By: Kristie Di Cocco, PE, Senior Engineering Associate, Alta
At their worst, roundabouts fail to safely address the presence of bicyclists. At their best, they are a great way to calm traffic and reduce greenhouse gas emissions while providing dedicated space and safe crossings for people walking and biking.
Roundabouts are a critical tool in the traffic management toolbox as they provide both efficiency and improved safety, but they aren’t the right fit for all locations. Engineers see the biggest benefit of roundabouts in their ability to maintain vehicle flow while reducing vehicle delay. From a safety perspective, roundabouts reduce pedestrian crashes by 27 percent and vehicle crashes by 48 percent when compared with signalized intersections. In fact, crashes aren’t just reduced in number but also in severity, as roundabouts have a 78 percent reduction in injury crashes over signals.
At Alta, we are working towards a future where roundabouts not only enjoy the above benefits, but also provide for the safe and efficient movement by people riding bicycles and other mobility devices. Through innovative solutions that mimic protected intersection treatments, people walking and biking can be separated from the main circulatory flow of traffic. This dedicated space provides comfort, but also improves visibility. Roundabouts can also serve as gateway opportunities to visually notify people driving that the character of the roadway is changing and they are now entering a different driving environment.
For example, Alta is providing active transportation design in Anacortes, Washington with the most vulnerable road users in mind. In doing so, we are able to provide a true multi-modal solution that addresses climate change, promotes walking and bicycling and addresses traffic issues all in one round solution.
There are many examples of successful roundabout projects in communities across North America. Here are some Alta is excited to share.
Anacortes, WA Commercial Avenue Complete Street
As part of the Commercial Avenue Complete Street Plan that Alta helped the city develop in 2016, we are working with Transportation Solutions, Inc. to design a roundabout for the City of Anacortes, WA. The 2016 vision established a new multimodal framework for the Commercial Avenue corridor that transforms the WSDOT roadway into a space that is also comfortable and safe for people to walk and bike.
The first phase of design is focused at the most prominent intersection along the corridor that is both a gateway into the downtown core and a junction to the Anacortes Ferry Terminal, a popular destination point. The project plans to reconfigure the intersection from a signalized intersection into a roundabout. Through this process there have been a number of important technical discussions around a design within a constrained space that is able to accommodate higher traffic volumes while also ensuring that the primary intent of the project — making travel easier for people biking and walking — isn’t compromised despite those space constraints.
The project team is in the early stages of evaluating the inclusion of fully separated facilities within the single lane roundabout through a dedicated 6-foot one-way cycletrack for bicyclists and 10-foot sidewalk for pedestrians. This is in contrast to many traditional design approaches that will either force bicyclists into the lane, onto the sidewalk while walking, or include a bi-directional shared use path. Rectangular Rapid-Flashing Beacons will enhance crossings at each leg of the roundabout and both crosswalks and crossbikes are included at each crossing to continue separation.
This high-profile project has the opportunity to help create a paradigm shift for state highways in Washington State and serve as an example for other communities on how to transform their own state highways into multimodal corridors.
Palo Alto, CA Bike Boulevards
Alta worked with the City of Palo Alto, CA to plan and design safety improvements along nine bicycle boulevard corridors throughout the city. After the initial phase was completed, the City selected Alta to prepare design construction documents for four of the corridors. These projects include urban roundabouts, among other traffic calming elements aimed at enhancing the bicycling experience along the project corridors.
The final design of these four corridors included 11 compact roundabouts, which are similar in size to mini-roundabouts, but include more traditional roundabout elements such as landscaped center islands. Due to the restricted size, some larger vehicle turning movements were prohibited. A critical aspect of the corridor design was to maintain the comfort of bicycling along the corridors and through each intersection. To achieve this, Alta paired the roundabouts with other traffic calming elements such as speed humps, chicanes, and raised intersections. The effective use of the compact roundabouts as intersection treatments coupled with the traffic calming corridor elements reduced vehicle speeds and offered bicyclists the opportunity to maintain their physical presence on these low-stress streets leading up to and after the roundabouts.
San Diego, CA Pershing Bikeway
San Diego is nearing completion of one of its most visionary projects, and Alta has been there every step of the way since 2015. The project is in the process of bidding for a 2.6-mile separated bikeway along Pershing Drive through historic Balboa Park. This project is part of the $200 million Regional Bikeway Early Action Program for the San Diego Association of Governments. The bikeway design will provide a crucial commuter connection between the North Park neighborhood and downtown San Diego. Alta led community engagement, concept alternative development, preferred concept adoption, visual renderings, the engineering plan set, preliminary environmental review and agency coordination.
The project includes an urban compact roundabout with an adjacent neighborhood traffic circle, as shown in the plan image above. Caltrans defines a compact urban roundabout as a single lane roundabout in an urban setting with an inscribed circle diameter of 115 feet or less, and exit radii of 39 feet or less. This compact design allows for the safety and flow benefits of a traditional roundabout to be experienced with reduced vehicular travel speeds and a smaller spatial impact on the surrounding landscape. The project also features a large single lane modern roundabout with several key challenges. The project is located on the side of a hill with challenging grades; it also features three legs that create geometry that make it more difficult to control entry and exit speeds. Alta’s design evolved to modify the approach of Pershing Drive to act more like a right angled (square) intersection. Along with the roundabout, Rectangular Rapid Flashing Beacons (RRFBs) will be implemented at each leg of the roundabout, which will increase the visibility of pedestrians and bicyclists crossing the vehicular travelway. All in all, the design will take an intersection that has traditionally been difficult to navigate and transform it into a space that will be safer for all roadway users. After so many years of hard work by so many champions, we are excited to see this project under construction!
How have you seen multi-modal roundabouts in your community? Where would you like to see more? Learn more about Alta’s Engineering practice, and contact Kristie Di Cocco if you’d like to see more roundabouts in your community.
