Should Cities Help Drivers Hit Green Lights All the Time?

[tradephoric]

It's not a technical term, but to me a "soft stop"  is when a driver has to come to a complete (or near complete) stop for only a few moments at a red light.  When a corridor is timed for exactly the posted speed limit, the platoon of vehicles coming from an upstream signal can experience these "soft stops"  since a percentage of drivers are always going to drive above the posted speed limit and get to the light early.

[mrsman]

Don't think they need "smart" signals, just well-timed signals.  A well-timed set of signals can also help regulate the speeds along the street.

You know, it's funny....if I'm driving on either of the paired one-way streets that carry US-1 through Old Town Alexandria, Virginia, I can hit all the green lights on that section* in succession–if I exceed the 25-mph speed limit by at least 5 mph (which is not always possible due to traffic, of course). If I go the speed limit, I invariably have to stop for multiple lights. That tells me either the lights are mistimed or the speed limit is set incorrectly.

The "green wave" you can encounter in New York is all too rare elsewhere.

I have noticed this  as well - it seems to be more obvious when driving southbound on the Henry Street part of the couplet than it is northbound.  Not sure why.

I do know that severe afternoon peak-period traffic congestion on Henry Street (including gridlocking to the point that the city had to assign traffic control officers at each intersection) went away when the Woodrow Wilson Bridge reconstruction project was complete enough to have both spans between Alexandria and Prince George's County open to traffic.

This sounds like a situation where they lowered the speed limit but never changed the light timing on the signals.

[1995hoo]

Don't think they need "smart" signals, just well-timed signals.  A well-timed set of signals can also help regulate the speeds along the street.

You know, it's funny....if I'm driving on either of the paired one-way streets that carry US-1 through Old Town Alexandria, Virginia, I can hit all the green lights on that section* in succession–if I exceed the 25-mph speed limit by at least 5 mph (which is not always possible due to traffic, of course). If I go the speed limit, I invariably have to stop for multiple lights. That tells me either the lights are mistimed or the speed limit is set incorrectly.

The "green wave" you can encounter in New York is all too rare elsewhere.

I have noticed this  as well - it seems to be more obvious when driving southbound on the Henry Street part of the couplet than it is northbound.  Not sure why.

I do know that severe afternoon peak-period traffic congestion on Henry Street (including gridlocking to the point that the city had to assign traffic control officers at each intersection) went away when the Woodrow Wilson Bridge reconstruction project was complete enough to have both spans between Alexandria and Prince George's County open to traffic.

This sounds like a situation where they lowered the speed limit but never changed the light timing on the signals.

Later this year I will have lived in this area for 40 years, and in that time I don't ever remember the speed limit on that road being higher than 25 mph.

[DeaconG]

Back in the early to mid 70's Philadelphia used to have a system like that on Chestnut and Walnut Streets (PA 3), every two to three blocks you would see a sign mounted on a pole beside the traffic light with a variable speed limit sign, usually set at 35; if you went at that speed when the light changed green you could travel quite a few city blocks before you got stopped at a light (IIRC, usually you got stopped at 60th, 52nd and 44th Streets whether you liked it or not).

I thought it was a quite neat and smart way to keep the traffic moving; alas, that experiment only lasted a couple of years before those signs got removed and the timing was changed back.

[JoePCool14]

Illinois tries to make drivers hit red lights. Its pretty sad.

[agentsteel53]

what we need is more permissive turns, as opposed to outright forbidden ones.  California has nearly all of its intersections with turn phases set to forbidden during the non-turn phases, even though there is damn near nobody coming and one could safely squeeze several turning cars through the intersection with a permissive green.

hell, I'd even advocate that red lights should be treated as stop signs.  you may go, but yield to everyone.  basically, allow right turn on red to be expanded to straight and left on red after stop. 

traffic lights where you're stopped for absolutely no one are the worst.

[tradephoric]

Re-timing a corridor with bad geometry is like putting new tires on a car without an engine... it doesn't fix much.  A city needs a good grid layout if they want to keep traffic moving. 

[Scott5114]

what we need is more permissive turns, as opposed to outright forbidden ones.  California has nearly all of its intersections with turn phases set to forbidden during the non-turn phases, even though there is damn near nobody coming and one could safely squeeze several turning cars through the intersection with a permissive green.

hell, I'd even advocate that red lights should be treated as stop signs.  you may go, but yield to everyone.  basically, allow right turn on red to be expanded to straight and left on red after stop. 

traffic lights where you're stopped for absolutely no one are the worst.

