Should Cities Help Drivers Hit Green Lights All the Time?

[cpzilliacus]

Atlantic Cities: Should Cities Help Drivers Hit Green Lights All the Time?

There's plenty of "smart" traffic light innovation going around these days. But if you're perpetually stuck in traffic, the smartest light is surely the one that turns green right when you get there. Traffic Light Assist, a product German automaker Audi showcased at the Consumer Electronics Show in Las Vegas earlier this month, comes with the promise that hitting the green light, every time, could one day be a reality.

Combining data from a city's traffic signal infrastructure and the car itself, Traffic Light Assist shows the driver a countdown clock to green as well as what speed to drive at to make the next green light, all in a dashboard display. Audi claims that by making traffic flow more efficiently, TLA can help cut down on carbon emissions as well.

[1995hoo]

Every time I've driven in the UK I've wished the US would allow the combined red-yellow cycle that comes on prior to the green light (I know this is used in other countries as well, but I cite the UK because it's the one in which I've driven the most). The American omission of that cycle means that unless you either know the light really well or you watch the signal for the other road (the correct signal head, in many cases), you have no idea when the light is about to turn, and it results in the inevitable delay waiting for people to get moving (especially the mobile-phone users, which is a growing problem that the additional cycle might not solve). When I leave my neighborhood, the stop bar at the light is set over a car length back from the other road. I watch the light for the other road and when it goes yellow, I shift into first gear and start easing off the clutch so the car is already rolling by the time my green arrow comes on. Can't do that at all lights, of course, but it sure would be nice if there were a better way to know when the green is about to come on.

[cpzilliacus]

Every time I've driven in the UK I've wished the US would allow the combined red-yellow cycle that comes on prior to the green light (I know this is used in other countries as well, but I cite the UK because it's the one in which I've driven the most).

Finland has this at certain intersections as well, including protected left turns.

The American omission of that cycle means that unless you either know the light really well or you watch the signal for the other road (the correct signal head, in many cases), you have no idea when the light is about to turn, and it results in the inevitable delay waiting for people to get moving (especially the mobile-phone users, which is a growing problem that the additional cycle might not solve). When I leave my neighborhood, the stop bar at the light is set over a car length back from the other road. I watch the light for the other road and when it goes yellow, I shift into first gear and start easing off the clutch so the car is already rolling by the time my green arrow comes on. Can't do that at all lights, of course, but it sure would be nice if there were a better way to know when the green is about to come on.

Only issue I would see with this is pedestrian and bicyclist safety. 

In California, where the driving "culture" is to be very good about yielding to pedestrians, this would be a great idea.  In the UK (at least in the part of England around London) drivers are similarly very polite to pedestrians (and as I have stated before, I have not dared to drive in Britain, but I have walked there - a lot - and ridden many submodes of transit).

In many metropolitan areas of the Eastern U.S. (including specifically Washington and Baltimore), I believe it might make for more vehicle crashes involving peds where the motorist is at fault.

[briantroutman]

The American omission of that cycle means that unless you either know the light really well or you watch the signal for the other road (the correct signal head, in many cases), you have no idea when the light is about to turn...it sure would be nice if there were a better way to know when the green is about to come on.

Luckily, the combination of ped and vehicle signals at most standard four-way intersections in San Francisco largely accomplish this already.

The cycle goes: Light facing you is green. Ped countdown (facing your direction) goes to zero; vehicle signal immediately turns yellow, then red.

And when the light you're approaching is currently red, in many cases, you can see the ped signal facing the perpendicular direction going from flashing to solid, indicating that the cross street light is turning red and your direction will soon have green.

It has saved me endless frustration trying to beat lights in futility or losing momentum on a red light that's about to change. There are a few lights which are exceptions to the pattern, but you quickly learn which they are.

[Brandon]

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.

[wxfree]

Here in the Fort Worth area a new toll road is being built from Fort Worth to Cleburne.  The highway to southwest Fort Worth is certainly warranted, but extending it to Cleburne seems like a waste of money.  SH 174 already connects there.  It has a minimum of four lanes, with six through the towns.  If they could time the signals so traffic didn't have consecutive red lights so frequently (at least where the signals are close together), they could save a bunch of money on the unneeded highway extension.  Of course, now that the toll road is being built, I wouldn't be surprised if they put up more signals and found some way to time them even worse.

[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.

*By "on that section," I mean I may have to stop at red lights on the portions either immediately south of or north of the paired one-way section, but I can make it through the entire one-way portion without stopping. On northbound trips I can't remember the last time I didn't have to stop at the light at Duke Street right as the one-way portion begins.

[hotdogPi]

I just think they need to time it right.

(However, it seems impossible to time it right in both directions.)

[Brandon]

I just think they need to time it right.

(However, it seems impossible to time it right in both directions.)

If they were smart, they'd dump the left turn lanes and build more roads like Telegraph Road.

[tradephoric]

Here's a demonstration video of the technology in action along Telegraph Road.

