Colorado sets the pace for winter traffic

By using police vehicles as “pace cars,” CDOT hopes to improve traffic flow during ski season

Transportation Management News November 01, 2011
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The Colorado Department of Transportation (CDOT) has struggled with how to deal with Sunday ski-season traffic on eastbound I-70 in the mountain corridor for years, according to Its new plan of action is to use police cars to set the pace to improve traffic flow.
This type of traffic management is referred to as pace-car speed harmonization. CDOT experimented with pace-cars on a Saturday in August and a Sunday last month, and officials have decided to test it out on winter Sundays.
The technique calls for police cars with flashing lights to travel along the I-70 mountain corridor at a set speed, with the aim of getting vehicles behind them to match the speed, avoid tailgating and eliminate accidents.
CDOT used the technique on Sunday, Sept. 25, from 11:15 a.m. to 3:15 p.m., for the 27-mile stretch of eastbound I-70 from Silverthorne to Empire Junction. The agency said speeds for the police-led platoons of cars and SUVs averaged 55 mph from Silverthorne to the Eisenhower/Johnson Memorial Tunnels, 50 mph in the tunnel and 60 mph from the tunnel to Empire Junction.
"When traffic congestion occurs, the average speed along this 27-mile segment varies between 10 and 30 mph," CDOT said in a statement that announced the planned January launch of the technique.
"The data showed very high compliance among drivers, and speed differentials between vehicles were reduced, even for vehicles traveling outside the paced group of vehicles," the agency added.
Typically, a police car enters the traffic flow every 10 minutes or so, said CDOT spokeswoman Stacey Stegman.
In last month's Sunday test, hourly vehicle counts varied between 1,879 and 2,273, putting them generally within the "peak capacity" measures for the corridor, Stegman said.
During the hours pace cars led traffic on I-70 last month, CDOT was able to see improvement in the traffic flow east of the test area, from Empire Junction to the Twin Tunnels near Idaho Springs, Stegman added.
"By pacing these groups of vehicles, it allowed the funnel to drain" more efficiently, Stegman said of the reduced congestion east of Empire Junction.
CDOT regional director Tony DeVito said that during September's test, the backup at the Twin Tunnels was only about 1,000 feet, compared with a backup that typically stretches four times that length at a comparable time when speed harmonization is not being used.
Stegman said CDOT believes speed harmonization might be even more effective during winter-driving conditions because at those times, there often is a greater "speed differential" among motorists.

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