Speed Limit Legislation
ACT supports the proposed legislation to lower speed limits in Montgomery County. Speed kills. A pedestrian hit by a driver moving at 40 mph will die 90% of the time. If the driver is moving at 20 mph, the pedestrian will survive 90% of the time. These two bills thus represent a first step toward re-engineering our streets for safety.
We are concerned, however, about the provisions that maintain existing requirements for “traffic studies.” Traffic engineers often interpret this provision as mandating use of the so-called 85% rule to set speed limits. The 85% rule is rejected by safety experts.
The Federal Highway Administration says the 85% rule is a “myth” in its recently issued guidance document Achieving Multimodal Networks: Applying Design Flexibility and Reducing Conflicts. On roads where pedestrians are present, FHWA recommends instead that speed limits should be set using the “Safe Systems approach”:
The FHWA’s Methods and Practices for Setting Speed Limits states that
The Safe Systems approach, for instance, requires very little data collection since it is based on very basic road design parameters (e.g., number and frequency of accesses, presence of a raised median, etc.) and general traffic characteristics (e.g., type and frequency of road users). The data collection effort is relatively minor.
Montgomery County has adopted Vision Zero for road safety. As the two FHWA guidance documents state, the Vision Zero method of setting speed limits is the Safe Systems approach. Where pedestrians or cyclists are present, the only traffic studies necessary to set speed limits are the Safe Systems studies specified in the above quotation from FHWA’s Methods and Practices.
To avoid continued misinterpretation by traffic engineers, we therefore recommend deletion of the requirement for traffic studies from the legislation. The legislature should make clear that it does not endorse a so-called rule that is contrary to federal guidance.