New stoplight technology helps backburner 8th Street interchange

       A year ago, on the advice of state transportation officials, a project to run Highway 24/Cimarron Street over Eighth Street became a top regional construction priority, right behind the first phases of a new interchange at I-25 and Cimarron, a third of a mile away.

A view from the southbound I-25 off-ramp lane shows its intersecton with Highway 24/Cimarron Street. The future Cimarron/I-25 interchange is slated for a greatly revised off-ramp layout, including the elimination of this stoplight and the overall reduction of driving delays. About 1/3- mile to the west, Eighth Street crosses Cimarron. "Adaptive" technology is planned for the stoplight there.
Westside Pioneer photo

       Now the state sees that Eighth Street interchange as less urgent.
       And it's all because of a little technology.
       An advancement called “adaptive signal timing,” which the city is close to installing at all the crossings along Highway 24 between I-25 and 31st Street, reduces waiting time for cars at intersections.
       “It's backing up there today,” said Dave Watt, a Colorado Department of Transportation (CDOT) engineer, of the Eighth Street intersection. “It [the adaptive system] will improve operations.”
       Choosing his words carefully, Watt noted that the state's Preferred Alternative from the 2004-2012 Highway 24 expansion study still calls for an interchange at Eighth Street, but expressed confidence that an upgraded I-25/Cimarron interchange could function acceptably even if Eighth stayed at grade for the time being. Previously, engineers had feared that improvements in traffic flow at I-25 would be negated by backups at Eighth.
       As always, a key factor is money. The I-25/Cimarron interchange is now estimated to cost $95 million, while its counterpart at Eighth is scoped at $70 million. Neither has construction funds now, although the interstate project received design and right-of-way money last year that would allow work to start there as early as 2014, CDOT officials have said.
       Rob Helt of City Traffic Engineering said he has not talked to Watt about the city's adaptive signal timing plans, but is aware that CDOT wrote a “glowing report” on a recently installed system of that type in Greeley.
       Helt was also cautious about predicting major flow improvements, at least at “very busy intersections” such as Eighth, because both directions tend to have steady traffic most of the time. “Once Cimarron gets over capacity, the problem [of backups] won't go away,” he said. “I don't have a magic tool to do that one.”
       However, he believes there is room for some improvement and that with an adaptive system drivers will be especially satisfied during off-hours. He gave as an example 6 a.m. on a Sunday. Currently, people on a cross street have to wait through the cycle, even if there's little or no highway traffic. But with an adaptive system, the computer will read that traffic gap and give green time to the cross street.
       Making the process more scientific, the system will simultaneously “tell” the stoplights east and west of it so they can adjust their timing as necessary.
       Off-hour highway drivers will also be less likely to hit red lights - as they do now when just a single cross-street motorist pulls up to the intersection. Instead, the adaptive system will seek openings in the highway flow before letting the side street traffic through - but also not let them wait too long, Helt explained.
       Adaptive signal timing is not used anywhere in the Springs now. Highway 24 is one of several arterials being looked at for the digital technology under a “congestion mitigation air quality grant” the city received from the Federal Highway Administration (FHWA), he said.
       Actual installation is a few weeks off. Several companies offer adaptive technology variations, and “we're still evaluating different systems,” Helt said.

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