The 'twilight zone' of traffic costs lives at stoplight intersections

Mar 14, 2012
Driver uncertainty about how to react when a light turns yellow at an intersection is often the cause of accidents. (Photo courtesy of Oregon State University)

(PhysOrg.com) -- Hundreds of lives are being lost each year in the United States because of mistakes made in what engineers call the "dilemma zone" – that area before a stoplight intersection where the traffic light turns yellow and the driver isn't sure whether to stop or go ahead.

New research at Oregon State University will help to more precisely identify that danger zone. engineers can then use than information, along with advanced technology that can monitor the speed and location of oncoming traffic, to improve yellow-light timing and help address this problem.

When more widely implemented, this approach should help reduce driver confusion, add certainty to how intersections should be managed, and save lives.

"There are more than 30,000 traffic fatalities each year in the U.S., and about 2,000 of them occur in stoplight intersections," said David Hurwitz, an OSU assistant professor of transportation engineering. "We think those crashes can be reduced with a better understanding of exactly where the dilemma zone is and how traffic lights and other technology can be adjusted to help manage it."

Factors that lead to the problems in the dilemma zone include driving speed, distance to the stop light, driver skills, laws that vary by state, occasional scofflaws who are trying to "beat the red light," and simple confusion by drivers who want to do the right thing but aren't sure what it is.

There are many variables involved, Hurwitz said, such as vehicle speed and position. To help address that, researchers in one recent study used a tool called "fuzzy logic." This provides a way to produce more exact decisions with inexact data, which in this case can include everything from drivers with very different skill sets and reaction times to automobile speeds and road variability.

Based on their speed and proximity to an intersection, when the traffic light turns yellow a driver has to make a decision whether to stop or proceed. A driver who is some distance away usually stops; and a driver who is extremely close to the intersection usually will go ahead. Those decisions are fairly easy. But the "dilemma zone" is the area where the choice isn't so obvious, and the wrong decision can have serious, sometimes fatal consequences.

Complicating that, Hurwitz said, is that laws vary widely by state. In Oregon, for instance, the law requires that a car stop on a yellow light if it is safe to do so. In some other states, it's legal to proceed on a yellow light, and even be in the intersection during a red light, if the front axle of the vehicle crosses the stop line before the light turns red.

Different laws can contribute to different driver behaviors, and national standards do not now exist.

Stop too suddenly, and you're apt to have a rear-end collision with the vehicle behind you. Proceed or turn left when you shouldn't, and even more serious crashes can occur, including head-on and side impacts. And based on the speed limit, the length of a yellow light at an intersection can vary greatly.

"In traffic engineering, consistency and uniformity is a critical concern," Hurwitz said. "We want conscientious drivers to know what is the right thing to do. Given so many variables and differences in state law, that can be difficult."

The findings have been published in two recent studies, in research that was supported by the Vermont Agency of Transportation and the Lilo and Richard Smith Transportation Fellowship.

"We want to help drivers know whether to stop or proceed, and do it in a manner that is safe," Hurwitz said. "This approach should help accomplish that, prevent accidents and save lives."

Explore further: An eel-lectrifying future for autonomous underwater robots

More information: Study online: ir.library.oregonstate.edu/xmlui/handle/1957/28205

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User comments : 15

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Eikka
1 / 5 (1) Mar 14, 2012
Where I live, many places have smart lights that won't turn the green on for the crossing traffic until it senses that there's either no-one standing at the red lights, or they have actually stopped.

I believe it checks if there's movement while the lights are yellow, and adds a little pause after it turns the light red to see that the cars stop and clear the intersection. If the movement stops during yellow, or there isn't any, then there either aren't any cars, they've successfully stopped, or they're far back enough to brake on the reds.
gwrede
2.1 / 5 (7) Mar 14, 2012
A yellow light!! Gasp! OMG! LOL! Should I stop??? Gasp!! OMG! LOL! Now it's closer! Gas? Break? Gas? Break? OMG! LOL! Should I call Bill?? He'd know what to do! He always does! OMG! LOL! Oh crap, now it's closer! Whaddami gonna do????

At this point, this person either slams the brakes full on, or hits the pedal to the medal to run away. In either case, he is the one you are looking for. Personally, I think such people should never get a license! There are so many other ways they cause accidents, too.
Mayday
3.4 / 5 (5) Mar 14, 2012
I am always surprised at how hard many people work at maintaining such a low driving proficiency. There are many who drive an hour or two each day. If I played piano or even trombone for an hour or two every day, after a few decades I trust that I would be quite good. IMO, persistent bad driving takes concerted commitment. I'd rather just drive well.
dogbert
1 / 5 (4) Mar 14, 2012
Factors that lead to the problems in the dilemma zone include driving speed, distance to the stop light, driver skills, laws that vary by state, occasional scofflaws who are trying to "beat the red light," and simple confusion by drivers who want to do the right thing but aren't sure what it is.


