High motor vehicle speeds introduce significant risks to all road users by narrowing drivers’ fields of vision, requiring longer stopping distances, and increasing the likelihood of serious or fatal injuries when crashes occur.
Design streets to discourage unsafe motor vehicle speeds by minimizing excess motor vehicle capacity in both peak- and off-peak times. On streets near schools, nightlife destinations, and hospitals, vehicle volume and speed patterns will differ substantially from conventional peak commute patterns. When reviewing the existing conditions, consider the changes in speed and volume over the course of the day and the likely changes to those values that will result from the bikeway’s implementation.
Credit: City of Tucson
Traffic-Calming for Bikeways
Traffic-calming measures, coupled with appropriate bike facilities and intersection treatments, will enable lower-volume, lower-speed roadways that are safe and comfortable for people of all ages and abilities biking and walking.
Vertical deflection measures can be implemented as a periodic or “spot” treatment, or as a series. Spot treatments, such as raised crosswalks, can be found on all types of streets. These reduce vehicle speeds in the immediate vicinity of the intervention but are unlikely to affect speeds consistently along the block. A series of interventions, such as speed humps, will result in consistent, slower speeds–especially important for bike boulevards, advisory bike lanes, and constrained bike lanes. However, a series of speed humps or cushions are typically not appropriate on major streets that also serve as main routes for emergency services or transit.
Raised crosswalks and raised intersections can slow traffic at the ends of blocks as a gateway treatment, signaling that lower speeds are expected on the street. Raised crosswalks may also be used periodically as midblock elements to slow traffic near important community places, such as schools or parks.
Raised intersections and crosswalks should be the same height as the curb and extend fully from one curb to the other. The slope of the ramp up and down should be 7-8% relative to the existing slope of the street (See Unsignalized Intersections.)
Speed humps and speed cushions should be spaced regularly so that consistent, slow vehicle speeds are accomplished. Drivers should be able to see the next speed hump or cushion in the series as they pass over one. This will reduce the likelihood of rapid acceleration and deceleration between each speed hump or cushion. The specific distance between each hump or cushion depends on the street context, including block length, curvature, and grade. However, in most urban environments, the spacing should be 150-300 ft (45-90 m) with no more than 500 ft (150 m) between speed humps or cushions.
Speed humps and cushions should be constructed after planing 2 in (5 cm) from the roadway bed and result in a high point of 3-4 in (7.5-10 cm) above the pavement. Use sinusoidal curves on the approach and departure to enable smooth travel up and down the hump or cushion for bikes and other mobility devices. Speed cushions should be designed to fit the width of the street, typically resulting in cushions that are 7 ft (2.1 m) with gaps of 4 ft (1.2 m). Cushion design should allow bikes and specific vehicles, such as ambulances, to pass through but still prevent personal vehicles from passing without mounting at least one cushion.
Horizontal deflection techniques require vehicles to deviate from an otherwise straight path by changing the cross-section of the street. These techniques can be applied continuously along a street, as with chicanes, or at specific locations within each block, as with pinchpoints.
Pinchpoints, also called chokers or midblock hugs, are a pair of midblock curb extensions that purposely slow traffic or force a yield condition. They create a narrower path of travel for drivers, which causes most drivers to slow down. Pinchpoints on streets with curbside parking are most effective if the curb extensions are wider than the parking lane; if they are the same width as parked vehicles, the street is not narrowed and speeds will not be reduced. Pinchpoints slow traffic at their location; expect drivers to increase speed after passing through. As such, pinchpoints should be used in tandem with other traffic-calming techniques.
Chicanes narrow the traveled width of a street in an alternating pattern, forcing traffic to move in an “S” shape. Drivers must slow down to navigate these turns. Chicanes are often created by alternating curbs for on-street parking and/or using alternating curb extensions. Effective chicanes use a shorter taper length than typically required on streets. Ensure the horizontal deflection is wide enough to force drivers to deviate from a straight path.
Managing Vehicle Volumes
The frequency at which a person on a bike is passed by motor vehicles is one of the most useful indicators of the stress level of a roadway or bike facility. Maintain low motor vehicle volumes to minimize the number of times people on bikes are passed or overtaken.1 Volume reductions alone do not necessarily impact traffic speeds but will create an environment where all people on bikes will feel safer and more comfortable.
Drivers tend to be less aggressive and may be more likely to yield to people on bikes where there are no platoons or queues of motor vehicles. Once a platoon–even of two cars–exists, drivers pressure one another to continue moving. The driver in front experiences “back pressure” to continue while the driver(s) in the back may not see why the driver in front is slowing, creating an additional danger if they pass the front driver. They may be more likely to close-pass people on bikes or to fail to yield to people walking or bicycling.
Lowering vehicle volumes is often accomplished by changing the network role of a street, making it a non-through street for motor vehicles while preserving local access. When applying volume management to bikeways, monitor volumes on parallel streets to understand if complementary measures will be needed to reduce the potential impacts of rerouting.
Common methods for managing volumes include:
Designating routes for local traffic only. Simply signing streets for local traffic only is typically not successful nor equitable, as continuous enforcement is required. Instead, pair this designation with the implementation of a shared space design on one or several contiguous blocks. In these cases, hang advisory signs indicating a 10 mph (15 km/h) or under speed. Alternately, implement a shared space on a seasonal or recurring basis, as with play streets, market streets, school streets, or open streets events.2
Implementing a partial closure. Partial closures allow for people on bikes to travel in and out of a block but restrict one direction of travel for motor vehicles. Bidirectional motor vehicle traffic can be found within the block, but a small island or curb extension prevents drivers from entering the block.
Converting streets to one-way pairs. Evaluate the street network to identify two-way streets that connect to the same endpoints and are roughly parallel. In a grid, these streets are typically one block apart from each other, but a formal grid does not need to be present if the streets are generally within a ¼-mile (400 m) of each other.
Alternating street directions. Change the direction of a one-way street at an intersection, preventing through traffic from motor vehicles. This change can be made with only signs, though some drivers will disregard the signs if through-travel has been accommodated previously. Consider pairing this strategy with built changes to the intersection, including median or diverter islands, or hardening the centerline across the intersection with flex posts or jersey barriers.
Implementing “right-in/right-out” control. Channelize intersection movements by building islands that force drivers to turn right rather than continue through. Doing so reduces total motor vehicle volume and simplifies intersection movements. Design gaps to allow people on bikes to continue through.
Diverting both directions of travel. Build a diagonal island, or set of islands, across an intersection to require all motor vehicle traffic to turn at the intersection, regardless of the approach leg. Gaps in the island allow for people walking and biking to continue through.
Closing one end of a block. Disconnect a street from the network by preventing all motor vehicle traffic from entering or exiting the street, as with a cul-de-sac. Provide ramps for people on bikes to travel up and over the closure and allow permeability by emergency vehicles.
- On a 20-mph (30-km/h) street with 1,000 vehicles per day, a bike rider traveling at 12 mph (20 km/h) during peak hour would be passed by a car traveling in the same direction approximately every 86 seconds (assuming peak hour is 15% of vehicles per day, the street is two-way with 70% of traffic volumes traveling in the peak direction, and cars are evenly spaced along the street). By comparison, at 3,000 vehicles per day, a bike rider would be passed by a car every 29 seconds. At 5,000 vehicles per day, a rider would be passed by a car every 17 seconds. ↩︎
- National Association of City Transportation Officials. Streets for Pandemic Response and Recovery. NACTO, 2020. https://nacto.org/publication/streets-for-pandemic-response-recovery/ ↩︎