I-70 pace cars experiment is working, CDOT says -- just not all the time

The Associated Press is reporting that the Interstate 70 pace car program was suspended Sunday in lieu of a review by the Colorado Department of Transportation. But while that's true in a technical sense, it's also a bit misleading. The CDOT program has only been officially shelved for this next weekend, and spokeswoman Stacy Stegman says that up until now, it's been helping reduce travel times incrementally, if not dramatically.

Thanks to the pace cars, Stegman says, the travel time between the Eisenhower Tunnel and the entrance to C-470 during heavy travel times has been reduced by an hour from last year to this year, factoring in similar dates, weather conditions and volume. But she admits that this improvement hasn't sunk in to most commuters, in part because many folks still can't comprehend how the pace car concept works.

"One of the things we're hearing from people who are writing in is that they're seeing open road in front of the pace car," whose drivers are instructed to maintain a steady rate below the speed limit in order to even out the flow of traffic. "They think they should be able to go 65, and we're making them go 45, so they feel like they're being slowed down. But we've been seeing huge success at the twin tunnels near Idaho Springs -- free-flowing traffic. So we know there's a benefit."

Not a consistent one, though. In Stegman's words, "Things are failing quicker on the west side of the tunnel, and we're trying to figure out why" in order to reduce the technique known as "metering" -- stopping traffic until vehicles stacked up inside the tunnel are cleared. "People think we're metering to pace the traffic, and we're not. It's not something we want to do, but something we have to do, so that we can make sure there's access for emergency vehicles."

Such confusion is understandable. "The pacing concept is counter-intuitive -- the idea that you need to go slower to go faster," she concedes. "But it's like your faucet. When you turn on the water full blast, water builds up in the sink. But when you turn it on at a good, medium level, it continuously drains. And using the pace cars is the same idea."

The traffic-free road to the Eisenhower Tunnel earlier today.
The traffic-free road to the Eisenhower Tunnel earlier today.

Over time, however, CDOT staffers have seen that "when traffic becomes too heavy, it paces itself by slowing down," Stegman notes. "You can't pace it anymore, because it's slower than you need to pace. So we're looking for the optimal level of when to pace. When traffic's too light, we're slowing people too much, and when it's heavy, the traffic slows by itself, and there isn't enough of a gap to keep pacing."

This last revelation has become clear in recent weeks. "We hoped that it would help even when the traffic was heavy," she allows. "But so much of it has to do with driver behavior -- how they're driving, how they're bunching, how they're jockeying for position. Ideally when we're pacing, you have to slow down and get comfortable -- relax and leave room. But when traffic gets heavy, everybody gets a little anxious as they're trying to get home. They bunch up, change lanes frequently, and that's when we see this conflict."

Witness Sunday, when 43,953 vehicles passed through the tunnel, as compared to 42,590 on the same Sunday in 2011. Despite an increase of more than a thousand autos, the commute time was no worse, but neither was it better, and CDOT personnel could see that the pace cars weren't helping. Hence, Stegman says, CDOT will be monitoring traffic levels this next weekend, as well as those that follow, "to see if things will exceed our comfort level for running this operation.

"We're trying to get a better handle on this," she adds. "After all, this is an experiment. We never said it was going to solve all the problems. It's not a magic bullet -- it's just something we can do as a temporary measure, and we hope it will make a difference."

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