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Castle Rock details two‑decade roundabout program; town reports fewer injury crashes and lower life‑cycle costs
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Summary
Town of Castle Rock transportation staff described a long‑running program of roundabout construction that now includes about 30 roundabouts, a 2012 design criterion requiring roundabout consideration for collector intersections and reported safety and operational gains, including fewer injury crashes and lower long‑term costs versus signals.
Jacob Vargas and Tom Reif of the Town of Castle Rock outlined the town’s multi‑year roundabout program, describing design standards, development incentives, crash reductions, and life‑cycle cost considerations.
Jacob Vargas (Town of Castle Rock transportation staff) called the roundabout “the poster child of a safe system approach,” saying roundabouts reduce severe conflict points, slow vehicles to survivable speeds and reduce broadside and approach‑turn crashes. He described a 20‑year program that began with residential installations and expanded to arterials, interchange roundabouts and downtown mini‑roundabouts that preserve parking and accommodate fire apparatus with mountable truck aprons.
Town staff said Castle Rock now has about 30 roundabouts across residential collectors, arterials and a recent interchange area; a major new development (Dawson Trails) has 13 planned roundabouts in its site plan. The town revised its transportation design criteria in 2012 to require that collector‑to‑collector intersections and above consider roundabouts before signalization.
Castle Rock presented before‑and‑after safety and operations data for specific intersections. One arterial conversion that previously carried a signal reported a level of service improvement from C–D to A–B after conversion and a 20% reduction in total crashes with elimination of broadside approach‑turn crash types. The downtown mini roundabout, built to retain nearby parking and allow fire‑truck movements via a mountable center, removed side‑street stop delay and performed well in winter conditions according to staff.
On costs and maintenance, town staff framed the comparison as life‑cycle costs. They provided a planning example with an estimated $2.2 million lifecycle cost for signal operation and maintenance over a multi‑decade horizon versus an approximate $2.0 million one‑time roundabout construction cost (the town noted the signal figure included ongoing retiming and maintenance). Staff said the roundabout option also yields fuel and emissions savings and reduces delays.
Design lessons included avoiding grades exceeding 4 percent (which complicate drainage and biker/motorcycle safety), using concrete pavement in high‑truck areas and durable thermoplastic markings in lieu of paint or tape. Staff also described staged build‑out: designing for future multi‑lane operation but initially striping fewer circulating lanes, then adding lanes later, sometimes via re‑striping to address angle and side‑swipe crash risk.
Jacob and Tom said public outreach and education were central to acceptance; the town provides informational materials and videos at project open houses and online. Castle Rock noted there remain locations where roundabouts were not feasible because of right‑of‑way or drainage constraints, and on rare occasions the town has implemented a signal instead.
Funding for many roundabouts comes from development impact fees; the town’s 10‑year capital improvement program schedules an average of one roundabout every three years. Staff offered to share design dimensions and performance data on request.
"Well‑designed roundabouts save lives," Jacob said, urging practitioners to consult the updated 2023 roundabout design guidance and to account for local constraints when planning.
