Ramp Metering - Pros and Cons

[Indyroads]

I have seen many metro areas LA, SAC, SF, ATL, SEA, etc. use ramp metering signals to help mitigate traffic congestion at freeway entrance ramps, My question is are they succesful ultimately in reducing or eliminating some traffic jams? Thoughts?

[NE2]

The problem that they solve is that traffic on an onramp often comes in pulses due to a traffic light. A ramp meter spreads it out.

[froggie]

Depending on ramp volume and how restrictive the ramp meter is, ramp traffic can back up onto the cross road, but there have been well-documented improvements in capacity, peak hour speeds, and crash rate on freeways with implementation of ramp metering.  Typically with an urban freeway, at-speed "capacity" is about 2000 vehicles per lane per hour (vplph)..."at-speed" being where you can reasonably go at or close to the speed limit.  In congested conditions, you can get about 2200 vplph.  MnDOT has documented cases of squeezing 2400+ vplph on freeways with ramp metering.

The main downside is the potential for ramp spillover onto the side road.

[Big John]

I have seen loop detectors at the start of the metered ramp and if it detects traffic stopped on it, meaning it is backed up all the way, the ramp meter is supposed to either increase the pace of letting vehicles through or momentarily let all vehicles through before resetting.

[colinstu]

Has anyone seen a stop sign used at a single lane entrance ramp? Maybe with a small sign posted below it telling it's only effective at certain times (rush hours)?

Seems like an easy cost-cutting measure to a new ramp (or retrofitting an old ramp) instead of running power lines and new signals.

edit: wouldn't always be the most effective. Some traffic meters are set at such a quick pace it feels like a stop sign. Some feel like double that time.

[myosh_tino]

I have seen loop detectors at the start of the metered ramp and if it detects traffic stopped on it, meaning it is backed up all the way, the ramp meter is supposed to either increase the pace of letting vehicles through or momentarily let all vehicles through before resetting.

Caltrans places loop detectors on the freeway to tell the metering light (that's what we call them out here) how fast to cycle.  IIRC, Caltrans sets the minimum cycle time for the metering light (1 car every 8 seconds for example) but if the detector loops sense that freeway traffic is slowing, it can instruct the metering light to slow down (say from 1 car every 8 seconds to 1 every 12 seconds) in an  attempt to keep freeway traffic moving.

Caltrans also places detector loops on the ramp itself but only near the limit line so the meter knows a car is approaching and/or waiting.

[Alex]

Depends on the perspective. When I was already on the 5 they were useful, but when I was getting on the 5, they sometimes were a thorn in my side. The HOV aspect doesn't help much either if you can't get to where that lane begins. Here's a typical Caltrans configuration with the HOV-2 lane in use:



Still, I like the fact that they offer breaks to the constant flow of merging traffic onto the freeway mainline.

[The High Plains Traveler]

MnDOT aggressively implemented metering in the 1990s in the Twin Cities, including on freeway-freeway ramps. At some locations, they had intervals between cars of up to 30 seconds. I have sat as long as 20 minutes queued up waiting to enter the freeway, and that did cause backup onto the surface street. They relaxed that considerably, though I haven't driven rush hour Twin Cities freeways for a long time to judge how they work now. I do experience them in Denver, which never has more than 10 seconds between green lights, and typically allows two cars to pass the lights at once.

[Brandon]

I'm not really a fan of ramp metering.  All it seems to do, at least around Chicago, is to slow the speed at which one enters the expressway.  There seems to be no difference in finding a spot on the expressway as the typical Chicago driver closes up and refuses to zipper.  I'd say about one third of those entering the expressways around here ignore the meters and just go anyway.

[Thing 342]

The ones I used in Phoenix were decent, even though they were basically stop signs.

However, the ones I've used in Atlanta were awful. It one took me ~10 minutes just to get on 285 from Peachtree Industrial Blvd.

I think ramp meters are good when done right.

[agentsteel53]

I don't mind them unless they are freeway-to-freeway.  especially the one at CA-2 NB approaching I-210.  I've seen them active when there was almost no traffic, necessitating a seemingly random stop-and-go.

[roadman65]

We could use them in Orlando on I-4, but good luck in getting our resident commuters to pay attention to them!  I believe that is why FDOT does not want them for that reason.

[Brandon]

We could use them in Orlando on I-4, but good luck in getting our resident commuters to pay attention to them!  I believe that is why FDOT does not want them for that reason.

Never stopped IDOT and the City of Chicago (see my comment above).

[Alex]

I don't mind them unless they are freeway-to-freeway.  especially the one at CA-2 NB approaching I-210.  I've seen them active when there was almost no traffic, necessitating a seemingly random stop-and-go.

Ramp meters should never be used at freeway to freeway connections. I always thought those ones in Los Angeles were ridiculous.

[roadman65]

You mean there are some freeway to freeway that actually have them.  That is almost like a Breezewood!

[Alps]

I don't mind them unless they are freeway-to-freeway.  especially the one at CA-2 NB approaching I-210.  I've seen them active when there was almost no traffic, necessitating a seemingly random stop-and-go.

Ramp meters should never be used at freeway to freeway connections. I always thought those ones in Los Angeles were ridiculous.

