Gotta go, head hurts…

Let’s Keep ‘Er Movin’

Traffic Guy
(Honorary Trafficologist)

PS. in case anyone else is wondering who the heck we’re talking about, check out the WRAL video feed at
http://www.wral.com/video/index.html
and click on
“Work To Repair Portion Of I-40 Slated For Friday”
to hear Mr. Robert’s dulcet tones (after the segment intro)
(his bio is at http://www.wral.com/staff/460839/detail.html if you’re REALLY looking to duck productivity today)

BTW, I just KNEW there was a conspiracy. Now maybe I can be an honorary member of the Lone Gunmen…well before that “Jump the Shark” episode that is.

Auggggh! (Insert Charlie Brown head smack)

I can’t stand that guy! He provides a valuable service to the area and does his job well, but his delivery is like nails on a chalkboard to me…

I’m actually a techie who worked for several years in the Signals Management Unit of the North Carolina Department of Transporation, and still do a lot of consulting in the field.

By the way, I do recall from my years there a “Jeff Wooten” being on the special “detect and impede” list, and there was a company working on a prototype detector that would scan driver’s retinal movements and switch to green when no one is looking so as to prompt a lot of honking and bird-flipping. There wasn’t a lot of interest at the time, but perhaps that’s changed…

In order to avoid any more confusing, let’s just shorten my moniker to Traffic Guy! When you need me, just shine an alternating red, amber, and green light in the air…

BTW (and slightly off topic), Mark the Traffic Guy, You mentioned Raleigh in an earlier post. I live near Raleigh too, so my curiosity is working overtime: You’re not Mark Roberts the WRAL-TV traffic reporter are you?

The detector won’t be in the light, though. It’s probably mounted to one of the nearby poles.

There are even detector systems that detect special strobe flashes from oncoming emergency vehicles to give the vehicle the quick right-of-way.

By the way, I enjoy the heck out of your blog. Always keeps me and the guys at work entertained with what you find on the net. (You, and boingboing.net). Thanks!

Now, do any of these systems use radar? There are some lights in the town next door to me that cause my radar detector to pin at the highest possible level. It’s only at the traffic lights that this happens. I’ve suspected that the lights have little detectors to see when cars are near, using radar. Am I that far off?

Traffic signals are typically controlled by several pieces of equipment inside a metal cabinet installed at one corner of the intersection, including a controller, which is a microprocessor that runs the timing patterns and special programs that illuminate the traffic signals and pedestrian signals. The intersection can be run in different modes:

-Pre-timed modes - where the signals run according to special timed patterns. This is common in urban intersections where there is always a large amount of traffic. Controllers can also run different patterns at different times of the day to reflect changes in traffic density at say, rush hour vs. mid-morning.

-”Actuated” modes - where the signal timing patterns are affected or triggered by traffic detectors. (present-day controllers are smart enough to change the timing patterns continuously based on how much traffic is detected)

By far the most popular form of traffic detection is the Inductive Loop Detector. Those “scar marks on the road” are small rectangular trenches cut into the asphalt. A special cable is laid into the trench and looped around (anywhere from 2 to 6 times), then covered with sealant. Both ends of the cable are run back to the controller cabinet and connected to an Inductive Loop Detector. This detector sends a electrical current through the cable. This current creates a magnetic field that extends from the road level to 1 or 2 feet above the roadway. When a large metal mass (like a car) passes over the loops, this magnetic field changes. The detector senses the change in the field and sends a signal to the controller, saying in effect “There’s a car here!” The controller then runs a timing pattern to change the signals to give the car “the green light”.

So, it doesn’t have anything to do with the weight of the vehicle. Its operation also explains why motorcycles and large trucks are sometimes not detected. Motorcycles may either not be positioned directly over the loop nor have enough metal to change the magnetic field enough to be detected (tell your biker friends to put their bikes directly over the loop for the best chance). Large trucks have a large metal mass, but the truck bodies may be so far above the road that they do not change the field.

There we go. Sorry you asked, yet?

Lemme know.

You can also go to a website run by a fellow Raleigh-ite (Raleigh-onian? Ral-lite?): http://auto.howstuffworks.com/question234.htm

Great site that you can waste hours in.