This is said a lot, but I think it's worse to have a permissive turn when you really need a protected, such that the left turn lane backs up, since only one or two cars can get through breaks in oncoming traffic on each cycle. There's a few of these in Norman, and I would much rather have a longer nominal wait with a guaranteed chance of going when the light turns green rather than a "here, the light is theoretically green. good luck!" permissive.

[vdeane]

That's why I like doghouse signals.  The left turning traffic has a guaranteed time to go when the arrow is on, and can go at other times when traffic allows.  You get the positives of both and the negatives of neither.

[tradephoric]

^Other than safety considerations.  A permissive-protected left-turn is going to have a higher crash rate than a protected only left-turn.

[vdeane]

I don't think we should set traffic policy based on the lowest common denominator.

[tradephoric]

The negative side of a permissive-protected left turn is that they have higher crash rates than protected-only left turns.  You said "That's why I like doghouse signals.   You get the positives of both and the negatives of neither."

I like doghouses too, but there are negatives (ie. higher crash rates).

[vdeane]

The crash rates are caused mostly by bad driving.  As I said, I don't think we should set traffic policy to the lowest common denominator.

The rest of the crash rates are mostly bad engineering.  Don't give one side an extended green.  Don't make it illegal to be in an intersection with a red signal if you entered on a green or yellow.  Stuff like that.  I've never had a problem making a left turn at a doghouse signal.  I almost always get infuriated at a protected-only turn.

[Alps]

The crash rates are caused mostly by bad driving.  As I said, I don't think we should set traffic policy to the lowest common denominator.

The rest of the crash rates are mostly bad engineering.  Don't give one side an extended green.  Don't make it illegal to be in an intersection with a red signal if you entered on a green or yellow.  Stuff like that.  I've never had a problem making a left turn at a doghouse signal.  I almost always get infuriated at a protected-only turn.

Um... It's simple fact that permitted left turns lead to more crashes than protected-only left turns. You have no conflicting traffic when it's protected, but you do have conflicts when it's permitted. Conflicts = crashes.

[agentsteel53]

Um... It's simple fact that permitted left turns lead to more crashes than protected-only left turns. You have no conflicting traffic when it's protected, but you do have conflicts when it's permitted. Conflicts = crashes.

you are literally correct.  however, come out to California and see the drawbacks of overpermissive left turns.  there are intersections where, due to the terrain, you can clearly see that no one is coming for over a mile, and you could drive even the slowest vehicle through safely.  to gate these off is just inefficient.  certainly there's a tradeoff between "more crashes" and "more people getting through the intersection", and California I think has placed their tradeoff point well into the overcautious.

[vdeane]

If someone can't judge whether or not they can safely make a permissive left turn, IMO they shouldn't be driving.  Don't dumb down the roads for those of us who can do such things.

[tradephoric]

^It sounds like you are unwilling to acknowledge that an increased intersection crash rate would be a negative consequence of permissive-lefts.  Based on your comments, you are disregarding safety and focused entirely on reducing driver delay.  You almost seem to be suggesting that when bad drivers get in an accident, that's somehow a good thing.

[Alps]

Um... It's simple fact that permitted left turns lead to more crashes than protected-only left turns. You have no conflicting traffic when it's protected, but you do have conflicts when it's permitted. Conflicts = crashes.

you are literally correct.  however, come out to California and see the drawbacks of overpermissive left turns.  there are intersections where, due to the terrain, you can clearly see that no one is coming for over a mile, and you could drive even the slowest vehicle through safely.  to gate these off is just inefficient.  certainly there's a tradeoff between "more crashes" and "more people getting through the intersection", and California I think has placed their tradeoff point well into the overcautious.

Exactly! There is a tradeoff. But you have to acknowledge both sides exist in making your determination.

[vdeane]

^It sounds like you are unwilling to acknowledge that an increased intersection crash rate would be a negative consequence of permissive-lefts.  Based on your comments, you are disregarding safety and focused entirely on reducing driver delay.  You almost seem to be suggesting that when bad drivers get in an accident, that's somehow a good thing.

I don't think we should delay drivers to subsidize bad driving... IMO we could accomplish a goal of reducing crashes much better by increasing licensing standards.  There are a some intersections where high traffic might warrant protected-only lefts, but they're few and far between in my experience.  I have to go though one every time I drive from Rome to Rochester (thankfully I can bypass that infernal light on the reverse trip).  Every single time I'm stuck waiting at the intersection for two minutes to make the turn while there is hardly any oncoming traffic.

[hotdogPi]

Every single time I'm stuck waiting at the intersection for two minutes to make the turn while there is hardly any oncoming traffic.

Do you really always get there in the same part of the cycle?

