Crashes, delays drop at Vandehei Interchange

June 18, 2012

The number of crashes and the average wait times for vehicles both dropped during the first year the roundabouts at the Vandehei Interchange on I-25 in Cheyenne were open to traffic.

The roundabouts opened on May 25, 2011, 25 days ahead of schedule. Reiman Corp. of Cheyenne completed the project for $6.1 million.

In the year since the roundabouts opened there have been three crashes reported at the interchange. None of those crashes resulted in injuries.

During the year prior to beginning the construction that widened the Vandehei bridge and replaced the intersections on each side with roundabouts, there were 11 crashes and four people injured at the interchange. When compared to the average number of crashes annually during the five years prior to construction, crashes dropped 54.5 percent during the first year the roundabouts were in operation.

Traffic engineers consider three years of crash data the minimum needed to draw long-term conclusions about the performance of an intersection, but the data from the roundabouts’ first year of operation are considered a good start to the ongoing assessment.

Studies completed before the project was designed indicated under projected traffic volumes the existing intersections with stop signs would result in average side-street delays of 37 to 45 seconds per vehicle during peak traffic. If traffic signals were installed, the projected average delay per vehicle during peak volumes was 32 seconds.

“We had predicted an average delay of somewhere in the six to eight seconds per vehicle range for roundabouts, and we’re doing better than that,” said Paul Jones, WYDOT’s assistant state traffic engineer. “So these things are operating quite well and quite safely. We’re not getting long queues of vehicles waiting to enter, and the queues dissipate quickly.”

However, improvements can still be made, Jones said. During heavy snowstorms, the lack of storage space for snow creates difficulties in clearing the roundabouts using conventional snow-removal equipment. Also, some drivers still are not clear on the rules for driving through the roundabouts.

Drivers approaching a roundabout need to yield to any pedestrians at the crosswalk and then look to the left and yield to traffic already on the roundabout. If there is no traffic approaching from the left, drivers do not have to stop before entering the roundabout.

Vehicles entering the roundabouts from the bridge do not have the right of way. They must yield to traffic already on the roundabout, just like vehicles entering from the exit ramps or service roads.

Once on the roundabout, drivers should proceed to their exit and use their right-turn signal to let other drivers know they’ll be leaving the roundabout at the next street.

Videos, animations and graphics on how traffic flows on a roundabout are available on WYDOT's roundabout education page.

There are currently four roundabouts on Wyoming’s highway system, and a fifth is scheduled for completion later this year at Hoback Junction.

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