Study Zipper lane on I-70 would trim eastbound travel time

Date: Aug. 27th, 2010
Contact: Jeffrey Leib Denver Post

Adding a reversible “zipper” lane to eastbound Interstate 70 in the mountains would cut peak-hour Sunday evening commutes in the winter from 91 minutes to 46 minutes between Silver Plume and the El Rancho exit, according to initial results of a state study.

But travel in the single remaining westbound lane during the same window would jump from 35 minutes to 79 minutes, the Colorado Department of Transportation study found.

CDOT has spent about $170,000 looking at the feasibility of adding movable barriers to the 15-mile stretch of I-70 between a point just east of Georgetown and the base of Floyd Hill.

State Rep. Christine Scanlan said she was disappointed with some results of the study, but she hopes the preliminary results lead to practical solutions. Perhaps a segment of 5 or 10 miles — rather than the entire 15 mile stretch — could be more workable and affordable, she said.

While the moveable barrier would be in place for about 15 miles, travel-time results were measured for a full 25-mile distance that included five miles added to each end of the barrier-separated section of the highway.

That's because putting a reversible-lane system in place will impact traffic flows for some distance on each end of the barrier-separated lanes, said Tony DeVito, CDOT's regional director who has responsibility for this section of I-70.

The study looked at the possibility of installing the reversible lane on I-70 during busy summer travel periods, but found that only on winter Sundays is there enough of a directional imbalance between eastbound and westbound traffic to justify taking a lane heading one direction and reversing it to create three lanes.

On Sundays in winter, the peak-hour traffic volume for the 25-mile stretch between the Silver Plume and El Rancho exits is 3,161 vehicles an hour eastbound and 1,893 vehicles westbound, according to the study.

Legislative direction
This year's session of the Colorado legislature passed a law urging state transportation officials to strongly consider the zipper-lane option as a short-term method for relieving congestion in the mountain I-70 corridor.

State Sen. Dan Gibbs said the initial results were similar to what he expected, and he “thought it was pretty fascinating.”

“I've really thought the zipper lane proposal was a way to look outside the box, to look at short-term solutions to improve transportation flows,” he said. “For the first round of analysis, I'm pleased with it.”

Barrier Systems Inc., of Vacaville, Calif., makes the mobile barriers, which would be staged in the shoulder of westbound I-70's left lane and, when deployed, moved in a continuous operation by a special vehicle to a position that temporarily and safely separates the two westbound lanes.

Barrier Systems estimates it would take about 1-1/2 hours for its machines to move barrier over the 15-mile stretch to create the extra eastbound lane, DeVito said.

While CDOT's initial study shows I-70's geometry may allow installation of barriers to create the additional eastbound lane, the agency must conduct a far more detailed analysis over the remainder of the year to determine whether the project is fully feasible and cost-effective, DeVito said.

One concern is how the zipper lane would work when installed in the westbound bore of the Twin Tunnels near Idaho Springs.

CDOT estimates it would cost about $35 million to install the temporary barrier system and it would be used about 17 Sundays a year. The agency has not yet identified a source of money.

Snow issues
A second phase of the study will look at snow removal and emergency-response and incident-management procedures that would be needed to maintain a free flow of traffic in the reversed lane, DeVito said. For instance, there is no place to push or plow snow from the zipper lane, he said.

Once cars or trucks enter it, they are in a closed, express lane with no other entrances or exits for its full 15-mile length, he added, and that could make it difficult to extract vehicles involved in accidents or stalled with mechanical problems.

DeVito said the second phase of the study also will look at the potential for tolling traffic using the reversible lane for the eastbound flow.

Acknowledging the study's finding on the potential delay of westbound traffic, State Sen. Chris Romer said the reversible-lane concept remains a “short-term solution for Sunday evenings,” especially if truckers can be enticed to avoid the highway during hours the zipper lane would be in place.

Some officials have discussed offering incentives to truck operators to do so.

CDOT's study found that adding the reversible lane would have a negligible effect on both average and peak-hour travel times for traffic using the three eastbound lanes during zipper-lane operation, whether trucks remained in the traffic flow or not.

But for the single westbound lane in the 1 p.m. to 9 p.m. window on winter Sundays, it would take about 10 minutes off both the peak and average travel time if trucks were removed from the flow, according to the CDOT analysis.

The agency hopes to complete the second phase of its reversible-lane study by December and make a “go or no-go” decision on whether to proceed with the plan at that time, agency executive director Russell George told the state's High Performance Transportation Enterprise board of directors last week CDOT separately has produced a draft environmental impact statement for the I-70 mountain corridor that is pushing select highway improvements and an advanced guideway train or monorail system as the long-term solution for congestion in the corridor. However, such solutions would cost billions of dollars and funding sources have not yet been identified for them.