Bikeway design permits practitioners to reassess the priorities of an intersection and improve its organization. In creating better bikeway intersections, designers can consolidate motor vehicle lanes, move motor vehicle turns to more manageable locations, and convert motor vehicle areas into pedestrian or bike safety features.
These changes improve safety by clarifying where each person should be located within the intersection at a given time and by allowing more time for people on bikes and approaching drivers to notice one another and adjust their trajectories as needed.
Designers should address the specific needs of an intersection while also considering strategies to reduce overall motor vehicle speeds on the street through traffic calming measures such as the use of stop signs or roundabouts instead of signals, signal progressions designed to limit opportunities for speeding, lane narrowing, lane reorganization, or lane reallocation to non-vehicular uses.
Start the design process by critiquing the purpose of the intersection within the motor vehicle, transit, bikeway, and pedestrian network. If the current geometric and signal timing priorities conflict with the adopted modal and safety policies, take the opportunity to realign the intersection design with the adopted policies.
Use the Appropriate Design Vehicle
The managed vehicle, the design vehicle, and the control vehicle inform the design of the corner radius at an intersection and the need for vertical features to manage speeds. Using the appropriate vehicles will result in shorter crossing distances, safer intersection designs, and the maximization of space for people walking or biking.
Managed Vehicle
Typically a passenger car or light truck, the managed vehicle is the most common vehicle to use the street. It is capable of higher turn speeds than a design vehicle, is driven by a non-professional driver, and is likely to be involved in most crashes. The managed vehicle should be able to turn slowly from within its lane without traversing any truck aprons or vertical elements.
Intersection design should discourage a managed vehicle from turning faster than 5-10 mph (8-16 km/h). This can be accomplished with a turn radius of less than 18 ft (5.4 m), usually resulting from a 10-15 ft (3-4.5 m) curb radius with narrowed or hardened receiving lanes.
Design Vehicle
The design vehicle is the largest regular vehicle that will frequently use the street, typically a delivery truck (DL-23) or single-unit truck (SU-30). Design vehicles must not encroach into pedestrian or bike waiting areas during the turn movement. If a scheduled or planned bus route turns at the intersection, then a city bus should be used as a design vehicle for the relevant corner. A car, light truck, or delivery van should be used as the design vehicle in a residential setting, allowing for a tighter turn radius.
Bikeway intersection design should accommodate a design vehicle turning at 3-5 mph (4.8-8 km/h).
Design vehicles should be allowed to use all of the first lane of the receiving street and part of a second or opposing lane. They are expected to traverse marked buffers and mountable elements such as a truck apron or hardened centerline.
Control Vehicle
The control vehicle is the largest vehicle that will infrequently use the street. A WB-50 truck or an aerial ladder fire truck should be used for major streets and downtown settings. In residential settings, use a fire engine.
The control vehicle should be expected to turn at a very low or ‘crawl’ speed of 1-5 mph (1.6-8 km/h). Field testing or observation could be desirable for turn speeds under 5 mph, as software may be inaccurate at low speeds.
The control vehicle should be expected to traverse mountable elements while turning, enter the lane adjacent to its lane of origin, and/or overtrack the centerline of the intersecting street. Where necessary, set stop lines back to accommodate this encroachment. This strategy allows much larger vehicles to be accommodated without compromising the critical function of turn speed management.
While emergency vehicles can be used as control vehicles, they should also be given more flexibility to overtrack or cross into other lanes. Emergency vehicles operate in unique circumstances, often with lights and sounds that alert other road users to move out of the way. Assume that emergency vehicles can use the full width of the roadway, even in the opposing direction, and can encroach on pedestrian and bike space. In some cases, the bikeway may function as a queue jump for ambulances and smaller fire trucks.
Turn Encroachment
| Approach | Corner Elements or Roundabout Center Island | Receiving Street Lane Line | Receiving Street Centerline | |
| Managed Vehicle | No encroachment. | No overtracking is necessary. | No encroachment. | No overtracking. |
| Design Vehicle | Encroachment is acceptable within the same direction of travel. | Overtracking of mountable corner or truck apron is expected.No overtracking of pedestrian space or protected bike space is allowed. | Encroachment within the same direction of travel is expected. | Overtracking permitted. |
| Control Vehicle | On arterial streets, may use the full approach width within the same direction of travel. On collector or local streets, may approach into opposing flow on local streets. | Encroachment within the same direction of travel is expected. | On arterials, minor overtracking into opposing flow is expected. On collector or local streets, overtracking into opposing flow is expected. |
Reduce Intersection Complexity
Safe intersection design is challenging in complex urban environments. Trade-offs between modes and movements must be made. Along bikeways, designers must look beyond bikeway design to ensure safety for everyone in the intersection.
Restrict turns. Consider relocating challenging turns to alternate locations. Motor vehicle turns consume a large amount of lane space and signal time, rendering that time unavailable for people biking or walking and for other types of vehicular movement in the intersection. If phase separation isn’t feasible at a particular location, restrict turns and explore rerouting to other intersections.
Reduce or eliminate skew. Streets that end at a skewed intersection should be evaluated for realignment, even if only with markings and flexible materials. Curb extensions and channelization can be used to make vehicle approaches meet the intersection closer to a right angle. At large skewed intersections, realign turn lanes to meet the intersection at closer to 90 degrees1 where possible without creating channelized right turn lanes. Evaluate the potential for turn restrictions to simplify operations and improve safety.
Re-evaluate turn lanes and signals. Motor vehicle turn lanes can help organize traffic and create a safe place for drivers to wait while yielding to people biking and walking. When combined with signal separation, turn lanes are an important tool for managing high-volume motor vehicle turn movements across bikeways. High-volume turns, left turns across multiple lanes, or turns on higher-speed streets generally require signal separation from bikeway traffic. Turn lanes increase exposure and crossing distance for people on bikes and on foot and can increase turn speeds, thereby creating less safe intersections. Evaluate if the turn lanes provide tangible safety benefits for people walking and biking or help improve transit times. Where turn volumes allow, eliminate turn lanes in favor of providing space for bikeways, protection islands, or sidewalk extensions. (See Design Strategies for Signalized Intersections.)
Eliminate right-turn slip lanes. Right-turn slip lanes, often separated by triangular ‘pork chop’ islands, require larger intersections and allow higher-speed turn movements. These are difficult for pedestrians to cross, particularly when the right turn movement is not signal-controlled.
Re-evaluate the necessity of slip lanes by tolerating slightly longer vehicle delays. Reallocate this space to the bikeway, creating a bend-out intersection. Consider using a portion of that space for a sidewalk extension in projects with minimal construction. Where a slip lane is necessary, such as intersections with acute approach angles, control the slip lane with a STOP (MUTCD R1-1) sign or traffic signal.
- “Results of this study showed that a 90-degree intersection angle is associated with the lowest expected number of crashes.”
Federal Highway Administration. Impact of Intersection Angle on Highway Safety. Publication Number FHWA-HRT-20-067. USDOT, 2021: page 95. https://www.fhwa.dot.gov/publications/research/safety/20067/20067.pdf. ↩︎