Lower Speed Limits

The speed of motor vehicle traffic has a clear impact on bicyclist safety (Helak et al., 2017; Peden et al., 2004). The goal of reducing motorist travel speeds is to increase reaction time for both drivers and bicyclists to avoid crashes, as well as reduce the severity of bicyclists’ injuries when these crashes occur. Reducing and enforcing speed limits is just one tool among many for decreasing travel speeds with the goal of improving bicyclist safety.

Speed limit reductions can be most effective when introduced to a limited area as part of a visible area-wide change, for example, identifying a downtown area as a special biking-friendly and walking–friendly zone through signs, new landscaping or “streetscaping,” lighting, etc. Road diets, an FHWA proven safety countermeasure, may be a low-cost way to reduce an overbuilt street that suggests high speeds to drivers and provide more space for walking, bicycling, and for drivers who need to park their vehicles.

If speed limits are routinely ignored, then enforcing speed limits may be a more effective strategy than attempting to change them. Blomberg and Cleven (2006) reported on demonstration programs in two cities in which speed limit enforcement, combined with engineering changes and extensive publicity, reduced both average speeds and the number of excessive speeders in residential neighborhoods. One attempt to scale up a similar program in Philadelphia met with challenges in garnering community involvement and increasing enforcement due to a State restriction on using radar to enforce speeds, and seemed to have limited success in reducing pedestrian injuries (Blomberg et al., 2012).

Use:

High, in the sense that all public roads have a speed limit and speed limit enforcement is widely employed, even if it is not with the express purpose of improving bicyclist safety.

Effectiveness:

Reduced speed limits with enforcement can reduce vehicle speeds and all types of crashes and crash severity. However, the measure of effectiveness for most studies of speed limit reductions or enforcement operations is speeds, not crashes or severity of injuries. Most of the research on the impact of speed reduction on vulnerable road user safety has focused on pedestrians. In Australia, an evaluation of crash data from two cities indicated that speed reduction was associated with a decrease in crash rates, but the effect was not the same in both locations, and incompleteness of available data meant it was impossible to perform robust statistical tests on the observed results (Kamruzzaman et al., 2019). Swedish researchers evaluated injury severity outcomes from crash data in Sweden, and results showed that people on bicycles had a much lower risk of severe injury at 30 to 40 kph (roughly 20 to 25 mph) compared to 50 to 60 kph (roughly 30 to 35 mph) (Isaksson-Hellman & Töreki, 2019).

Cost:

Simply changing speed limits is low-cost, only requiring updating speed limit signs or, where few signs exist, adding some new ones. Combining speed limit changes with communications and outreach, enforcement, and engineering changes is significantly more expensive.

Time to implement:

Depending on the scope of the program, the time can be very short, or it can take several months to more than a year, especially if legislative changes are needed.

Other considerations:

• Speed limit changes exist in the context of other, unchanged speed limits. The normal expectation is that there is an overall consistent approach to speed-limit setting. Where, for safety, some speed limits need to be reduced in a manner inconsistent with other speed limits, there must be clear and visible reminders that distinct conditions exist that justify the lower limits. Also, speed limit changes can be more effective if there is public buy-in, which involves a clear understanding of the reasons for the change.