Emergency Sirens Will Trigger Green Light

The same technology that makes weather radar work is also helping Cheney firefighters get to calls more safely.

The state Department of Transportation recently installed an emergency signal-control device at the intersection of state Highway 904 and the Cheney-Spokane Road.

It is the first device of its kind installed on a state-owned highway in a trial program, said Al Gilson, spokesman for the Transportation Department in Spokane.

Sirens from police cars, ambulances and fire trucks can be detected by the device, which then turns the signal red in all other directions. The light goes green for the emergency vehicle and any other cars ahead of it.

As a result, emergency vehicles can then pass through the intersection more quickly and safely.

The new system employs Doppler-effect technology, which allows a computer to determine the direction of the approaching siren.

Doppler radar is now being used by the National Weather Service to monitor the movement of storms around the country. Doppler simply determines the direction of movement, whether it’s a storm cloud or a racing siren.

Microphones are mounted on the traffic light poles to pick up the sound of the approaching sirens. The siren frequency and the direction from which it is coming are picked up by the computer. The computer then pre-empts traffic in other directions.

Until now, pre-emption systems worked either by a radio signal sent by emergency drivers or by a strobe light mounted on emergency rigs.

But those systems require both the signal and emergency vehicles to be fitted with compatible equipment, Gilson said.

The new Doppler sound technology works on its own without any additional equipment on the emergency vehicles.

The Doppler systems are manufactured by Sonic Systems Corp. of Vancouver, B.C., and cost about $4,800 per signal.

“As far as its capability, I like it,” said Fire Chief John Montague in Cheney.

Montague said the system has a small acknowledgment light attached to the signal pole that lets emergency drivers know that the pre-emption system has been activated.

Montague said the state should set the acknowledgment light so that it comes on as soon as the computer picks up the approaching siren. That would give drivers more confidence in approaching the intersection, he said.

Gilson said the Cheney intersection was chosen for the test because it is fairly close to the state’s regional sign shop in Spokane and the intersection does not carry a heavy volume of traffic.

If the system works, the state might purchase more such systems in the future, he said.

, DataTimes