[tradephoric]

Every time I've driven in the UK I've wished the US would allow the combined red-yellow cycle that comes on prior to the green light (I know this is used in other countries as well, but I cite the UK because it's the one in which I've driven the most). The American omission of that cycle means that unless you either know the light really well or you watch the signal for the other road (the correct signal head, in many cases), you have no idea when the light is about to turn, and it results in the inevitable delay waiting for people to get moving (especially the mobile-phone users, which is a growing problem that the additional cycle might not solve). When I leave my neighborhood, the stop bar at the light is set over a car length back from the other road. I watch the light for the other road and when it goes yellow, I shift into first gear and start easing off the clutch so the car is already rolling by the time my green arrow comes on. Can't do that at all lights, of course, but it sure would be nice if there were a better way to know when the green is about to come on.

I mentioned this study before, but it compares intersections in Malaysia both before and after the installation of count down signals.  The study found that the installation of count down timers had no effect on increasing throughput.  That being said, I have seen many clueless drivers completely miss a left-turn phase because they weren't paying attention to the signal.  The Malaysia study did find that the use of count down signals dramatically reduced the occurrence of red light runners.

http://www.easts.info/on-line/proceedings_05/1301.pdf

By the way, count down timers can be used at adaptive traffic signals.  In order to maintain coordination, the signals along an adaptive corridor must have a known "pulse"  point.  This pulse point is almost always at the termination of the main-street green.  Drivers on the major corridor would know exactly when the signal is going to change from green to red, even if the signals are running adaptive.  However, drivers on the side-street wouldn't known when their phase is ending since that phase is usually allowed to gap out early.  In addition, drivers waiting at a red light on the major corridor wouldn't know when they are going to get a green until the side-street termination begins (but then the countdown timer could start when the side-street starts running its clearance intervals... so drivers on the main corridor could get roughly a 6 second heads-up that the light is about to change from red to green).   I hope that makes sense!

[Indyroads]

Isnt this the point o fITS corridors to keep traffic moving as much as possible on the major thoroughfares.


I remember how on Madison Ave in Sac County they had synchronized the signals from I-80 to Sunrise Blvd to keep traffic moving. You only usually had to stop about 4-5 times in the 15 signals between the two major intersections.

[M3019C LPS20]

Every time I've driven in the UK I've wished the US would allow the combined red-yellow cycle that comes on prior to the green light.

Back in the old days here in various parts of the United States, traffic signals used to display that particular overlap you mentioned in your comment. There was also a green/amber overlap, but the meaning was the total opposite. It indicated to a motorist to slow down and come to a full stop, since the red signal indication appeared lit after this overlap terminated.

Of course, times have changed, and, with that said, standards in traffic control have changed as well.

[US71]

Some towns use traffic signals for slowing traffic.  Or in the case of Springfield, MO, as cash cows (for those who remember Red Light Cameras)

[GaryV]

Some towns use traffic signals for slowing traffic. 

Yup.  The speed limit is 35, but if you go 35 you get stopped by the lights at the minor intersections.

Until you realize that if you go 45, you'll beat the light.

So what happened to the traffic calming now?

[Brandon]

Some towns use traffic signals for slowing traffic. 

Yup.  The speed limit is 35, but if you go 35 you get stopped by the lights at the minor intersections.

Until you realize that if you go 45, you'll beat the light.

So what happened to the traffic calming now?

It's called "the law of unintended consequences".  These morons thought that by stopping traffic at the signals they'd calm traffic.  Instead, traffic wised up to their game and goes faster to compensate for the poorly timed signalization.  It's why we have a lot of speeding between signals in northeast Illinois and a lot of red light running.

[Mdcastle]

The American omission of that cycle means that unless you either know the light really well or you watch the signal for the other road (the correct signal head, in many cases), you have no idea when the light is about to turn...it sure would be nice if there were a better way to know when the green is about to come on.

Luckily, the combination of ped and vehicle signals at most standard four-way intersections in San Francisco largely accomplish this already.

The cycle goes: Light facing you is green. Ped countdown (facing your direction) goes to zero; vehicle signal immediately turns yellow, then red.

And when the light you're approaching is currently red, in many cases, you can see the ped signal facing the perpendicular direction going from flashing to solid, indicating that the cross street light is turning red and your direction will soon have green.

It has saved me endless frustration trying to beat lights in futility or losing momentum on a red light that's about to change. There are a few lights which are exceptions to the pattern, but you quickly learn which they are.

That's one thing I liked about driving in the Bay Area. It seemed the countdowns were everywhere and they all went on with the green light whether there were any pedestrians there or not. As I posted before if really tripped me up when I drove into Oregon, and started slowing down way down when the counter reached zero anticipating a red, pissing off a  truck driver behind me.

[Duke87]

This seems needlessly complicated and needlessly distracting.

I'm going to have to echo the sentiment of "just time the lights better, dummy".

[cpzilliacus]

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.

