Vail by Seth W. Chalmers, P.E.  Pima County Department of Transportation

36 Colossal Cave Road Realignment and Roundabouts Layout

The Pima County Department of Transportation (PCDOT) is proposing improvements at nine intersections as part of a federally funded project to improve safety.  PCDOT is conducting a public outreach effort in advance of the project to obtain public input and to provide informational/educational outreach on roundabouts as a safety improvement.  A series of five public meetings were held at various locations throughout Pima County in April, and the presentations as well as a survey are posted on the Pima County website. Once all the public input from the meetings and the website is received, recommendations will be made to County Administration concerning further development of the project.


PCDOT’s public outreach effort included a public meeting held at Acacia Elementary School on Tuesday, April 19 from 6:00 to 7:30 pm; approximately 50 people attended. At the meeting, representatives from PCDOT presented a proposal for single-lane roundabouts at two Vail intersections: Colossal Cave Road at Via Ranch Del Lago and Colossal Cave Road at Camino Loma Alta.  The project proposal also includes the realignment of Colossal Cave Road with Camino Loma Alta.


The proposed roundabout at Colossal Cave Road and Via Rancho Del Lago would increase safety and reduce congestion by providing a safe, efficient, and continuous flow of traffic for all three legs of this intersection.  Because the heaviest traffic comes from subdivisions along Camino Loma Alta, it makes sense to realign Colossal Cave Road with Camino Loma Alta to accommodate both existing traffic and traffic growth in the future.  A roundabout located on the proposed realignment would provide safe and efficient connectivity to traffic on Colossal Cave Road east of the project.


The old proverb, “An ounce of prevention is worth a pound of cure,” perfectly expresses why PCDOT is proposing more roundabouts for traffic control at intersections. As Pima County continues to grow so will traffic, and the potential for congestion and fatal and serious-injury crashes will increase. Roundabouts last longer and move low and high volumes of traffic more efficiently than all-way stops and traffic signals.  Additionally, roundabouts cost less to maintain than traffic signals. Roundabouts are also much safer than standard (i.e., stop-controlled or signalized) intersections. According to a study by the Federal Highway Administration (FHWA) and the Insurance Institute for Highway Safety (IIHS), roundabouts reduce injury collisions by 75% and fatal collisions by 90% compared to standard intersections.  This reduction is due to two major characteristics of roundabouts. First, roundabouts have lower operating speeds (typically between 15 and 23 mph) than traditional intersections.  Second, roundabouts reduce the number of vehicular conflict points at an intersection from 32 to eight, completely eliminating all conflicts that lead to the most dangerous kinds of crashes—T-bone crashes. The FHWA and IIHS study also showed that roundabouts reduce vehicular collisions with pedestrians by 40% because of the lower speeds, significantly shorter crosswalk length, and refuge islands on each approach that allow pedestrians to cross one lane and one direction of traffic at a time.

About author View all posts

Guest Author