SUPERIOR — Commuters between Superior and Louisville could one day be crossing the McCaslin Boulevard bridge over U.S. 36 British style — on the wrong side of the road — if a novel type of interchange design is adopted to ease traffic congestion there.
The “diverging diamond” interchange, in which motorists criss-cross for the length of the bridge to the opposite side of the road so that all turns are unobstructed, is one of three options that transportation planners presented at a public meeting in Superior on Thursday night.
The other two options were building a large rotary on the north side of the bridge or installing a second left-turn lane on McCaslin for cars getting onto westbound U.S. 36.
The diverging diamond interchange is new in the United States, with only a handful of them in existence across the country. The first one opened to traffic in Springfield, Mo., less than three years ago.
“It’s counterintuitive,” said Troy Russ, Louisville’s planning director and the project manager for the interchange improvements. “But if you eliminate protected (green arrow) left-hand turns, you get 15 percent to 30 percent additional capacity with no significant additional cost.”
Traffic on northbound McCaslin regularly bunches up at the left-turn light where Boulder-bound commuters get on westbound U.S. 36. Traffic counts show anywhere from an average of 31,300 to 41,100 vehicles a day on McCaslin on either side of the bridge.
One critical advantage of changing the current interchange into a diverging diamond, Russ said, is that it wouldn’t require the McCaslin bridge over U.S. 36 to be replaced.
Both municipalities teamed up to fund the $80,000 interchange study, and transportation planners hope to incorporate the project into the larger U.S. 36 improvements that are being carried out by the Colorado Department of Transportation and the Regional Transportation District over the next several years.
No price tag and no specific timeline have been identified for completing the interchange improvements.
Dick Marin, a Superior resident for nine years, said he was intrigued by the diverging diamond design presented Thursday. But he also wondered whether motorists would catch on to opposite-side driving.
“How many accidents is that going to cause before people learn how to drive it?” he said.
