For all of the fanfare and excitement surrounding the notion of an Interstate 70 “zipper lane” to reduce mountain traffic congestion, the Colorado Department of Transportation says the idea most likely won’t be implemented until the fall of 2011. It’s even possible the program may never come to fruition. Numerous studies still have to be completed, along with input from mountain communities along the affected corridor. Those studies would then allow CDOT to create a projected fiscal note.

However, the data from an initial survey already shows that the zipper lane could only feasibly be used eastbound on Sundays in the fall and winter.  Actually placing the barriers on the interstate to create the 3-lanes-versus-1 would take about 90 minutes, and CDOT says it must have a “lull” in the opposite direction of traffic in order to install the barriers.  Otherwise, reducing down to one lane would create major delays and other safety problems for those traveling in that direction. The survey data suggests that neither weekend summertime traffic nor Friday wintertime traffic provide the necessary “gap” in traffic flows to make placement of the zipper lanes feasible at those times. Only the Sunday mass-exit from the mountains provides the necessary time for traffic to realize the maximum benefit.

While the additional lane of eastbound traffic would significantly cut travel times out of the mountains (from an average of 79 minutes down to 40 minutes), an additional burden would be placed on westbound travelers. The study estimates Sunday westbound travelers would see their drive times jump from roughly 34 minutes to anywhere from 60 to 69 minutes, depending on whether or not trucks are allowed to use the single lane at the time.

The idea of installing a zipper lane isn’t new; they are frequently used in construction zones. But the notion of systematically installing 15 miles of zipper lane along a federal interstate would represent a remarkably unique, first-time experiment in the country of manipulating federal roadways in such a manner for the purpose of alleviating congestion in a mountain corridor environment for such a lengthy stretch of highway. For that reason, CDOT spokeswoman Stacey Stegman says the agency is “going cautiously.”

The study released by CDOT is the “Phase I” study which essentially studied traffic patterns to assess overall feasibility.  The Phase II study would have to delve into deeper issues of the zipper lane concept. Stegman added, “Phase II is where we’ll answer the really tough questions about issues related to snow removal, incidents, emergency response, etc.  We need these issues resolved before we can decide if this is something worthy of a major public investment.”

The idea for the zipper lane was proposed and passed in the last legislative session as Senate Bill 184 from State Sen.Chris Romer, who has long sought a creative solution to the I-70 “bottleneck” caused when people travelling into or out of the mountains create rush hour-like backups. Romer’s bill, however, does not compel CDOT to implement the zipper lane.