[Scott5114]

Um... It's simple fact that permitted left turns lead to more crashes than protected-only left turns. You have no conflicting traffic when it's protected, but you do have conflicts when it's permitted. Conflicts = crashes.

you are literally correct.  however, come out to California and see the drawbacks of overpermissive left turns.  there are intersections where, due to the terrain, you can clearly see that no one is coming for over a mile, and you could drive even the slowest vehicle through safely.  to gate these off is just inefficient.  certainly there's a tradeoff between "more crashes" and "more people getting through the intersection", and California I think has placed their tradeoff point well into the overcautious.

Exactly! There is a tradeoff. But you have to acknowledge both sides exist in making your determination.

Adding to the complexity here is when traffic volumes go up enough, a permissive left actually has less throughput than a protected. A protected cycle will usually go for long enough to clear the left turn bay. But on a traffic-choked street, you might get the minimum–the one car that inches out into the intersection as it waits, then makes the turn as the signal goes yellow and oncoming traffic comes to a stop. The rest of the time it's waiting for a gap that never comes.

[Pete from Boston]

^It sounds like you are unwilling to acknowledge that an increased intersection crash rate would be a negative consequence of permissive-lefts.  Based on your comments, you are disregarding safety and focused entirely on reducing driver delay.  You almost seem to be suggesting that when bad drivers get in an accident, that's somehow a good thing.

I don't think we should delay drivers to subsidize bad driving... IMO we could accomplish a goal of reducing crashes much better by increasing licensing standards.

There's no question on the driver's test for hubris, haste, or self-importance, which are the real issue. At least aroud here, it's usually a game of chicken more than a judgement of clear right of way.  Someone turns left and decides oncoming traffic will just have to slow/stop rather than hit them.  I know people who intentionally don't slow down when confronted with this  -- the game of chicken often has more than one willing actor involved.

[vdeane]

Every single time I'm stuck waiting at the intersection for two minutes to make the turn while there is hardly any oncoming traffic.

Do you really always get there in the same part of the cycle?

Good question; I'm really not sure.  It does vary a little, but if I hit the light on a Saturday or Sunday as I usually do, I almost always have to wait a while.  It's better during the week.  It's a three phase signal, with two short phases for traffic turning left to/from the Thruway (right turning traffic has ramps - if you added a jughandle, it would be an at-grade trumpet) and one very long green for through traffic on Super 365.  My only guess is that Turning Stone has something to do with it.

^It sounds like you are unwilling to acknowledge that an increased intersection crash rate would be a negative consequence of permissive-lefts.  Based on your comments, you are disregarding safety and focused entirely on reducing driver delay.  You almost seem to be suggesting that when bad drivers get in an accident, that's somehow a good thing.

I don't think we should delay drivers to subsidize bad driving... IMO we could accomplish a goal of reducing crashes much better by increasing licensing standards.

There's no question on the driver's test for hubris, haste, or self-importance, which are the real issue. At least aroud here, it's usually a game of chicken more than a judgement of clear right of way.  Someone turns left and decides oncoming traffic will just have to slow/stop rather than hit them.  I know people who intentionally don't slow down when confronted with this  -- the game of chicken often has more than one willing actor involved.

The game of chicken should be outlawed and drivers caught playing it should face very stiff penalties.  I have no problem with getting rid of the "make your own ROW" culture that plagues many areas.

It's also criminal that the road test stays on quiet residential streets.  It should test all manner of driving situations, not only residential driving, but also downtown streets, suburban business districts, freeways, and rural highways.  Maybe make driver's ed mandatory too.  I was always taught that one should never assume that traffic on side streets will stop, that turning traffic will yield, or that drivers will actually turn if their turn signal is on.  I may not be aggressive enough in some instances because of this (generally, I won't move in any situation requiring a yield unless I can do so without affecting any other traffic at all), but at least my driving record is better than most people's.

[agentsteel53]

Adding to the complexity here is when traffic volumes go up enough, a permissive left actually has less throughput than a protected. A protected cycle will usually go for long enough to clear the left turn bay. But on a traffic-choked street, you might get the minimum–the one car that inches out into the intersection as it waits, then makes the turn as the signal goes yellow and oncoming traffic comes to a stop. The rest of the time it's waiting for a gap that never comes.

I think we've got a bug in our terminology here.  we don't have a word for "has a protected phase, and is permissive - as opposed to forbidden - at other times".

that's what I'm advocating for, and that's the tradeoff that Steve is mentioning.  it's not "permissive vs protected", it's "permissive vs forbidden".

[vdeane]

Exactly.  Permissive-only on high traffic roads is even more annoying than protected-only when there's a gap in traffic.