Small lights/motion detectors above traffic signals

There is a system that responsds to a transmitter on emergency vehicles that will give the vehicle a green light. The receptors are mounted near the traffic signal. One such system is called Opticom.

Here's a little more background on the Opticom System for your reading enjoyment.

http://www.tcmfd.com/stuff/opticom.html

While Opticom is the primary system used in some cities, it is not the only provider of traffic preemption systems. There are also:

Collision Control Communications™
MIRT™ / Stealth MVP™
Priority Green™
Tomar StrobeCom II™

In Florida, Texas and a couple more states that light is used to catch red light runners by an officer who is not in the same lane of travel as the offender.

Read here for a more detailed explanation:
http://www.startribune.com/local/west/17445314.html

It makes it safer to catch the perps for sure.

http://www.dot.state.fl.us/safety/CTST/Video%20and%20present...

Wow. Traffic accident fatalities top violent crime and murder.

Makes me wish there were retractable bollards coming up at the "stop bar" when a light changes to red

http://www.youtube.com/watch?v=mRPEW2OMIU8

Here they look like a small spotlight except that they don't have a transparent lens. They are infrared sensors used to detect when a car is waiting for a green light. The light won't change unless there is a car waiting for a green light. They can also be used to adjust the timing of the lights depending on traffic volume. The cities around here also use magnetic sensor loops in the pavement for the same thing.

Those are the major categories here on the Left coast.

Rat lights give traffic officers an indication of the state of traffic lights they couldn't see from their particular location. All the better to write you up for running a red light.

Emergency vehicle sensors have been discussed, looking for different wavelengths (colors) of light, pulse widths, repetition rates, and so on to bypas things for emergency vehicles. Some areas use similar systems for mass transit (trams/busses/etc).

A number of different technologies for traffic sensors. Low-res video is useful as it can work in low light (night time), and still be sensitive enough to spot bicycles -- the bike riding population is particularly vocal on the Left Coast, especially about having municipalities install signal sensor systems that can accurately spot bikes. Magnetic loops don't cut it -- you need to look for them.

I've only seen two types and I like them both.

One is a sensor that sees and notes my motion in a lane. Where those exist, the lights change for me on my bicycle or motorcycle, neither of which usually trip the surface sensors under the road surface.

The other type light up when an emergency vehicle is approaching. That's important where "Rights on Red" are allowed... especially blvds where an emergency vehicle may need to drive down the wrong side to get by a clogged intersection.

It is not widely known, but the Opticom system records the vehicle from which it received the command emission. Useful in accident reconstruction among other things.