Hampshire at Prospect Intersection Safety

• Serious crashes where a left-turning driver hits a pedestrian or cyclist have happened multiple times over the last ten years at every leg of this intersection.
• This project will add dedicated signal time for left turns on all approaches, meaning left-turning drivers will not have to look for gaps in oncoming traffic while checking that the crosswalk is clear before making their turns.

• Corner islands will be installed to slow right turns off of Mass Ave and one of the right turns off of Albany St.
• The islands will use flex posts and “bumblebee” devices and will be shaped differently based on available space.

• All walk signals will turn on five seconds before any driver sees a green light (a typical Pedestrian Head Start is three seconds).
• This extended head start lets pedestrians enter the crosswalk before drivers start turning right, making them easier to see.
• This treatment used in combination with the Corner Island treatment is expected to reduce the number of severe crashes between right-turning vehicles and pedestrians/cyclists.

• Some of the pavement markings in the intersection have faded and can be hard to see under certain conditions. We will refresh those markings when we install the new Corner Islands
• We will upgrade and verify the operation of APS push buttons to ensure they provide reliable crossing information for people with visual impairments. This makes it easier for those to cross.
• The mast arm (the pole holding the overhead signals) on the east corner of the intersection will be replaced as part of a longer-term capital construction project.

The Higher Crash Locations analysis performed by CDOT in 2025 used a crash reporting period spanning 2014-2024. During this time, there were three adjustments to the intersection of Hampshire Street at Prospect Street that affected safety and travel.

• In 2017, the City of Cambridge striped green cross bike markings on Hampshire Street.
• In 2021, Inman Square detours sent more traffic along Hampshire Street and a left-turn only lane was temporarily installed on Hampshire St southbound. Parking close to the intersection was also restricted, though this change was permanent.
• In 2023, the Hampshire Street Safety Improvement Project added separated bike lanes on Hampshire Street.

The graphic below details when various safety improvements were added to the intersection.

Because CDOT’s analysis period covers a few changes to the intersection, we expect that some of the earlier crashes at this location wouldn’t have happened or wouldn’t have been as serious if they had occurred after some of the intersection improvements were in place. However, crash analysis shows that certain crash trends have not been fully addressed yet.

This crash diagram shows all fatal crashes, crashes resulting in serious injury, and crashes involving pedestrians or cyclists from January 2001 to April 2025. The most noticeable trend is the high number of crashes involving a cyclist or pedestrian and a driver turning, especially turns from Prospect St to Hampshire St. With this trend in mind, this project focuses on having drivers turning proceed at a separate time than when pedestrians and cyclists are crossing the street (Time-Separated Turns). Where that is not possible, the project aims to make cyclists and pedestrians more visible while crossing and slowing vehicle turning speeds through Head Starts, Corner Islands, and Raised Centerlines. This project also prohibits a left turn that could not be time-separated.

Click here for a higher resolution.