Phoenix-area drivers are used to seeing freeway entrance-ramp
meters with alternating green and red traffic lights during weekday rush hours.
But some of the red lights in Interstate 17 ramp meters also play a role as
part of the pilot wrong-way vehicle detection system being tested by the
Arizona Department of Transportation.
When a wrong-way vehicle is detected by the thermal
camera-based technology now in place along 15 miles of I-17 in Phoenix, the
system also turns on the red lights in nearby entrance ramp meters to try to
hold “right-way” traffic from entering the freeway.
“While most drivers aren’t used to seeing a solid red
light displayed by a ramp meter for more than a few seconds, we want I-17
drivers in Phoenix to know there is a reason for that to happen – a wrong-way
vehicle may be ahead on the freeway,” said Susan Anderson, ADOT’s systems
technology group manager.
Via the I-17 pilot project’s decision support system, the
red lights on entrance ramp meters are programmed to turn on within 3 miles of
a detected wrong-way vehicle. If the vehicle continues along the freeway,
additional ramp meter red lights will be activated. The red lights are
programmed to return to their normal mode for that particular time of day or
night, including turning off, after the system detects that the wrong-way
vehicle is no longer in the area.
“As we test the overall wrong-way vehicle alert system
and research its performance over the next several months, it’s important to
note that the ramp meter red lights are one of several countermeasures,”
Anderson said. “The ramp meter lights are traffic signals, so I-17 drivers on
entrance ramps should be prepared to stop if the light is a solid red, no
matter what time of day.”
The first-in-the-nation I-17 system features 90 thermal
detection cameras positioned above exit ramps as well as the mainline of the
freeway between the I-10 “Stack” interchange near downtown and the Loop 101
interchange in north Phoenix. When a wrong-way vehicle is detected entering an
off-ramp, the system is designed to trigger a background-illuminated
“wrong-way” sign to try to get the driver’s attention.
Alerts also are immediately sent to ADOT’s Traffic
Operations Center and the Arizona Department of Public Safety so traffic
operators can quickly activate freeway message boards to warn other drivers
while state troopers can respond faster than relying on 911 calls.
Since it went operational in January, the system has
detected more than 30 wrong-way vehicles entering I-17 off-ramps and frontage
roads. One vehicle was detected on I-17 in north Phoenix on July 5 and the
driver was stopped by AZDPS. The majority of drivers in vehicles detected by
the I-17 system have turned around on exit ramps without entering the freeway.
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