Design Tools for Intersections

Curb Extensions

• Slows turns and manages speed
• Increases visibility

Curb extensions, also known as bulbouts, improve sightlines and provide expanded pedestrian space. When designed with tight curb radii, they reduce turn speeds and improve safety. Constructed curb extensions are durable and provide space for green stormwater infrastructure. They can also be designed with flexible materials, such as delineator posts and colored surfacing; in this form, they are called sidewalk extensions.¹

Crossing Islands

• Slows turns and manages speed
• Increases visibility

On multilane streets, crossing islands divide the crossing process into two stages and provide a safe waiting space. This allows people walking and biking to focus on one direction or lane of traffic at a time, making it easier to cross the street. Crossing islands encourage slower, safer turns as drivers must turn at angles closer to 90 degrees. Crossing islands are especially important for bikeways on minor streets or paths that cross major streets. 

Crossing islands should be at least 6 ft (1.8 m) wide, allowing for the placement of a DWS on both edges and clear space in between. Where possible, widen crossing islands to 10 ft (3 m) to better accommodate cargo bikes, bikes with trailers, and large groups. Constructed islands can also feature green stormwater infrastructure.

Crossing islands can be implemented with flexible materials, such as markings, delineator posts, and signs. Use of DWS is optional.

Crossing islands can be supplemented with RRFBs, hybrid beacons, half-signals, or conventional signals.

Raised Intersections

Slows turns and manages speed

Raised intersections provide a high-comfort, low-speed space for people walking and biking to cross an intersection. They are flush with the sidewalk and require a DWS and/or TDI for non-visual navigation to crossings. The approach and departure slope should be at least 7-8% relative to the existing slope. Use the smallest possible curb radius when constructing raised intersections on smaller residential streets, typically 5-10 ft (1.5-3 ft).

Bollards may be placed at corners to help prevent drivers from turning into the pedestrian space. Avoid creating challenging conditions for people using wheelchairs when placing bollards.

Provide crosswalks and crossbikes over the raised intersection. Avoid using unit pavers within crosswalks and crossbikes as the uneven surface is jarring for people using wheelchairs, scooters, and other devices with small wheels.

Approach Speed Humps

• Slows turns and manages speed
• Increases visibility

Approach speed humps reinforce the primacy of bikeways by slowing traffic on cross streets just before intersections. An approach speed hump is a low-cost retrofit option that does not impact drainage or require ramp reconstruction. Build a speed hump within 50 ft (15 m) of the intersection. Approach speed humps are typically placed on lower-volume streets and accompanied by stop control at the intersection. They may be used along bike boulevards, advisory bike lanes, or constrained bike lanes. Avoid using approach speed humps on main streets with frequent bus service. (See Vehicle Speed and Volume Management.)

Raised Bikeway Edges

Slows turns and manages speed

The edge of a bikeway can be raised using a speed bump or a gently raised area similar to a speed hump where other turn-calming treatments, such as tighter curb radii or raised crossings, cannot be installed. Consider raised bikeway edges for minor streets, driveways, or alleys with higher percentages of heavy vehicles

Use a speed bump, or a line of modular speed bumps, along the edge of constrained, buffered, or protected bike lanes where they pass along a minor street, or a busy driveway or alley. Speed bumps make bikeways more conspicuous and slow turn speeds. Mini speed bumps are usually 2 in (50 mm) high and made of rubber. They require regular repair or replacement, particularly in wintry climates where snow plow blades may dislodge them.

Along parking-protected bike lanes with corner islands, gently raise the street by 3-4 in (75-100 mm) between the travel and bike lanes to slow speeds. Depending on the location, this design may not require modification for drainage. The raised section, similar to a speed hump, should be designed to the desired motor vehicle turn speeds of 5-10 mph (10-15 km/h). Use a sinusoidal profile to improve comfort for people on bikes who may ride over the raised area.

Raised Crossings

• Slows turns and manages speed
• Increases visibility

Raised crossings reduce motor vehicle speeds, increase yielding behavior, and improve the visibility of people on bikes and foot. They can reduce pedestrian crashes by 45%.²

Raised crossings should be the same height as the sidewalk. The approach and departure slope should be at least 7-8% relative to the existing slope. The top of the raised crossing should be flat with distinct markings for the crossbike and the crosswalk. Use DWS only for the pedestrian path of travel.

