 SB.
https://goo.gl/maps/N3rEK9P2usM2
The problem here is not only the onramp's left lane merge itself, but the right onramp lane becomes an exit only lane for the upcoming Boulevard exit, which is less than a 1/2 mile away. This creates a serious weaving issue for both interstates and a major chokepoint for I-64 EB traffic during both rush hours.
Brandon, I'm referring to either the mainline lane vs the ramp lane yielding , not the two ramp lanes.
Quote from: stridentweasel on December 23, 2016, 11:33:26 PM
Drivers shouldn't assume they have the right of way at any merge. If one is explicitly told to yield, then, yes, one should yield. But in a merge where neither side has a yield sign, drivers should have enough sense to act courteously and cautiously when they see that two vehicles are trying to occupy the same space ahead (slow down a little if necessary, but don't stop if you can avoid it, and don't play chicken). At any rate, this would rarely be an issue if motorists would adhere to the legal following distance, because there would always be a gap in which to merge. This is one reason why I think following distance should be enforced much more often.
Perhaps this isn't correct legally, but it seems to me anyone in a lane that's ending IS being told to yield. It's their responsibility to find a gap. Sure it's nice to let someone in, but someone in the mainline lane better not be panic-braking. IMO the inside merge leads to more of these "chicken" moments since drivers on both sides aren't clear on priority. (Like walking toward someone and you both go the same way...both accelerate, both decelerate, etc) I suppose one problem with a legal following distance is that it would hurt capacity.
I'm also curious how these merges are modeled in HCM or, more importantly, microsimulation. Does anyone know if this can be done, or how accurate it is?
Quote from: johndoe on December 24, 2016, 02:40:18 PM
I suppose one problem with a legal following distance is that it would hurt capacity.
I'm pretty sure braking a lot to avoid hitting the car ahead when one is following too closely, hurts capacity. I'm pretty sure drivers not leaving a big enough gap to be overtaken, hurts capacity. I'm pretty sure rear-end collisions resulting from following too closely, hurt capacity.
Quote from: johndoe on December 24, 2016, 02:40:18 PMI'm also curious how these merges are modeled in HCM or, more importantly, microsimulation. Does anyone know if this can be done, or how accurate it is?
It can be done: something something Markov chains. Leclerq has apparently been working on capacity at merges at Georgia Tech for the last five years or so, and this 2011 paper is useful partly for the bibliography and partly for the account of how the Newell-Daganzo model works:
http://trafficlab.ce.gatech.edu/sites/default/files/files/documents/leclercq_isttt.pdf
However, I'm not sure work has been done that addresses the capacity and safety profiles of various merge striping patterns. I suspect safety is partly LOS-dependent.
Quote from: johndoe on December 24, 2016, 02:40:18 PM
it seems to me anyone in a lane that's ending IS being told to yield. It's their responsibility to find a gap. Sure it's nice to let someone in, but someone in the mainline lane better not be panic-braking.
It's not always clear at a merge which lane is ending and which lane is continuing. Sometimes the design is more of a "form one lane" type thing. Whenever I encounter situations like this, I assume traffic should simply take turns, and I accelerate or decelerate appropriately.
In the Richmond example posted by
plain above (https://goo.gl/maps/N3rEK9P2usM2 (https://goo.gl/maps/N3rEK9P2usM2)), it's not obvious–or even reasonable to say–whether I-64's lane or I-95's lane is ending.
Quote from: stridentweasel on December 24, 2016, 05:52:42 PM
Quote from: johndoe on December 24, 2016, 02:40:18 PM
I suppose one problem with a legal following distance is that it would hurt capacity.
I'm pretty sure braking a lot to avoid hitting the car ahead when one is following too closely, hurts capacity. I'm pretty sure drivers not leaving a big enough gap to be overtaken, hurts capacity. I'm pretty sure rear-end collisions resulting from following too closely, hurt capacity.
Like the braking that would be required to maintain some arbitrary distance? People can judge for themselves an appropriate gap and densities will adjust accordingly around merge areas.
Thanks JN.
Kphoger: to me this lack of clarity is exactly why I cannot imagine a scenario where the inside merge is a good option. I can't imagine how a parallel acceleration lane followed by a taper wouldn't always be more clear.