[cpzilliacus]

It's called "the law of unintended consequences".  These morons thought that by stopping traffic at the signals they'd calm traffic.  Instead, traffic wised up to their game and goes faster to compensate for the poorly timed signalization.  It's why we have a lot of speeding between signals in northeast Illinois and a lot of red light running.

Many (most?) streets in the District of Columbia feature signalized intersections that could (or should) be re-timed.  But people that drive those streets regularly know how much over the posted speed limit they have drive to "make" the green phase in signalized intersections.

[tradephoric]

This seems needlessly complicated and needlessly distracting.

I'm going to have to echo the sentiment of "just time the lights better, dummy".

It's easy to say just time the lights better.  The problem is most 2-way roads have closely spaced and irregularly spaced traffic signals.  These two factors ruin the potential for good 2-way progression.  The best ITS system in the world isn't going to fix bad geometrics. 

[1995hoo]

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.

....

That's my experience too, and I don't know why it works out that way either. I do find I'm often able to maintain a slightly higher speed on the southbound trip (why, I don't know) and maybe that contributes to it, as I'll usually be hitting a couple of the lights during the final ten seconds before they change (this based on noticing the pedestrian countdown signals, all of which hit zero right as the light goes yellow). Slowing down even a little bit would thus probably make me hit a red somewhere–usually at King Street or Prince Street, it seems.

It's called "the law of unintended consequences".  These morons thought that by stopping traffic at the signals they'd calm traffic.  Instead, traffic wised up to their game and goes faster to compensate for the poorly timed signalization.  It's why we have a lot of speeding between signals in northeast Illinois and a lot of red light running.

Many (most?) streets in the District of Columbia feature signalized intersections that could (or should) be re-timed.  But people that drive those streets regularly know how much over the posted speed limit they have drive to "make" the green phase in signalized intersections.

No doubt the District's response would be not to re-time the lights but rather to throw up more speed cameras set to a minimal tolerance.



One of the problems nowadays with trying to hit a series of green lights is the delay you encounter in getting started in the first place. So many people don't pay attention and don't move when the light goes green because they're focused on other things like playing with mobile phones, doing their makeup, digging in the glovebox, etc. This morning was a rare instance where I didn't have to beep the horn to get someone ahead of me to start moving at a green light.

The other thing I've noticed at traffic lights lately doesn't necessarily contribute to getting through a series of lights or not getting through, but it's still darn annoying, especially if you're trying to get into a turn lane. I've noticed people seem to leave way more space than they used to. I find it's not unusual to see full carlength spaces being left open. No doubt some of this comes from people who don't move up when the cars in front of them move; as a manual-shift driver I understand that, although if there were a full carlength I'd roll forward. But I see a lot of people who come to a stop really early and prematurely, leaving a huge gap. I don't understand it. I know 20 years ago or so there was a lot of publicity about carjackings in some places and there were suggestions that people should try to leave some space for an "escape route," but you don't hear much about carjackings these days, and in any event if you're in traffic leaving an "escape route" is futile.

I suppose the huge gaps may well contribute to people not getting through lights when you're in heavy traffic because it results in you being further back on the road than you might otherwise be, such that you wind up stopping before a light rather than getting across the intersection. Last Thursday morning I couldn't make it across an intersection, so I stopped rather than block the box....the obnoxious woman behind me started blowing her horn at me and pointing at the green light.    I half-expected her to try to get around me and cut back in and block the box.

Look at the sizes of the gaps people were leaving here (click to play video). Since there's no dedicated turn lane at the next light, I took advantage of one of the gaps.

[jeffandnicole]

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.

It happens often: Widen or improve a highway, and motorists will often change their commute to use that highway.  But then the environmentilists, NIMBYs, anti-highway/pro-mass transit crowd pipes up saying that the highway improvement didn't work and already filled up with cars.

While it's partially true, DOTs and others need to point out that alternative routes - which are often residential or really meant for local traffic - are less crowded.  Thus, the locals are able to get around better, and the longer-distance traffic is kept on the highway.

And, on the widened highway, the congestion doesn't last as long.  Instead of congestion going for 3 hours, maybe it only occurs for 1 hour. 

[tradephoric]

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.

....

That's my experience too, and I don't know why it works out that way either. I do find I'm often able to maintain a slightly higher speed on the southbound trip (why, I don't know) and maybe that contributes to it, as I'll usually be hitting a couple of the lights during the final ten seconds before they change (this based on noticing the pedestrian countdown signals, all of which hit zero right as the light goes yellow). Slowing down even a little bit would thus probably make me hit a red somewhere–usually at King Street or Prince Street, it seems.

The default simulation models in Synchro assume that some drivers are exceeding the speed limit by as much as 15% of the actual link speed.  Of course it goes the other way too, where some drivers are only going 85% of the link speed. I would say timing a corridor for 5 mph over the speed limit may help reduce the number of "soft stops" drivers experience. This might help cut down on the number of rear-end accidents. 

[1995hoo]

What do you mean by "soft stops"?