DENVER -- Adding an extra, temporary eastbound lane to Interstate 70 would cut travel time from ski resorts to Denver by about half.

That's according to the initial results of a study commissioned by the Colorado Department of Transportation. It found using a reversible "zipper" lane on winter Sundays would cut the drive time from Silver Plume to El Rancho from 91 minutes to 46 minutes, CDOT said.

The extra lane would be borrowed from westbound I-70. However, the study found that the drive into the mountains would grow from 35 minutes to 79 minutes as a result.

And if a reversible lane were to be implemented on I-70, it would be used only for eastbound traffic during the ski season on Sundays.

"The study determined that westbound traffic is too heavy to implement a reversible lane in the eastbound direction in the summer. It also found that adding a reversible lane in the westbound direction would provide little benefit," CDOT said.

"Even though westbound traffic is heavy on Friday afternoons and Saturday mornings, the highway is not at capacity for enough time to open the lane, which can take up to 1.5 hours to change direction. Therefore, if a reversible lane were to be implemented on I-70, it would be used only for eastbound traffic during the ski season on Sundays," according to the study.

Colorado lawmakers passed a bill this year urging CDOT to consider using a zipper lane to ease weekend backups on I-70.

The "zipper lane" can reverse direction during peak travel times, and the proposed lane would begin on eastbound I-70 west of Empire Junction and continue to the base of Floyd Hill, a total project length of about 15 miles, CDOT said.

The study, conducted by the University of Arizona and the University of Colorado at Denver, also found the zipper lane "geometrically feasible."

The primary purpose of the study was to assess what the effects to westbound traffic would be if the highway was reduced to just one lane in this direction. It analyzed and simulated traffic operations based on collected traffic data for 236 Sundays between January 2004 and March 2010. However, it did not take into consideration, bad weather or accidents.

CDOT will now conduct the second phase of the study, looking at issues like snow removal, emergency response, wildlife, modes of operations and other environmental issues and concerns about access to local communities.

The second phase is expected to be completed in early 2011. Phase II of the study will ultimately provide answers as to whether this system can safely and effectively move forward.

"If it is found to be safe, affordable and feasible, the system could be implemented in the 2011/2012 ski season," CDOT said.

It's not clear yet how the zipper lane would be funded. The system is estimated to cost between $30 and $35 million.

"While reversible lanes have been used with success in several states, they have not been used under the challenging conditions presented on the I-70 west mountain corridor," said Tony DeVito, CDOT Region 1 Director. "We know of no cases where zipper lanes have been used for such a long stretch of highway with no access in or out on a corridor with extreme weather and leaving only one lane on an Interstate highway. We are encouraged about the prospect of this project but we are proceeding cautiously to assure it provides a safe short-term solution to traffic without causing unacceptable problems for those traveling in the opposite direction or for the local communities."

The entire study can be found at http://www.coloradodot.info/projects/I70reversiblelane.