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"Congestion-Proof" Freeways

Started by webny99, December 13, 2022, 10:26:44 AM

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Bobby5280

Exit ramps are going to vary in their likelihood of causing back-ups into freeway main lanes. Much of it depends on the location, the design/length of the ramp and then whatever snarl of traffic signals exists at the end of the ramp on the surface street level.

In the past couple or so decades I've noticed Texas (and some other states) changing the locations of exit slip ramps to frontage roads. Traditionally you would see a slip ramp from the freeway to frontage road shortly before a significant intersection. Now they're often reversing this arrangement, placing exit ramps after the intersection and on-ramps before it. Exiting traffic must drive farther to reach the desired intersection. But that added distance provides room for more vehicles to disperse into side streets, driveways, etc before the next at-grade signal light. With the old arrangement exiting traffic could more easily clog the exit ramp.


webny99

Quote from: webny99 on November 04, 2024, 12:11:45 PM
QuotePlenty of freeway to freeway interchange ramps are inadequate. They'll have a single lane when they need to be two or even three lanes wide.

This is also true, but the question is how much congestion is caused by ramp constraints vs. mainline constraints. I find that a fascinating and seemingly very under-studied/under-discussed question, so I'm going to do a bit of a deep dive for my area (upstate NY) - be interesting to see how it tracks with other areas.

Using my own experience and historical maps data saved on my phone to identify the most common AM and PM congestion hot spots, I bucketed them into being caused by a mainline constraint, a ramp constraint, or a mix of both. I tried to be pretty comprehensive here, so there's probably room for nuance on some of them, but in most cases the constraint was pretty clear.

AM
1. I-590 SB Exits 5-6: mainline constraint (backs up from I-490 WB merge)
2. NY 590 SB Exits 7-11: mainline constraint (backs up from Exit 7 merge)
3. I-490 WB Exits 21-23: mix of both (backs up from the Exit 23 merge, exacerbated by Exit 22 weave and heavy traffic shifting right to take Exit 21)
4. I-490 EB Exits 8-9: mix of both (backs up from the Exit 8 merge, exacerbated by through and I-390 SB traffic shifting right)
5. I-490 EB Exits 10-13: mainline constraint (general slowness due to heavy entering traffic)
6. I-390 SB Exits 19-20: mainline constraint (post-Exit 20 reconstruction, backs up from lane drop at Exit 19)
7. I-390 SB Exits 17-18: mainline constraint (backs up from Exits 17 and 18 merges)

PM
1. I-590 NB Exits 1-4: mainline constraint (backs up from Exits 2 and 3 merges)
2. NY 590 NB Exits 5-6: mainline constraint (backs up from Exit 5 merges)
3. NY 590 NB Exits 8-10: ramp constraint (backs up from Exit 10B)
4. I-490 EB Exits 19-21: mix of both (backs up from the Exit 19 merge, exacerbated by heavy traffic shifting right to take Exits 20 and 21)
5. I-490 WB Exits 21-24: ramp constraint (backs up from Exit 21 ramp to NY 590 NB, affecting the Exit 23 merge)
6. I-490 WB Exits 9-13: mainline constraint (backs up from Exit 13 merge; general slowness due to heavy entering traffic)
7. I-390 NB Exits 16-20: mainline constraint (general slowness due to heavy entering traffic)
8. I-490 EB at I-90 EB (Seasonal: summer/fall only): ramp constraint (backs up from single lane ramp to I-90 EB)

So out of 15 identified congestion hot spots, 9 are primarily due to mainline constraints, 3 are primarily due to ramp constraints, and 3 are a mix of both.

achilles765

Quote from: Bobby5280 on November 04, 2024, 03:39:27 PMExit ramps are going to vary in their likelihood of causing back-ups into freeway main lanes. Much of it depends on the location, the design/length of the ramp and then whatever snarl of traffic signals exists at the end of the ramp on the surface street level.

In the past couple or so decades I've noticed Texas (and some other states) changing the locations of exit slip ramps to frontage roads. Traditionally you would see a slip ramp from the freeway to frontage road shortly before a significant intersection. Now they're often reversing this arrangement, placing exit ramps after the intersection and on-ramps before it. Exiting traffic must drive farther to reach the desired intersection. But that added distance provides room for more vehicles to disperse into side streets, driveways, etc before the next at-grade signal light. With the old arrangement exiting traffic could more easily clog the exit ramp.

One of the most sure fire ways to determine how old a stretch of freeway is in Texas is to check how far from the Desired intersection the off ramp is. Except for areas with a lot of exits super close together, or where there are no frontage roads, backups from exiting traffic are rare. One notable exception I can think of is IH 45 in north Houston because many of the ramps are right before the intersection and there is so much traffic cramped into the four lanes.
I love freeways and roads in any state but Texas will always be first in my heart

mrsman

Not sure if this is meant for the spirit of this thread, but here are some of the freeways that I've experienced as congestion proof.  In many cases, the lane configuration leads to this result, where the freeway just widens or a surface street enters a freeway and the simple existence of the widening and/or closed access provides the desired result, at least for a short bit.

