Slashdot Mirror
Traffic Light Switcher Makes Critics See Red
An anonymous reader writes "According to a Yahoo/Washington Post article: 'It sounds like a suffering commuter's dream come true: a dashboard device that changes red traffic lights to green at the touch of a button.
Police, fire and rescue vehicles have had access to such equipment for years, but now the devices are becoming available to ordinary motorists
thanks to advances in technology and a little help from the Internet. Safety advocates are outraged, and news accounts in Michigan last week
led to politicians there seeking a ban on the gadgets'." Update: 11/06 02:25 GMT by S : A previous Slashdot story mentions the device, though not the Michigan legislature's subsequent ire.
FCC controls RF, nobody controls light (IR)
They are on sale here
Some lights have video cameras on them for this very purpose. They're programmed to tell how far back the cars are lined up based on the contrast between a car and the road. They have the added benefit of catching those who run red lights.
They already do that. They're called proximity detectors, and they determine when cars are sitting on top of them. They work based on induction.
Sometimes you can see where they were embedded in the road, especially if the light was retrofitted. Look for a patched-over hole in the pavement directly underneath where the first car would pull up at a stop light.
That is why some lights only change when your car is sitting there. For additional fun, you might be caught behind some dingus who, for some reason, stopped too far back to trigger the sensor. You're going to be there a while.
Toronto-area transit rider? Rate your ride.
Explanation of Traffic Signal Preemption (Stoplight Changing)
The normal operation of any traffic signal controlled intersection is designed for the maximum and efficient throughput of vehicular traffic.
Unfortunately, a common occurrence at any intersection is traffic back-up, which can require many signaling cycles to clear. Without the ability to change the operation of the traffic signals themselves, police and emergency response vehicles can also be forced to sit in traffic, thus dramatically increasing their response times to crime scenes and fire or medical emergencies.
Furthermore, even without heavy traffic, a police or emergency response vehicle entering a traffic signal controlled intersection at a high rate of speed places all motorists (and sometimes pedestrians) at extreme risk.
The MIRT is an optical communications system that allows equipped vehicles to alter the normal operation of traffic signals.
An overview of a typical scenario is as follows:
A fire truck is dispatched to an emergency.
The fire truck is equipped with multiple emergency warning lights and a siren... The fire truck is also equipped with a preemption transmitter, which, in operation, is a high intensity forward-facing strobe light that is flashing at a rapid rate - much faster than normal attention-getting lights on the fire truck.
When the fire truck approaches within 1,800 feet (line-of-sight) of a preemption-equipped traffic signal controlled intersection, the preemption detector (normally mounted on the cross-arm that suspends the traffic signal) "sees" the fire truck's preemption transmitter and locks onto its flashing strobe.
Once the traffic signal "sees" the fire truck, it begins to initiate a "preemption sequence" of the actual traffic signal that is different from normal operation.
If the fire truck already has a green light, the light will remain green. Any other direction that also has a green light (usually the opposite direction) will first get a yellow light, then red.
When all of the other directions are then red, and the fire truck's direction is the only one that is green, the left turn arrow will illuminate (if one exists), and a brilliant white flood lamp mounted near the traffic signal will begin to flash. This flood lamp tells the driver of the fire truck that he now has control of the intersection, and complete right-of-way.
If the fire truck has a red light, any other direction that has a green light will transition to yellow, then red. When all the directions (including the fire truck's) are red, the traffic signal facing the fire truck will then turn green, along with the left turn arrow (if one exists), and the brilliant white flood lamp will begin to flash.
Once the fire truck has passed through the intersection, optical communication with the preemption detector (on the traffic signal) is lost. At that time the traffic signal will default back to normal operation. Conversely, until the fire truck passes through the intersection, it will have a green light, regardless of the time duration.
If several intersections are within the 1,800 foot range of the fire truck's preemption transmitter, they will all respond accordingly to the above operational description.