Monday, April 13, 2009

Does it take someone to get killed....

Traffic engineers hear this complaint hundreds of times during their career. I think I’ve heard it about 1,000 times so far but I figure I still have 30 more years to go.

That being said we, as traffic engineers, don’t really help ourselves much when we include crashes (“accidents” is really a misnomer) as a criteria to install certain things. Take these as a few examples:

  • All-way stops 5 crashes in a 12-month period
  • Traffic signal 5 crashes in a 12-month period
  • Residential Traffic Circles (in Seattle) 3 crashes in a 24-month period


There are caveats to all of these, but you get the point.


If we were to look at the roadway system as a human body, it may make some more sense why crashes get included in these criteria. Let’s assume that you live a relatively healthy life. You eat well. You exercise occasionally. You see the doctor every once in a while. Everyday, the hundreds of systems in your body has thousands of interactions with other systems both internally and externally. Most of the time, these systems and interactions work fine. Every so often, though, things don’t go so well. You may catch a cold. You might extend yourself too much and break a bone or two. Or, something more serious like a disease may strike.


Most of the time, the hardy traffic engineers at the DOT catch a lot of problems before any one sees them. In the manner of leprechauns and elves, the elusive engineers have crews come out and cut back the trees blocking the view. They might even see the need for a sign before the inevitable citizen phone call comes in. Maybe, they might call out for a new crosswalk before the email from a city council member is in the in box.


Now, let’s take a typical example to put all of this to work. You call the Public Works Department and ask for a stop sign at the intersection next to school where your daughter goes to school. First thing the engineer is likely to do is to look up the crash history of the intersection. Why? Well, a couple of reasons, 1) it’s easy and nowadays can be pulled up on a computer screen and 2) a quick look can show if there is a potential problem. This is like when a doctor pulls up your family history and sees that your parents had diabetes and therefore, you have a higher risk of getting it too. Second, the engineer will go out and see the intersection and at the same time see how much traffic is going through the intersection, if the average driver can see traffic approaching while at the intersection, and watch how traffic behaves normally. This is the doctor’s examination. Then the engineer makes a recommendation and the stop sign may or may not be installed. It’s the diagnosis portion of the doctor appointment.


So, does this now make some sense about how the traffic engineer’s mind works? It’s not really that exciting or funny…which somewhat describes a good lot of traffic engineers.


Got a question on traffic? Drop me a line. mike@trafficmike.com

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