Episode 17 – Red Light Enforcement, Red Light Running, Clearance Intervals

Topics: Red Light Enforcement, Red Light Running, Clearance Intervals

Talking Traffic Episode 17 – Red Light Enforcement, Red Light Running, Clearance Intervals

Hello and welcome to episode 17 of talking traffic. My name is Bill Ruhsam, and I’m your host, as well as the proprietor of Talking Traffic.org. Today is March 24, 2008.

Several episodes so far have focused or touched on traffic signals. I talked about how an intersection is examined for signalization in episode 12, signal detection in episode 8, pedestrian involvement in episode 7 and some vocabulary in episode 1. As you can tell, there’s a great deal to discuss or learn when dealing with traffic signals. Today’s topic is about red light enforcement, red light running, and clearance intervals. I’d like to thank listener Chris Blum for sending me an email requesting this topic. It’s been on my list, but he encouraged me to get off my duff and do it. His exact question was, “Are [red light cameras] solely to collect money for cash strapped local govenments or are there safety reasons behind their installation?” The answer is No, they’re not *solely* for cash strapped governments and yes there are safety reasons.

First off, let me state for the record that I support video or photographic red light enforcement. I think it makes great sense. It’s intention is to increase the safety of an intersection by reducing the number of drivers who run the light. If you don’t want to receive a ticket for violating a red, just don’t run that red light. That seems logical to me, but some people I’ve…ahem.. discussed this with disagree and feel that it’s an invasion of privacy. I’m not going to argue the merits right now, I only wanted to state my position.

What is red light enforcement? Simply, to increase the safety of an intersection, it is the issuing of citations to a driver who runs a red light. This makes one wonder, “what exactly constitutes running a red light?” In the jurisdictions that I’m familiar with, you have legally entered an intersection as long as your front wheels have crossed over the stop bar during the yellow interval. I know that there are some laws that talk about people who accelerate into the intersection to beat the red, but for the purposes of today’s podcast, if your front wheels have crossed the line, you’re good to go. Keep in mind, that if you cross the stop line just before the light turns red, you’ll *see* it go red, but you’re still legal. The position of the signal light itself has nothing to do with your legal entry into the intersection.

Back to the enforcement aspects. Prior to photographic enforcement, a police officer would have to be sitting at the intersection, watching for violators, then chase them down to ticket them. This presented several difficulties: if the cops are on the near side of the intersection, the police officer will be forced to cross traffic that now has a green light in order to catch the violator. That is obviously not very safe. If they’re sitting on the far side of the intersection, they have difficulty seeing if a car is actually violating the red light, because they can’t see the signal lamps, and they’re a long way from the stop bar. Some jurisdictions assisted their officers by placing a white light on top of the traffic signal that lights when the signal is red, thus allowing them to be on the opposite side of the signal head and able to chase down a violator. Unfortunately, this didn’t fix their difficulty in seeing whether or not a red light runnier was entering the intersection legally, which meant they only ticketed really obvious violators.

Enter photographic enforcement. Cameras are set up to take a series of pictures in order to show that, one, the vehicle’s front wheels were behind the stop bar at the time the signal turned red, two, it entered the intersection after that time, and three, it then continued through. The cameras also photograph the license plate of the vehicle in order to send the citation through the mail to the owner of the vehicle.

This process removes police officers from a dangerous enforcement environment, and automates the process, thereby allowing the officers to concentrate on more important things, like actual crime.

As I’ve already mentioned, there have been objections to photographic enforcement ranging from privacy concerns, to constitutional objections, to government taxing issues. The constitutional one is the greatest hurdle, I think, the inability for a person to “confront their accuser.” This also dovetails with the fact that it might not be the owner driving the car at the time of violation.

The last objection is usually the one that receives the most media time, the claim that governments are installing these devices for purposes of revenue generation. In some respects, these claims are probably dead accurate, but I still don’t see any reason to not install red light cameras at choice intersections, as long as certain guidelines are followed.

This brings me to the topic of the clearance interval. Clearance intervals have a great deal to do with red light running and enforcement. Simply, at any signalized intersection, there are two types of clearance interval: the all red clearance and the yellow clearance. The all red clearance interval is intended to provide enough time, during which all lights are red in all directions, for a vehicle legally entering the intersection at the posted speed limit to “clear” the intersection. So, the time it takes for a cars tires to go from just in front of the stop bar, to the far side of the intersection is the all-red clearance interval. The yellow clearance interval is a bit more complicated, having to do with driver reactions and acceptable braking accelerations, but to simplify, it is intended to provide enough warning that drivers approaching the intersection can slow to a stop a the stop bar when given enough warning, and drivers who are too close are not forced to slam-stop in order to avoid violating the red light. It is this yellow clearance interval that causes the vas majority of complaints when it comes to red light enforcement.

When properly calculated and applied, the yellow interval should allow drivers to stop before violating the red. If it’s too short, drivers who rightly feel that they are too close to the intersection and moving to quickly to stop safely, may be ticketed because they were still behind the stop bar when the light turned red. A number of legislative bills have allowed the emplacement of red light cameras *as long as* the signals have been evaluated to ensure that the correct clearance intervals are being used. If they are not, and there is no documentation from the local DOT or Public Works Dept that demonstrates that they have been, then the tickets will be tossed out, or the red light camera will have never been installed.

Other objections that have been made to red light cameras include that they: don’t actually prevent collisions, in fact may increase the number of collisions at an intersection. The objectors usually state this using the phrase, “no increase in safety” at the intersection. This shows that people don’t understand why signals and other types of control devices are installed. You may recall from my earlier episode on installing signals that a traffic signal may actually increase the number of collisions at a particular intersection. This s a known fact. What is less well known, is that while the total number of collisions may go up, the types of collisions that are most severe, most likely to result in serious injuries or fatalities goes down. Angle collisions and turning collisions are the ones that are the most dangerous, and these are what the red light running cameras are designed to prevent. Rear-end collisions may rise, but those are much less severe, in general, and cars are better designed to handle them with more energy absorption during the collision.

There are other issues dealing with signal cameras, mostly having to do with how the money from the citations is spent, but mine is not a political podcast. Those sorts of discussions I’ll leave to others. I will say that when properly engineered, red light enforcement cameras make a great deal of safety sense and if you don’t want a ticket, don’t run the light.

Thanks for listening to talking traffic number 17. This episode is released under a creative commons 3.0, attribution, non commercial, no derivatives license. If you like what you hear, feel free to copy the podcast and send it to a friend, but please don’t change it, or sell it, and make sure you credit me and talking traffic.org. If you didn’t like what you heard, and think I’m the craziest traffic engineer who every spoke a podcast, I’d be delighted to hear about it, so send an email to Bill at Talking traffic.org or leave a comment on the show notes at talking traffic.org.

The music you heard was by Five Star Fall and is found on magnatune.com.

Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com

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