CO 83 Roundabout at County Line/Palmer Divide Rd. - Preliminary Design

Project completed

About the Project

Preliminary design has been completed. The project is on hold until additional funding is identified and future improvements are determined for this intersection.

The southeastern region of the Colorado Department of Transportation (CDOT) (Region 2) has identified a need to evaluate traffic operations and design of a roundabout at the intersection of CO 83 and County Line/Palmer Divide Avenue located at the boundary of Douglas County and El Paso County. See the Project Map below for the specific location. A project team consisting of representatives from CDOT Regions 1 (serves Douglas County)  and 2, Douglas and El Paso Counties, FHWA, and a consultant design team was formed to advance the design of a roundabout at this intersection and better understand the functional characteristics, associated impacts and costs for future implementation. Characteristics of a properly designed roundabout include elements that provide optimal safety and operations specifically for high speed conditions approaching the roundabout. Design elements may include geometric approaches to slow traffic, advanced signing, pavement markings and raised channelization. With proper design, drivers adjust their speed to navigate the roundabout safely.

For more information, visit the FHWA brochure on Roundabouts and Rural Highways by contacting the project team.

  • A temporary traffic signal was installed to address increased traffic demand at the CO 83 and Palmer Divide Avenue intersection during construction of the I-25 South Gap Monument to Castle Rock project, with the intention of replacing the signal with a roundabout. A traffic signal is not currently warranted at CO 83 and Palmer Divide Avenue and is not anticipated to meet warrants in the coming years. Traffic signal warrants establish minimum criteria for evaluating the need for a traffic signal at a specific intersection. Implementing a signal at unwarranted locations is shown to have negative impacts on traffic flow, including increased crashes, delay, and traffic violations. With that in mind, CDOT Region 2 evaluated and selected a roundabout to address traffic operational and safety concerns, including conflicts created by high-speed conditions, now and into the future. Roundabouts are a safer type of intersection as they reduce fatal and injury crashes by 78% (FHWA). They are also efficient in terms of keeping people moving. Even while calming traffic, they can reduce delay and queuing when compared to other intersection alternatives. For more information about roundabouts, there are video and case study links provided on this project website page.
  • The project team has completed the necessary data collection and traffic operational analysis that confirmed a roundabout will operate acceptably at CO 83 and Palmer Divide Avenue based on current and future projected traffic volumes through 2045. Based on the lane recommendations from the traffic analysis, the project team developed a preliminary design of the roundabout to better understand the impacts and construction cost. See the Project Schedule below for more information on upcoming activities and timelines. CDOT and the local agencies are currently reviewing options to obtain project funding for final design and future implementation. The project does not currently have full construction funding.

Coordination of Other Projects In the Area

Roundabout and Case Studies

Frequently Asked Questions (FAQs)

Q: Why is a roundabout being proposed instead of just keeping the existing traffic signal?

The current traffic signal was installed as a temporary span wire signal to address increased traffic along CO 83 during the construction of the I-25 South GAP Monument to Castle Rock project, with the intention of removing it after construction. With the completion of the I-25 GAP project, the intersection no longer meets the required warrants for a traffic signal.

Additionally, as provided on the project website, recently collected crash data shows that crashes have continued to occur at the intersection after the traffic signal was installed. An analysis of the crash data indicates there is a moderate to high potential for crash reduction with improvements at the intersection. The roundabout is being proposed as a proven safety measure that will also provide improved traffic operations that could otherwise not be accomplished at this intersection.

How will the roundabout work with the traffic volumes and high speed along CO83?

The project team evaluated future traffic volumes projected at the intersection and found that by the year 2045 the roundabout will operate with significantly less delay than a traffic signal. During peak traffic hours, vehicles entering from County Line Road will enter the roundabout with gaps that are created by turning vehicles exiting the roundabout (see the project website for a video illustrating how only a small gap in traffic creates enough space for a vehicle to enter a roundabout). The traffic analysis shows there will be less delay for drivers on County Line Road when compared to a traffic signal. And during low volume hours, drivers will be able to immediately enter the roundabout and turn onto CO 83 without having to wait for a green light.

The project team is giving particular emphasis to the visibility of roundabout with the proposed design. Key features such as warning signs, raised medians on the approaches, a raised central island, and lighting are all being included to provide advance notice for drivers to recognize the roundabout with ample time to decelerate to the roundabout safe speed of approximately 20 mph.

When was traffic data collected? Does it reflect current conditions given COVID and the I-25 GAP project?
The project team worked through the existing and forecast traffic volumes over several iterations and sources. The project team obtained historic daily traffic volumes from CDOT’s database and obtained intersection traffic counts in October of 2021 to validate the data. Future traffic volumes were projected to grow at 3% per year, which is representative of the surrounding area.
How will large trucks and trailers drive the roundabout?
Accommodation of trucks and combination vehicles is being addressed by proposing an appropriately sized circle and including a low raised area at the center of the roundabout, called a truck apron. Vehicles with a wide turning radius may drive over the truck apron. Please see the project website for a video of a large truck navigating a roundabout. The turning paths of trucks and trailers will be smoother than the current condition and less prone to load shifting because curves are longer and have flatter radii.  It is understood that making through movements using the roundabout will introduce curvature to all vehicle paths, but this is intended to slow all traffic that cross paths and reduce the potential of high speed crashes.

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CDOT is committed to producing the best roundabout design possible to allow this intersection to operate safely and effectively into the future.