Design streets using target speed, a safe speed at which drivers should drive, rather than existing operating speed or statutory limit.
Align the design speed with target speed by implementing traffic calming measures, including narrower lane widths, roadside landscaping, speed cushions, and curb extensions. Traffic calming measures can be designed to slow general traffic while having little negative impact on transit vehicle operation.
Reducing speed dispersion confers a transit benefit by making traffic flow more predictable. In mixed-traffic operations, it is desirable for the 95th percentile of observed target speeds to fall within 5 mph of top transit speeds.
In selecting the design speed basis for such values as signal progression speed, lane width, and transition taper length, it may be appropriate to choose a speed lower than the speed limit, unless the limit can be lowered locally to the desired design speed. Using the full speed limit to calculate taper lengths, for example, can result in lane transitions occupying most of a city block, even though a less gradual transition self-enforces a safe design speed.
Where space is not highly constrained, it is desirable to provide longer (more gradual) horizontal and vertical transitions for transit vehicles, providing improved passenger comfort. Use standard lane widths to encourage safe operating speeds.
In-lane stops in mixed-travel lanes— which often utilize boarding bulbs and islands and stabilize operating speeds by reducing the need for transit vehicles to shift lanes—should be implemented where feasible (see Stop Placement & Intersection Configuration).
Reducing design speed using lower signal progression speeds can confer benefits to transit performance while improving safety for vulnerable users, especially in downtown contexts with closely spaced signals, or where dwell times are low but stops are frequent.
Shared transit streets may be assigned target speeds as low as 5–10 mph. At these speeds, rail vehicles or buses can operate safely in a traveled way shared by people walking.
Speed enforcement cameras have proven highly effective at reducing speeds and improving speed limit compliance by private motor vehicle drivers.