I-105 EB near LAX doesn't ever really have any congestion until after I-405.
CA-90 Marina Freeway is so short that it doesn't carry regional traffic and does widen to 4 lanes in each direction at one point.
CA-170 SB has more lanes than what I-5 feeds into it and doesn't back up until Burbank Blvd (backups due to the upcoming 101/170/134 interchange)
I-710 stubways are low traffic (SB south of Valley Blvd, NB north of California Ave in the Alhambra/Pasadena area)
CA-2 was already mentioned.
I-210 between Pasadena and San Fernando is likely a similar phenomenon, since very few of the area freeways reach it. 

In many cases, the extra lane comes in from a surface street, but there isn't nearly as much traffic from the surface street, so there is no backup.

I notice this on a brief section of I-678 NB in Queens, NY when traffic coming from the Jackie Robinson Parkway joins 2 lanes of I-678.  The two lanes are congested, but the third lane does provide relief until you reach I-495.

There is also a brief section of NB I-270 spur in Bethesda, MD that also moves well due to the many lanes, until the spur merges in with the regular I-270.



pderocco

Quote from: mrsman on November 18, 2024, 04:03:28 PMNot sure if this is meant for the spirit of this thread, but here are some of the freeways that I've experienced as congestion proof.  In many cases, the lane configuration leads to this result, where the freeway just widens or a surface street enters a freeway and the simple existence of the widening and/or closed access provides the desired result, at least for a short bit.

I-105 EB near LAX doesn't ever really have any congestion until after I-405.
That's why it shows up in car commercials now and then. It's one of the few freeways they're willing to shut down for a bit for some filming.

Henry

Quote from: pderocco on November 19, 2024, 01:59:34 AM
Quote from: mrsman on November 18, 2024, 04:03:28 PMNot sure if this is meant for the spirit of this thread, but here are some of the freeways that I've experienced as congestion proof.  In many cases, the lane configuration leads to this result, where the freeway just widens or a surface street enters a freeway and the simple existence of the widening and/or closed access provides the desired result, at least for a short bit.

I-105 EB near LAX doesn't ever really have any congestion until after I-405.
That's why it shows up in car commercials now and then. It's one of the few freeways they're willing to shut down for a bit for some filming.
The original Speed movie is celebrating its 30th anniversary this year, and IIRC, it was the first ever to be filmed on that freeway, prior to opening to traffic.
Go Cubs Go! Go Cubs Go! Hey Chicago, what do you say? The Cubs are gonna win today!

dantheman

US 44 EB in Massachusetts, from just west of MA 58 to the MA 3 interchange, almost fits the bill. It is a super-2 west of here, and expands to four lanes just before MA 58. Technically, enough traffic could enter at MA 58 or the subsequent to outweigh the added lane and cause congestion - but I've never seen much traffic at all enter on those ramps, and certainly not enough to double the amount of traffic on US 44.

This stretch of highway is also a rare instance of an "island" of a 65 mph speed limit: US 44 west of the four-lane piece is 55 mph and MA 3 is 60 mph, so the 65 mph stretch of US 44 does not connect to any other 65 mph highways.

While it is a very short stretch, the expansion of CT 9 SB from two lanes to five in New Britain, just before CT 72, probably also qualifies!

architect77

Georgia's Express Lanes have only 1 purpose: Give drivers the option to pay to use free-flowing lanes at a minimum 45mph or faster, 24/7.

The variable toll rate rises to discourage too many from entering the lanes to keep the flow at 45mph or greater.

These are the epitome of congestion-proof lanes. Only voluntary users pay for the lanes' construction and maintenance, and no other citizens can complain about their tax dollars being used, road-haters can't scream induced demand,etc.

All citizens of all income levels can use the lanes whenever they must get somewhere faster, sometimes afternoon I-85 prices rise to $20 per trip, but apparently that extra hour with their families is sometimes worth that much.

I think it's a great offering to combat gridlock in a large metro area. The new lanes being built are separated or elevated so that they don't succumb to slow downs/accidents in the general purpose lanes. Only I-85's one HOT lane is part of the free lanes.

This is smart increasing of capacity for a growing metro. Capacity much grow commensurate with the population or quality of life is decreased for everyone.

roadman65

Delaware keeping DE 1 as limited access around Smyrna and Dover is that keeping local traffic off the freeway is keeping DE 1 free flowing for through motorists.
Every day is a winding road, you just got to get used to it.

Sheryl Crowe



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