Friday, July 19, 2024

June saw the deaths of two people riding bicycles in Cambridge. Both occurred at intersections and involved a turning truck. While we’ve seen a continuous decrease in the rate and severity of bike crash injuries in the city, these incidents underscore that there is more we should be doing, particularly at intersections.

While separated bike lanes are critical for safety on streets outside of intersections, intersections can also benefit from infrastructure safety improvements. In fact, the state’s Department of Transportation has a guide to designing safer intersections, and the National Association of City Transportation Officials also has a guide aptly named “Don’t Give Up at the Intersection.”

As the landmark Cycling Safety Ordinance is implemented, city staff have worked with stakeholders to design, refine and build separated bike lanes across the city. Among other safety benefits, these lanes can eliminate “dooring” crashes such as those that caused the deaths of Amanda Phillips in 2016 and Stephen Conley in 2022 in Somerville. When separated bike lanes arrive at most intersections in Cambridge, they often lose most of their physical protection.

City engineers can mitigate potential risks for vulnerable road users (people walking, cycling or using other non-car mobility devices) in several ways, with techniques specific to intersections. For example, they have used:

  • Daylighting, in which parking is moved away from areas close to intersections and crosswalks to make vulnerable road users more visible to people driving.
  • Turn hardening, in which corners of an intersection are extended to reduce their turning radius, encouraging turning vehicles to take turns more carefully.
  • Signal phasing, which can separate bike and vehicle movements in different signal phases to reduce conflicts between cyclists and vehicles.
  • Leading signal intervals, which Cambridge uses for pedestrian crossing lights and, in a few cases, for bicycles.

While these strategies are proven interventions that help reduce crashes, individually they are not enough to achieve the only acceptable number of serious injuries and deaths on the road: zero. According to the Safe Systems approach developed by the U.S. Department of Transportation, humans can be expected to make mistakes, and therefore redundancy is needed so one failure does not cascade into a tragic outcome.

A road user may not see or may ignore a red signal or prohibited turn sign. A driver may choose to park their car illegally in a bike lane or daylighting zone. While efforts should be made to reduce these occurrences, the design of our streets should prevent one failure or poor decision from becoming fatal. Cambridge should prioritize using a combination of these strategies in to add these critical layers of redundant safety.

Improved implementation: There are opportunities to improve some current implementations to increase their effectiveness. For example, bicycle signals must be visible and obvious to people traveling through an intersection for the first time. This is challenging, given that intersections vary widely across the city, so standardizing layouts as much as possible will be helpful.

Protected intersections: These extend the physical protection of the bike lane as far into the intersection as possible while incorporating elements such as signal separation, a reduced turning radius and better lateral separation between the bike lane and motor traffic.

Choice of materials for turn hardening: The city could make turn hardening more effective. For areas in which larger vehicles do not need to be accommodated, even more durable materials may be used. Daylighting and turn hardening materials must be durable and do their job of preventing vehicles from occupying the space. Flex posts may become damaged or destroyed after being driven over repeatedly. Many quick-build materials need constant monitoring and repair, or they will lose their effectiveness.

If you’d like to learn more about these techniques, see our more detailed summary with diagrams and photos.

We call on Cambridge to implement safer biking infrastructure across the city, including intersection safety improvements and the separated bike lanes needed to prevent deaths and injuries outside of intersections. Improved infrastructure can help prevent fatal crashes such as the ones this month – we must not wait for more deaths to make our streets safer.

Kevin Moses, on behalf of Cambridge Bicycle Safety