A primary factor which is not even mentioned in the article is the deliberately shortened times for yellow lights which allows the municipality to issue traffic citations to citizens who are unable to stop due to the shortened yellow light timing.

Fortunately, such municipalities generally delay the green light on the other lanes because of the shortened yellow light timing.
DirtySquirties
3 / 5 (2) Mar 14, 2012
I think it's just too much of a guessing game as is.
I'd like a timer to see how long I've got until red turns green and vice versa. Some crosswalks have pedestrian count downs and I have used those to gauge ahead of time whether I should speed up a bit to get through the green/yellow or give up and start coasting. I love that, I would be able to coast up to lights or confidently go through them more often and save me some gas.
RitchieGuy
1 / 5 (2) Mar 14, 2012
LOL. . .people behind a car that's coasting up to a redlight get pissed off. Sometimes they'll even pass you in order to get to the red ight ahead of you. I laugh whenever I see that because they usually are in such a rush that they have to slam on their brakes because the light didn't turn green fast enough for them.
I coast to a red light and at times, if you know the area well, you can time the cycle from amber to red to green and get there just as the light turns green so you don't have to brake at all.
I look at some of those who are in a big hurry and I see road rage.
Hengine
5 / 5 (1) Mar 14, 2012
In the UK the amber light is lit alone when it's about to turn red.

When the light is about to go green the amber blinks.
Hengine
5 / 5 (1) Mar 14, 2012
Sorry. There is a combination of red and amber prior to the light going green. I'm bad at remembering details like this but I never find myself confused on the road.
scidog
not rated yet Mar 15, 2012
some lights around us have count down timers for the crosswalks.
i know keeping a eye on the timer.it's big and easy to see,for the person crossing the street could be a distraction for a driver but it tells me as i come up to the light how much time i have before it chances.
MediocreSmoke
1 / 5 (1) Mar 15, 2012
LOL. . .people behind a car that's coasting up to a redlight get pissed off. Sometimes they'll even pass you in order to get to the red ight ahead of you. I laugh whenever I see that because they usually are in such a rush that they have to slam on their brakes because the light didn't turn green fast enough for them.
I coast to a red light and at times, if you know the area well, you can time the cycle from amber to red to green and get there just as the light turns green so you don't have to brake at all.
I look at some of those who are in a big hurry and I see road rage.


I'm not sure why you driving slowly up to red lights, and probably in general, is relevant to yellow lights being dangerously ambiguous. I think it more than likely that you have road rage, whether or not you make people upset behind you.

I think a lot of what this article is saying is that there isn't a standard nationally, where there should be one.
Vendicar_Decarian
5 / 5 (2) Mar 15, 2012
"I'd like a timer to see how long I've got until red turns green and vice versa." - Dirty

That would be my preference as well, but it may cause even more harm since people with vision problems who can easily see existing lights may not have the visual acuity to see a graph or number.

Misinterpretation of a more complex system may cause more accidents than it solves.

There should be standards for the duration of yellows as well as standard symbols for when it is clear to turn across the oncoming lane at an intersection.

In my area advanced green is not always used to indicate that the oncoming lane still has a red when the containing lane has a green. Neither are there standard positions for left turning lights or even lights for specific lanes.

There is always some question as to which light represents which condition and if a green actually allows movement through an intersection without causing problems.

Anywhere there is ambiguity there will be accidents.
unknownorgin
2.3 / 5 (3) Mar 15, 2012
In california stop lights are set to change from green to red rapidly for the purpose of generating revenue with the red light cameras. Acidents and injury caused by Quick change traffic lights are of no concern to local governments in the quest for the mighty dollar.
SteveMerrick
not rated yet Mar 15, 2012
This article highlights the fundamental safety problem with traffic lights, and does/says nothing about how it can be improved. Shame.
alq131
not rated yet Mar 15, 2012
The day will come when *OnStar* or some such system will talk with the traffic lights. The red light will stop your car for you...no need to think.

In many places there are additional "white lights" at traffic intersections. These blink when emergency vehicles take control of the stoplight system giving them a green and all others red. This system is abused too by people buying encoder/transmitters to give themselves a green...maybe this could be incorporated into a smart system where users pay a toll to always have a green light, this would offset the cost of the car always stopping at a red if under supervisory control. ;)
Justin_Bowman
5 / 5 (2) Mar 15, 2012
The Koreans figured this problem out years ago. They have two sets of lights, one at the intersection and one at the edge of the dilemma zone. If the signal changes to yellow before you reach the first set you stop, otherwise you keep going. This also allows for clear-cut rulings for red light cameras so municipalities can subsidize the cost of adding the new hardware with their ticket revenues.

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