Quote from: johndoe on December 25, 2016, 12:22:51 AM
Quote from: stridentweasel on December 24, 2016, 05:52:42 PM
Quote from: johndoe on December 24, 2016, 02:40:18 PM
I suppose one problem with a legal following distance is that it would hurt capacity.
I'm pretty sure braking a lot to avoid hitting the car ahead when one is following too closely, hurts capacity. I'm pretty sure drivers not leaving a big enough gap to be overtaken, hurts capacity. I'm pretty sure rear-end collisions resulting from following too closely, hurt capacity.
Like the braking that would be required to maintain some arbitrary distance?
No, because people have to slow down more suddenly when they're following too closely. When maintaining the correct following distance, one can slow down gradually to maintain the gap when the car ahead slows down gradually. When following too closely, the car doing the following has to slow down more quickly than the car ahead. This is why, if you follow someone too closely, it increases
your chances of being rear-ended. You can probably brake fast enough to avoid hitting the car in front of you, but when you have to brake very suddenly just to avoid hitting the car in front of you, because you were following too closely, and
someone else is following
you too closely, guess what's likely to happen?
Quote
People can judge for themselves an appropriate gap and densities will adjust accordingly around merge areas.
Except they too often don't. Too often, people just follow about as closely as they can without hitting the car ahead of them. Two seconds is a good rule of thumb (for passenger cars on dry pavement), but how often do you really see people leave that much space? People too often don't even leave
one second of following distance. At any rate, people are
supposed to leave enough of a gap to be overtaken, but how often do you really see them make an earnest effort to do
that? If one is just leaving enough space to avoid hitting the car ahead, that's not enough of a gap to be overtaken. And if a driver isn't leaving enough of a gap to be overtaken, it hurts merge situations, because it reduces the availability of gaps in which people can safely merge.
Strident,
I don't really want to hijack this thread (especially since inside merges are such an interesting feature), so here are my last thoughts on this:
You're right that some people accelerate and decelerate too much to make me comfortable. I'm more of a bigger-headway guy myself. But I don't see how changing (or cracking down on?) the law would improve situations. For one, I'm not sure how headways could be enforced by police. And even if they could, you mentioned how a constant value doesn't exist. (Is it raining? Are my brakes poor? Am I in the middle of nowhere? Is there a ramp ahead with 10 cars merging?) Plus, I'm pretty sure we don't need to give police any more reason to pull over drivers in peak periods :-D
VISSIM, the microsimulation program used by many DOT, uses a car-following model called Wiedemann 99. The default value for headway (CC1) is 0.9 seconds. Here's a snippet from the WSDOT VISSIM protocol (http://www.wsdot.wa.gov/NR/rdonlyres/378BEAC9-FE26-4EDA-AA1F-B3A55F9C532F/0/VissimProtocol.pdf) (https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2F2qu87y9.png&hash=d937a270991dffb40ff002d5682b0da7e4a1a7b3)
A CC1 of 2 seconds isn't even on the chart because it's so unrealistic, but I think you can "guess what's likely to happen?" to flow rates (and upstream congestion).
Another cool site related to that car-following model is http://w99demo.com/ You can see the action of all the vehicles (accel, follow, decel) and play with differing parameters.
Quote from: johndoe on December 26, 2016, 10:19:12 AM
For one, I'm not sure how headways could be enforced by police.
I was under the impression that the highway patrol cars in Germany were equipped with cameras and the technology needed to measure following distance, and that they are therefore able to issue valid citations for too-close following distance.
Quote from: johndoe on December 26, 2016, 10:19:12 AM
Strident,
I don't really want to hijack this thread (especially since inside merges are such an interesting feature), so here are my last thoughts on this:
You're right that some people accelerate and decelerate too much to make me comfortable. I'm more of a bigger-headway guy myself. But I don't see how changing (or cracking down on?) the law would improve situations. For one, I'm not sure how headways could be enforced by police. And even if they could, you mentioned how a constant value doesn't exist. (Is it raining? Are my brakes poor? Am I in the middle of nowhere? Is there a ramp ahead with 10 cars merging?) Plus, I'm pretty sure we don't need to give police any more reason to pull over drivers in peak periods :-D
VISSIM, the microsimulation program used by many DOT, uses a car-following model called Wiedemann 99. The default value for headway (CC1) is 0.9 seconds. Here's a snippet from the WSDOT VISSIM protocol (http://www.wsdot.wa.gov/NR/rdonlyres/378BEAC9-FE26-4EDA-AA1F-B3A55F9C532F/0/VissimProtocol.pdf)
(Image snipped to save space.)
