Inman Square Peanutabout

Inman Square "Peanutabout"

The intersection of Hampshire and Cambridge streets at Inman Square in Cambridge, Massachusetts, presents a challenge familiar to many cities: how to safely move pedestrians and bicyclists through a busy, elongated, multi-approach intersection. Due to its low-angle skew, the Inman Square intersection spans more than 250 feet, creating confusion and chaos for anyone passing through it. In the absence of an obvious conventional solution, local advocates Boston Cyclists Union recognized the need to innovate, which led them to KAI's Boston office.

As previous efforts to fit a traditional roundabout into Inman Square failed due to lack of space, the KAI design team identified a solution that used a pair of mini roundabouts connected in the middle. Initial operations assessments using the Highway Capacity Manual (HCM) 2010 and HCM 6th Edition roundabout operations models developed by KAI suggested the design was feasible, so the team proceeded with development. Principles identified in the Federal Highway Administration’s (FHWA) Separated Bike Lane Planning and Design Guide—coauthored by KAI—were used for the bicycle treatments, and the principle-based design approach in NCHRP Report 672: Roundabouts, An Informational Guide, Second Edition, developed by KAI, informed the overall design and helped to assess the tradeoffs necessary in the constrained urban environment. The resulting peanut-shaped design led the Boston Cyclists Union to coin the term “peanutabout” when describing it.

The peanutabout’s traffic-calming shape presented the most comfortable design for pedestrians and bicyclists. Sidewalk-level bike lanes were designed along the peanutabout’s perimeter, and raised crosswalks were created at pedestrian crossings. Emergency vehicles, large trucks, and buses are able to safely maneuver through each mini roundabout by driving over truck aprons and a smaller central island.

Intersection designs involving mini roundabouts, peanut-shaped roundabouts, and roundabouts with sidewalk-level bike lanes around the outside are relatively foreign in the U.S. The Inman Square intersection design—combining all of these elements—is the first of its kind in the country. If successful, the peanutabout could become an option in the toolbox of solutions for skewed intersections across the nation.

Read more about the Inman Square Peanutabout on KAI's Streetwise blog.