Street-level or intermediate-level bikeways must slope upward to meet the raised crossing approaching an intersection. (See Bike Transitions.)

Providing a shared raised crossbike and crosswalk is preferred where project scope and budget allow. If the crossbike cannot be raised, a raised crosswalk is still beneficial in reinforcing slower speeds, enhancing accessibility for people with disabilities, and improving pedestrian safety. 

Corner Islands

• Slows turns and manages speed
• Increases visibility
• Reduces conflicts

Corner islands extend the bikeway protection into the intersection by reducing right turn speeds and improving yielding to people biking and walking.³ They also enhance the bikeway’s comfort by preventing motor vehicle drivers from encroaching into the bikeway.

The corner island should limit managed motor vehicle turn speeds to 10 mph (16 km/h) or less.⁴ The target effective turn radius for managed vehicles is less than 18 ft (5.4 m), usually resulting in a corner radius of 10-15 ft (3-4.5 m).

Corner islands are subject to overtracking by some vehicles; construct with concrete where feasible. Flexible materials can be used to create corner island treatments⁵ but will require more frequent repair or replacement. (See Slow Turns Are Safe Turns.)

Pedestrian Islands

• Slows turns and manages speed
• Increases visibility
• Reduces conflicts

Pedestrian islands along protected bike lanes provide space for people walking to wait before or after crossing the bike lane. They allow pedestrians to negotiate crossing bike lanes separately from general travel lanes and reduce exposure when crossing the street. They also help reduce right turn speeds, add visibility for drivers, and protect the bikeway at intersections.

Pedestrian islands should be fully traversable without ramps. The opening in the island should match the width of the crosswalk, typically 8-12 ft (2.4-3 m). Pedestrian islands should be at least 6 ft (1.8 m) wide, allowing for the placement of a DWS on both edges with clear space in between. Narrower islands still provide benefits but should not feature DWS.

Protected Bike Lane Approaches or Departures

• Slows turns and manages speed
• Reduces conflicts

A short protected bike lane approach organizes the intersection, gives people on bikes a place to wait out of the flow of motor vehicle traffic, and reduces turn speeds. They are especially beneficial for contraflow lanes but should also be considered where shared, constrained, or buffered bike lanes approach controlled intersections.

Protected bike lane approaches and departures can be constructed islands, feature mid-height barriers, or be implemented with flexible materials such as curb stops and flexible delineator posts.

Hardened Centerlines and Lane Lines

Slows turns and manages speeds

Use centerline and lane line hardening to reduce turn speeds, control turning paths, and prevent lane changes near crosswalks or crossbikes. Mountable concrete curbs or 2 in (50 mm) high modular speed bumps are commonly used for areas that motor vehicles need to traverse. Curbs or flexible delineators are used for areas that do not need to be traversed.

Hardened Centerline Diverter

• Manages volumes
• Reduces conflicts

Use hardened centerline diverters, such as concrete, flexible delineators, or plantings, placed on the centerline of the intersecting street to prevent vehicular traffic from continuing through on a bikeway. Vehicular traffic must turn upon exiting.

Provide adequate openings to allow people on bikes to pass through. This treatment does not give bikeway users space to wait and stage their crossings.

Alternating Street Directions

Slows turns and manages speeds

On streets with bikeways, change the street direction at an intersection to have opposing one-way travel for drivers. Vehicular traffic can turn in either direction but cannot continue straight. Drivers on the cross street cannot turn onto the street with the bikeway.

People on bikes and other devices are accommodated with directional crossbikes and short, receiving-side protected bike lanes.

Center Bikeway Diverters

• Manages volumes
• Reduces conflicts

At right-in-right-out intersections, a center diverter doubles as a queuing area for people on bikes. An approach center bike lane can be provided, even if people on bikes are mixed into general traffic on either side of the diverter. Provide adequate room on the approach and departure for bikeway users to safely merge into general traffic.

Diagonal Diverters

• Manages volumes
• Reduces conflicts

Diagonal diverters placed at a four-way intersection require all motor vehicles to turn while allowing people walking or biking to continue through the intersection unimpeded. 

Install a 6-10 ft (1.8-3 m) refuge area for people on bikes who wish to cross to wait for a gap in traffic. Offset the vertical elements of the diverter from the curb to allow people on bikes to turn right. This will also limit the potential impact on drainage. 

Diagonal diverters can be implemented with planters, flexible delineators, and other modular materials.