Design Strategies for Signalized Intersections

Signalized intersections provide additional opportunities to improve safety by separating bikeway users from vehicular traffic with time. Through a combination of signal phasing and geometric design decisions, signalized intersections can provide safe, comfortable, and predictable movements for everyone–whether driving, walking, biking, or rolling. Designing signal phasing and timing and intersections to minimize interactions between drivers and people biking can create facilities that are comfortable for a wide array of people.¹

Use Geometric Design to Mitigate Conflicts

Dedicated and protected intersections have been implemented across North America as cities expand their bikeway networks. By combining multiple design tools, these intersections protect bikeway users from rear-end crashes, sideswipe or merging crashes, and crashes with cross-traffic. They also reduce pedestrian exposure to crashes. 

Both dedicated and protected intersections are appropriate along one- and two-way bikeways and should be applied to all major signalized intersections along a bikeway. They are particularly beneficial at intersections with moderate-to-high traffic volumes or speeds, heavy turn volumes, or a higher percentage of heavy vehicles.

At intersections with a high number of vehicles turning over the bikeway, use signal phasing to prohibit conflicting movements. Separating conflicting movements becomes more important where there is limited setback for the bikeway.

Dedicated Intersections

Dedicated bikeway intersections offer a marked improvement over mixing zones or constrained bike lanes alone by providing excellent visibility and low turn speeds. The bikeway is physically separated from motor vehicles up to the intersection and the approach visibility zone is clear to allow mutual observation between people on bikes and drivers. Dedicated intersections can be implemented at signalized, stop-controlled, and unsignalized intersections with small geometric variations. 

Bikeway separation may be wide enough to allow for a pedestrian island. Where possible, set the crosswalk back from the intersection to allow bikeway separation to continue to the corner. This protects pedestrians using the crosswalk from turning drivers and helps to slow vehicular turning speeds across the bikeway. 

In constrained conditions, use flexible materials, such as modular speed humps and markings, to create a small corner wedge that can slow turns and improve yielding. Corner wedges can be placed in the vehicular swept path but not in the bikeway crossing.

Bikeway users have a dedicated path through the intersection and the right of way over turning motor vehicles. Provide crossbike markings to increase the bikeway’s conspicuity through the intersection. (See Don’t Give Up at the Intersection.)

In multilane intersections, supplement the corner island with centerline or lane line hardening. These elements encourage drivers to turn directly into a single receiving lane instead of turning over a lane line and improve safety for people walking and biking across intersections.²

At intersections with a high number of vehicular turns over the bikeway, use signal phasing to manage conflicting movements safely. (See Signal Phasing and Timing Strategies.)

Provide accessible curb ramps with Detectable Warning Surfaces and Accessible Pedestrian Signals. Accommodate people waiting to cross on the sidewalk before they cross the bike lane. Ensure pedestrian islands located between the bikeway and travel lanes meet accessibility requirements, as applicable.

Protected Intersections

Protected intersections keep bikeway users physically separate from motor vehicle traffic up to the intersection, providing a high degree of comfort and safety for people of all ages and abilities.^3,4 An approach visibility zone allows people on bikes to observe parallel motor vehicles and drivers to observe people approaching in the bikeway.

Notably, the bikeway is set back from the parallel motor vehicle traffic in protected intersections. The setback between the motor vehicle lane and the bikeway is typically 10 ft (3 m), providing a place for drivers to wait before turning across the bikeway. 

A corner island separates bikes from motor vehicles, prevents motor vehicles from encroaching on the bikeway, and creates a protected queuing area for people on bikes or other micromobility devices. Minimize the corner radius to slow turn speeds. The corner island should limit managed motor vehicle turn speeds to 10 mph (16 km/h) or less. (See Slow Turns Are Safe Turns.)

The setback and corner island work together. People on bikes are more visible to turning drivers and they have more time to notice and react to turning vehicles. 

