Longmont staff, consultant outline three alternatives — including a Dutch-style roundabout — for 21st and Main

City of Longmont staff and an outside consultant presented concept designs on Dec. 9 for the 21st Avenue and Main Street intersection, laying out short-term operational fixes and three geometric alternatives intended to reduce vehicle turning speeds and improve safety for pedestrians and cyclists.

Aaron Provo, senior civil engineer in Longmont's Public Works Department, said the project is in the concept design phase through March 2025 and that construction would depend on funding; staff hope to begin construction in 2027. Provo said the project stems from the Main Street Quarter plan and a public survey that drew nearly 700 responses identifying speeding, long signal waits and poor visibility of people walking and biking as the main concerns.

Chris Vogelsang, a consultant with OV Consulting, described three families of alternatives: focused spot improvements (lower cost, striping and raised tables), compact intersection options with tightened curb radii and raised medians, and protected/"compact" intersection treatments that create distinct space for pedestrians and bicycles. He also presented a Dutch-style, two-lane protected roundabout variant configured to reduce turning speeds and deviate bicycle and pedestrian crossings away from vehicle flows.

"The roundabout has strong vehicular safety benefits because of its geometry," Vogelsang said, adding that the design team reduced the design speed for the circle to about 20 mph to limit circulating speeds. At the same time, he warned the board that roundabout operations would change how traffic platoons through the 287 corridor and that right-of-way acquisition for a roundabout could take several years and be costly because of federal and state requirements on the highway corridor.

Board members pressed the team on several trade-offs. Vice Chair McKay Burrows asked whether a roundabout would require signalization for pedestrians; Vogelsang said pedestrian hybrid beacons or other active devices would be needed to give pedestrians the right-of-way at the set-back crosswalks. Board member Wicklund and others sought assurances that larger bikes and trailers could navigate tighter radii; Vogelsang said turning templates and design-vehicle checks (school bus, delivery truck, fire apparatus) would be run in subsequent design steps.

Several members raised the question of mixing bicycle and pedestrian traffic behind curbs at protected intersections (option 2c). Board member McKee Burrows said she was concerned about ebikes and cargo bikes moving at higher speeds in the shared space. Vogelsang acknowledged the concern and described possible vertical separations or small curbs between modes as design options.

Staff and consultants said they have collected recent counts for pedestrians, bicycles and vehicles and have reviewed crash data and planning documents, including Vision 0 and the BRT study. Jim (city staff) said CDOT had funding for corridor work on 287 and that some decisions will require coordination with CDOT because 287 is a state corridor.

The city scheduled a public meeting on Wednesday, Jan. 29, 5–7 p.m. at the Moose Lodge on 21st just west of Maine to present the study and gather public input, Vogelsang said. The team asked the board to provide refinements and flagged that final design and construction funding would follow selection of a preferred alternative.

The presentation identified trade-offs in cost, right-of-way acquisition time, pedestrian comfort, bicyclist accommodation and operational effects on coordinated signals on 287. Board members generally favored compact or protected intersection options for pedestrian comfort but were split on the roundabout because of corridor operations and land acquisition complexity. The project remains in the concept stage and will return to the board as designs are refined.