Spearfish reviews traffic study at Colorado Blvd.

Pioneer photo by Mark Watson

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SPEARFISH — As due diligence in preparation for the 40-acre sports complex being built along with the 180-lot housing development currently under construction near Exit 17, city officials contracted with HDR, Inc. to complete a traffic impact study for the area to see what issues might need to be addressed as the sporting events center attracts more travelers to Spearfish.

The study focused on five intersection points around the development area – the Interstate – 90 on and off ramps at Exit 17; the intersection of Colorado Boulevard and U.S. Hwy. 85; the intersection of St. Onge Road and U.S. Hwy. 85; and the four-way intersection at Colorado Boulevard and Rainbow Road. The study also looked at three entry and exit points to the development area.

Stacia Slowey, traffic engineer with HDR, explained to the city council Monday that the study identified 2022 and 2045 as the target dates at each intersection, and assigned a grade level to each based on those service levels. Both years would see major influxes in traffic flow.

“It’s similar to grade school grading, except a level of service ‘C’ is what we’re targeting,” she said. “It’s a good efficiency of use of your intersections. Anything less than ‘C’ is something that we are wanting to improve upon.”

Slowey projected that two of the intersections would be operating at a service level of ‘F’ by 2022 if no improvements were made.

One of those intersections is the westbound ramp terminal at Exit 17; however, that deterioration won’t be caused by the development, so those improvements will be monitored and made by the South Dakota Department of Transportation (DOT). The other issue was identified at the intersection of Colorado Boulevard and Highway 85, which the study shows, will be impacted by the development.

“The DOT is actually planning intersection improvements at this intersection, but it’s unfortunately not going to happen until after this development gets built,” she explained.

Those improvements are planned to take place in 2023. Mike Harmon, city administrator, recommended that the city move forward to coincide the improvements needed at Colorado, which is the city’s responsibility, with the DOT’s project on Highway 85.

“I think what we need to do is work into our budget for 2022, the design contract for those improvements on Colorado with construction to tie in to 2023 with the DOT projects so we have one project out there,” he said.

In the meantime, as the housing development construction continues and homes begin to be built and moved into, the study recommended temporary improvements to the traffic flow at the intersection by adding a right turn lane.

Slowey outlined what the city would need to add to the Sky Ridge development in order to mitigate traffic flow disruption.

“Basically, by year 2022, we need a westbound left turn lane at each of the three proposed access points and then at the middle one, which is Sky Ridge (Road), we would need an eastbound right turn lane,” she said.

Slowey said that by 2045, based on increased traffic volume projected over time, additional turning lanes will need to be added at Colorado Loop Road.

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