Bikeway users have a dedicated path through the intersection and the right of way over turning vehicles. Provide crossbike markings to increase the bikeway’s conspicuity through the intersection. (See Don’t Give Up at the Intersection.)

In multilane intersections, supplement the corner island with centerline or lane line hardening. These elements encourage drivers to turn directly into a single receiving lane instead of turning over a lane line to improve safety for people walking and biking across an intersection.⁵

Provide accessible curb ramps with Detectable Warning Surfaces and Accessible Pedestrian Signals. Accommodate people waiting to cross on the sidewalk before they cross the bike lane. Ensure pedestrian islands located between the bikeway and travel lanes meet accessibility requirements, as applicable.

Protected intersection designs are not always possible. They require more space within the intersection and typically need significant capital investment in constructing islands and moving curbs. On high-activity, walkable downtown streets and neighborhood main streets with narrower sidewalks, the potential for more sidewalk space may outweigh the benefits of setbacks and corner islands. In other cases, the existing right-of-way may not be sufficient for a protected intersection. Dedicated intersections and bike-friendly signal timing provide many of the same safety and comfort benefits as protected intersections.

Balancing Safety and Operational Needs

Signal phasing and timing are core tools for better intersection design. Trade-offs between comfort and convenience are present in all signal operations. Operational analysis informs, but does not predict, how to phase a signalized intersection. Intersection and corridor signal timing analysis, the existing risks and operational issues at an intersection, and an understanding of how people using the street will respond to signals are all important factors in operations decisions.

Along bikeways, signal plans should:

Removing Conflicts May Increase Delays

Trade-offs between comfort and convenience are inherent to decisions about separating conflicting bike and motor vehicle movements. 

Motor vehicle turning movements consume a large amount of time and space at intersections. At the same time, people on bikes express a comfort preference for protected bike signal phases with separate motor vehicle turn phases. However, in many urban intersections, fully separated phases will result in longer wait times for everyone: people on bikes, people walking, and those traveling by bus or private automobile. This can lead to non-compliance.

To limit delays for people using the bikeway:

• Prioritize short cycle lengths, including using half-cycles.
• Minimize the turn phase while maximizing the bike phase, increasing the percentage of cycle length dedicated to bike movements.
• Use an actuated turn phase rather than running it on recall.
• Coordinate signals to operate at or near bike speed rather than the vehicular speed limit, allowing people on bikes to arrive at intersections just before or during the green phase.
• Install bike detection ahead of the intersection to call or extend the bike green for people riding in the bikeway.
• Overlap bike and pedestrian movements with complementary motor vehicle turn phases.
• Prohibit vehicular turns entirely.

Where delays are excessive, it is more effective to provide flexibility to people walking and biking, such as allowing them to proceed even after motor vehicles begin to turn across the bikeway. Geometric design elements, such as corner islands or wedges and lane line hardening, should be used where permissive vehicular turns across the bikeway are allowed.

Shorter Cycle Lengths

Shorter signal cycle lengths have operational advantages for bikeways and other urban streets. With more opportunities to cross the street and shorter wait times, signal compliance by all users tends to increase, reducing the risk of fatal and injurious crashes. 

Shorter cycle lengths also reduce exposure to turning vehicles. Though the same total number of drivers may turn, fewer turn during any given green phase. As a result, phase separation may not be necessary for safety.

While shorter cycle lengths result in lower vehicle throughput per cycle, they also result in shorter, more manageable motor vehicle queues. Shorter cycle lengths can improve motor vehicle operations when turns make up a high percentage of total vehicle movements.

Prohibit Left-Turn Movements 

Finding a safe time within a cycle for motor vehicles to turn can be challenging at complex or high-volume intersections. Left turns across bikeways at signalized intersections on two-way streets pose special safety concerns for people on bikes. Drivers turning left use most of their decision-making capacity to find a gap in oncoming vehicular traffic. People in the bikeway or crosswalk are the last consideration.

Analyze intersections along the corridor to determine if turns can be rerouted to other intersections within a reasonable distance. Alternatively, look for opportunities to convert a left turn into a series of right turns.

