New CDOT Signs Urge Motorists to Merge Later Approaching Work Zones

AASHTO Journal, 26 July 2013

The Colorado Department of Transportation this month announced a plan to use new sign messages with the intent of cutting down on traffic delays through construction zones.

Known as “late merge,” the signs are part of a traffic control program emphasizing the use of open lanes until a work zone’s actual merge point.

“Our engineers have observed congestion increasing through construction projects when vehicles merge into a single lane too soon, creating unnecessary backups prior to the work area,” said CDOT Director of Operations Ryan Rice in a statement. “Our goal is to improve both traffic flow and work zone safety by reducing the frustration and confusion that drivers often experience when merging. By following the directions on the signs, drivers should experience reduced delays.”

Two CDOT projects have put the late merge signs into service. Drivers entering either work zone are directed in the following order:


A video demonstrating late merge is posted on YouTube on the “CDOT Media” channel.

According to CDOT, the late merge strategy has proven effective in congested work zones by improving traffic flow and reducing delays as drivers alternate merging into the open lane. Drivers are advised to still merge early when driving through work zones during non-congested periods.

“We’ve seen drivers merge too early, probably in fear that other drivers won’t let them into the traffic queue down the road,” said Rice. “We appreciate motorists wanting to change lanes early so they can avoid the potential difficulties in merging, but drivers should use both lanes all the way up to the designated merge point when the highway is congested.”

Study data have shown that when used properly, the late merge method can shorten queue lengths by as much as 35 percent.

CDOT will be evaluating the effectiveness of the late merge signage to see how well it improves traffic flow. If it reduces congestion and queue times, future projects could implement the signing elsewhere in Colorado.

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