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A CC1 of 2 seconds isn't even on the chart because it's so unrealistic, but I think you can "guess what's likely to happen?" to flow rates (and upstream congestion).
Another cool site related to that car-following model is http://w99demo.com/ You can see the action of all the vehicles (accel, follow, decel) and play with differing parameters.
This article, posted in an earlier thread, is rather informative and relevant: http://www.wsj.com/articles/one-driver-can-prevent-a-traffic-jam-1476204858
Quote from: johndoe on December 26, 2016, 10:19:12 AM
For one, I'm not sure how headways could be enforced by police. And even if they could, you mentioned how a constant value doesn't exist. (Is it raining? Are my brakes poor? Am I in the middle of nowhere? Is there a ramp ahead with 10 cars merging?) Plus, I'm pretty sure we don't need to give police any more reason to pull over drivers in peak periods :-D
Around here they do occasionally pull people over for their following distance and being obnoxious letting people in. One of my buddys actually got a ticket for it. Its done totally by eye, arbitrarily. Personally, I'd rather the cops pull people over during peak periods when a couple of assholes are ruining it for the rest of us vs non-peak periods where someone being an asshole is easily avoided by giving them their space.
Quote from: Brandon on December 23, 2016, 05:40:25 PM
The vehicles merging onto the freeway from the lane that merges, should either yield or speed up while finding their gap in traffic. Those in the lane that gets its own new lane, can do as they please.
Sounds good in theory, does not work well in practice with either large trucks or those drivers who refuse to accelerate until already completely merged onto the freeway. The latter case usually gets exacerbated by other drivers cutting across the painted gore and instead of waiting for the merge.
Quote from: paulthemapguy on December 23, 2016, 10:09:16 AM
The ramp from NB I-355 to EB I-88 is a nice example: a nice, long approach, leading up to a nice long inside lane merge as you move forward, allowing plenty of time for drivers to assess and react.
https://www.google.com/maps/@41.809586,-88.047163,3a,75y,87.43h,91.13t/data=!3m7!1e1!3m5!1sznjCGERmYU7nUiOlorh_0A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DznjCGERmYU7nUiOlorh_0A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D328.6588%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656
That one does not work very well IMHO; there's usually too much traffic on EB I-88 trying to position for the ramp to NB I-355. Additionally, given the length of the painted merge gore, there is only about ~250 feet (around 2.5 seconds at what is supposed to be the speed limit on the tollway) for the inside ramp lane and outside lane of I-88 for two vehicles to decide who will actually give way.
Quote from: Revive 755 on December 28, 2016, 09:49:38 PM
Quote from: paulthemapguy on December 23, 2016, 10:09:16 AM
The ramp from NB I-355 to EB I-88 is a nice example: a nice, long approach, leading up to a nice long inside lane merge as you move forward, allowing plenty of time for drivers to assess and react.
https://www.google.com/maps/@41.809586,-88.047163,3a,75y,87.43h,91.13t/data=!3m7!1e1!3m5!1sznjCGERmYU7nUiOlorh_0A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DznjCGERmYU7nUiOlorh_0A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D328.6588%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656
That one does not work very well IMHO; there's usually too much traffic on EB I-88 trying to position for the ramp to NB I-355. Additionally, given the length of the painted merge gore, there is only about ~250 feet (around 2.5 seconds at what is supposed to be the speed limit on the tollway) for the inside ramp lane and outside lane of I-88 for two vehicles to decide who will actually give way.
Well, it's better than some of the single-lane entrance ramp convergences that are out there. I like that there's a considerable amount of side-by-side travel before the point of convergence. That is more important for anticipating traffic than the gore zone itself. (imo of course)
https://goo.gl/maps/UAE6NU8F2Vv
...But I find it utterly unacceptable that this sign doesn't have a yellow "EXIT V ONLY" arrow
https://goo.gl/maps/xAsVwWXU3z32
Quote from: cl94 on November 18, 2016, 10:12:11 AM
Ohio loves these, especially in the Cleveland area. There's one at either end of the I-271/I-480 concurrency, 3 at the I-90/I-271 interchange and many more in that area. In Columbus, there's one at I-270/I-670.
Also in Cincinnati where 74 merges into 75 South.