Rerouting left turns can also improve operations for transit vehicles and through vehicles.

Mitigate Impacts to Transit

Protected right-turn phases may be needed in locations where bus routes turn right due to sightline challenges between right-turning buses and through bikes. Phase separating these turns can affect transit operations at high-volume turn locations if the right turn queue is long. However, phase separation is also an opportunity to provide transit vehicles with a leading interval at the same time as parallel bikes. Bending the bikeway out toward the sidewalk to create a larger setback can minimize the time a person biking is outside the view of the bus operator and, in some contexts with low turn volumes, may be an alternative to phase separating the right turn. 

Creating a dedicated right-turn phase along transit routes may negatively affect turning capacity and through movements by transit vehicles. When a bus needs to serve a nearside stop, it may block right-turning vehicles during the entire right-turn phase. Alternatively, a bus may be delayed if it has to wait in a right-turn queue before reaching the stop. Relocating the bus stop to a farside or midblock location can help mitigate these operational challenges but may result in other undesired outcomes, such as longer walking distances for transfers or less crosswalk compliance.

1. Monsere, Christopher M., et al. Contextual Guidance at Intersections for Protected Bicycle Lanes. Publication Number NITC-RR- 987. National Institute for Transportation and Communities, 2019. https://doi.org/10.15760/trec.241.  ↩︎
2. New York City Department of Transportation. “Don’t Cut Corners: Left Turn Pedestrian and Bicycle Crash Study.” NYCDOT, 2016. https://www.nyc.gov/html/dot/downloads/pdf/left-turn-pedestrian-and-bicycle-crash-study.pdf. ↩︎
3. Monsere, Christopher M., et al. Contextual Guidance at Intersections for Protected Bicycle Lanes. Publication Number NITC-RR- 987. National Institute for Transportation and Communities, 2019. https://doi.org/10.15760/trec.241.  ↩︎
4. Madsen, T.K.O., and H. Lahrmann. “Comparison of five bicycle facility designs in signalized intersections using traffic conflict studies.” Transportation Research Part F: Traffic Psychology and Behaviour 46, pt. B (2017): 438-450. https://www.sciencedirect.com/science/article/pii/S1369847816300705. ↩︎
5. New York City Department of Transportation. “Don’t Cut Corners: Left Turn Pedestrian and Bicycle Crash Study.” NYCDOT, 2016. https://www.nyc.gov/html/dot/downloads/pdf/left-turn-pedestrian-and-bicycle-crash-study.pdf.  ↩︎
6. “96% of drivers approaching a bicyclist yielded and 100% of drivers approaching a pedestrian yielded.”
   San Francisco Municipal Transportation Agency. “9th and Division Street Protected Intersection Fact Sheet.” SFMTA, 2017. https://www.sfmta.com/sites/default/files/reports-and-documents/2018/03/9th_division_fact_sheet.pdf.  ↩︎
7. “The Fully Split Phase location has the lowest conflict rate for the higher scoring (conflict scores 2-4) conflicts.” Cycling at a Crossroads: The Design Future of New York City Intersections. NYCDOT, 2018. https://www.nyc.gov/html/dot/downloads/pdf/cycling-at-a-crossroads-2018.pdf.  ↩︎
8. “Close calls where drivers or bikes/pedestrians had to abruptly yield to avoid a collision reduced 11-fold from about 9 an hour to less than one an hour.”
   Oakland Department of Transportation. “Lake Merritt BART Intersection Improvements Evaluation Report.” OakDOT, 2020. https://cao-94612.s3.amazonaws.com/documents/Lake-Merritt-BART-Intersection-Improvements_V4.pdf.  ↩︎
9. Dunn, M. R., et al. “Data-Driven Methodology for Prioritizing Traffic Signal Retiming Operations.” Transportation Research Record 2673, no. 6 (2019): 104–113. https://doi.org/10.1177/0361198119843236. ↩︎