You’re rushing home on North Florida. Traffic moves well since I-4 construction ended. You’re almost to the intersection as the light turns yellow.
One second: You check traffic in the intersection. Clear, you can keep going.
Two seconds: You check your speed. At the limit, but you can safely stop.
Three seconds: You check your rear-view mirror. Where did that speeding truck come from?!
What do you do? Should you stay or should you go?
You gun the engine and barely make it through. The truck stays right on your tail. The light is red before you make it through. The truck isn’t even close.
You just left The Dilemma Zone. That time where you decide to continue through the intersection or hit your brakes. Traffic engineers have completed numerous studies to predict how you’ll act in the zone of indecision.
Proponents of Red Light Cameras believe many drivers decide too late or simply run the red light. Opponents claim if you lengthen the yellow light duration, fewer drivers will run red lights. RLC proponents counter-claim drivers get used to the new longer yellow light and continue running red lights.
Studies abound proving both sides are correct. It just depends on which study you believe asked the right questions. At the end of this column, I’ll list links for both sides. Read them and make your own decision.
Here’s the primary question most want answered: What’s the priority — traffic flow or safety? Traffic Engineers want to move traffic with a minimum of accidents. None would be best, but they’re dealing with imperfect drivers. Since the 1930s, as traffic has increased, engineers have tweaked traffic signals. The following describes one method to shorten yellow light duration and/or eliminate all red intersection time:
(1) I’m traveling on South Florida. I see the light turn yellow. You’re on Patterson waiting on red. You watch me go through. The light stays yellow for a long time and goes red after I pass. The driver behind me stops at the red. Both lights are red for a bit. Then your light turns green. You’re bored.
(2) Same cars. Same drivers. Same positions. This time the guy behind me runs the red. The yellow duration was a little shorter. Believe it or not, traffic engineers planned that he’d do so. They’re trying to get more cars through the intersection as lights are timed the length of South Florida. You get your green light a second later and pull out on his heels. You think he shouldn’t have run the red light. This time you’re a little irritated.
(3) One last time before this gets tedious. Same cars. Same drivers. Same positions. The yellow is very short. This time you get the green instantaneously with his getting the red. You can’t go because he’s traveling through the intersection. You lose a little green waiting for him to clear the intersection. Now when you pull out, you’re angry.
The idea behind each of those three scenarios was to keep traffic flowing as streets got busier. Yellow light duration is tied to expected traffic speed. Speed limits are set to follow the 85th percentile rule, “Vehicles traveling over the 85th percentile speed (or faster than the flow of traffic) have a significantly higher crash risk than vehicles traveling around or modestly below this speed.”
Driving around Lakeland, I don’t get the impression we have a lot of short duration yellow lights. I conducted a completely non-scientific study at two intersections yesterday. I took a stop-watch to the corner of North Florida and Sleepy Hill Road. Drivers heading South on Florida had an average of 4.90 seconds to clear that intersection. Drivers turning from Sleepy Hill onto Florida had an average 3.86 seconds to clear the intersection. That make sense. They’re going slower.
I moved down to South Florida and Patterson. See that little intersection in the middle of the map? South Florida drivers had an average of 3.85 seconds to clear that intersection. Patterson drivers, when they finally got to go, had about 3.75 seconds to clear the intersection.
In the time I spent yesterday, near rush hour, no one ran a red light. No one was even close. We know that’s not always the case, and a lot of studies try to find out why drivers run red lights.
In a 2001 study sponsored by the Texas Department of Transportation (pdf), red light violations were either “avoidable” — drivers ran red lights even though they felt they had time to stop, or “unavoidable and intentional” — the driver didn’t believe he could safely stop, or “unavoidable and unintentional” — he was simply unaware of the red light.
The study stated “avoidable” violations pointed to a disrespect of the law and only increased enforcement reduced this problem. This problem is where we get the call for more traffic officers and RLCs.
“Unavoidable and unintentional” red light runners simply missed the light. It could be too high, too low, off on one side, and a myriad of other problems. Improving signage helps this problem.
“Unavoidable and intentional” drivers were best helped by increasing the yellow light duration an extra .5 to 1.5 seconds. These drivers account for the majority of “red light violations” and increasing yellow duration reduced violations about 50 per-cent. The study concluded drivers did adapt to the longer yellow, but that didn’t undo the benefit of the increase.
Guess where most accidents happen? That’s right — “Unavoidable and unintentional.” The help for that problem isn’t greater enforcement nor increased yellow. That problem is reduced by “a comprehensive engineering analysis of traffic conditions, control device visibility, and intersection sight distance.”
In short-hand: call out the traffic engineers if you want to reduce crashes, increase yellow to reduce violations, and use RLCs merely to catch the scofflaws in the act.
According to the Lakeland Police Department, Lakeland Traffic Operations is studying increasing yellow light duration at select intersections. LTO evidently is actually testing select intersections by increasing yellow duration.
The city is also tracking the 10 greatest problem intersections. LPD traffic officers see the top 10 listed each morning on their intranet. They can then target those intersections for enforcement.
I have to give TBO and LPD high marks for not waiting for the RLC decision to be resolved. Both departments are trying camera-free solutions first. I hope the studies continue even if the city gives the go-ahead to the cameras. Before we sign the first contract, we should study each major, or problem intersection. Then increase yellow duration if needed. Visibility problems should be addressed. Then, and only then, should the city work with an RLC company to determine where to install cameras.
Effect of Yellow Interval Timing On Red Light Violation Frequency At Urban Intersections (pdf)
The Red Light Running Crisis: Is it Intentional? (pdf)
Development of Guidelines for Identifying and Treating Locations with a Red-Light-Running Problem (pdf)
AAA Michigan Study Synopsis (pdf)
Effectiveness of Dynamic Speed Display Signs in Permanent Applications (pdf)
Traffic Analysis Tools (html)
Manual on Uniform Traffic Control Devices (html)
Traffic Signal Operations – Signal Timing and and Intersection Design (Links to various publications.)
An interesting give and take on increasing yellow light duration…