San Diego, too. http://goo.gl/maps/X9wYF

[agentsteel53]

San Diego, too. http://goo.gl/maps/X9wYF

that one (about 3 miles south of my house!), I can almost see the virtues of.  the 67 SB to 8 WB transition is a merge of 1, 2, and 1 lanes down to 1.  the 2 is the southbound lanes of 67, carrying the majority of traffic, which is expanded to three lanes of ramp metering.  the two 1s are surface street ramps, due to the fact that current 8/67 was effectively built on top of 8/old 67.

it's a pretty wonky intersection for sure.  there are still some original 1961 signs from the first 67/8 junction around... interestingly, they are button copy, not porcelain.

a somewhat worse example is 125 southbound at 8.  not only are there metering lights for a non-transition (!), but 125 merges down to a single lane just south of I-8 while there is perfectly well-paved concrete available to keep it at least two lanes wide!.  between this, some quirky interchanges with surface streets, the utterly stupid junction with 94 (complete with self-exit), another self-exit at 54, the fact that the southernmost several miles are a toll road that failed to pay for itself, and the clusterfuck that is the 125/905 non-junction... yep, 125 is the bastard child of the San Diego freeway network.

[Ned Weasel]

Has anyone seen a stop sign used at a single lane entrance ramp?

I have, but not in the way you're thinking!

(At least I'm pretty sure you're not thinking of the way Pennsylvania uses them for extremely short or non-existent acceleration lanes.)

Maybe with a small sign posted below it telling it's only effective at certain times (rush hours)?

Seems like an easy cost-cutting measure to a new ramp (or retrofitting an old ramp) instead of running power lines and new signals.

edit: wouldn't always be the most effective. Some traffic meters are set at such a quick pace it feels like a stop sign. Some feel like double that time.

That might be harder to enforce than a traffic signal, unless sensors can reliably detect a full stop versus a rolling "stop" or a blatant non-stop.

[vdeane]

Wouldn't meters cause massive problems by causing traffic to merge into the freeway from a stop rather than at speed?  Everything I know about merging says you use the ramp to accelerate so that you're going freeway speed by the time you get to the acceleration lane.

[NE2]

Wouldn't meters cause massive problems by causing traffic to merge into the freeway from a stop rather than at speed?  Everything I know about merging says you use the ramp to accelerate so that you're going freeway speed by the time you get to the acceleration lane.

They're ideally far enough back that you can accelerate normally.

[MASTERNC]

You also need enough of an acceleration lane to safely merge.  I think that's the reason why PennDOT disabled one of the ramp meters on I-476 (NB from US 30) because the acceleration lane is short past the meter (there is a railroad overpass shortly after the ramp).  The acceleration lane going southbound is much longer and the meter is still in use there.

I also think that is why ramp meters have never been installed on I-76, although IMHO they might help reduce some congestion, especially eastbound between I-476 and US 1.

[myosh_tino]

Ramp meters should never be used at freeway to freeway connections. I always thought those ones in Los Angeles were ridiculous.

San Diego, too. http://goo.gl/maps/X9wYF

We've got freeway-to-freeway metering lights on Bay Area freeways too...

* US 101/CA-85 --- South San Jose, NB 101 to NB 85 is active
* US 101/I-280/I-680 --- SB 280 & NB 680 to NB 101 is active
* CA-85/CA-17 --- NB/SB 17 to NB 85 active in morning, to SB 85 active in evening
* CA-87/CA-85 --- SB 85 to NB 87 active in morning, SB 87 to SB 85 active in evening
* CA-87/I-280 --- NB/SB 87 to NB/SB 280 active
* CA-87/US 101 --- NB 87 to NB 101 active
* CA-237/US 101 --- EB 237 to SB 101 active
* CA-237/I-880 --- EB 237 to NB 880 active
* CA-92/I-880 --- EB 92 to NB 880 active

In addition to the above list (which isn't complete by any means), freeway-to-freeway metering lights are being installed on the ramp from NB 280 to NB & SB 85 and from EB 237 to NB 85.  These lights are part of a project to install metering lights on all ramps on the 1970's segment of CA-85 from I-280 in Cupertino to US 101 in Mountain View.

[jeffandnicole]

New Jersey had ONE ramp with ramp meters. GSV only has a view from the main highway, not the ramp itself:  http://goo.gl/maps/tVQHE

This is located in Atlantic City's Marina section, where traffic leaving Harrahs Casino exits onto NJ 87 South (West) towards the AC Expressway Tunnel.  87 isn't what most people consider a highway (although it is limited access for its mile or so length)...35 mph speed limit and very light traffic coming from Brigantine. The meters were in use 24/7, although they appeared to blink randomly between Red & Green to meter the occasional car onto lightly used 87, regardless if traffic was present or not on either the ramp or highway.

The meters may have been in use for 2 years, max, before the ramps was redesigned, moving the ramps slightly to the right.  The meters were never removed though, and with the link above, you can still see them in the island between the on and off ramps, unutilized.

[ET21]

I'm not really a fan of ramp metering.  All it seems to do, at least around Chicago, is to slow the speed at which one enters the expressway.  There seems to be no difference in finding a spot on the expressway as the typical Chicago driver closes up and refuses to zipper.  I'd say about one third of those entering the expressways around here ignore the meters and just go anyway.

If they can even make it to the actual ramp meter. There have been occasions, especially on the side streets next to the Kennedy, that would be backed up for blocks because of how backed up the Kennedy was. At that point, ramp metering goes out the door and it's every man for himself

[Fleetwood Mac Attack]

Hey all,

Curious to know if anyone is aware of any instances of a new ramp metering install actually increasing crashes at first due to a lack of driver awareness? Seems like this could be an issue if drivers are clueless enough. Basically, are there any documented instances of increased safety on a freeway mainline being "traded off" with reduced safety on ramps/side streets?