Leading Pedestrian Intervals
Pedestrians are given a minimum head start of 3–7 seconds when entering the intersection.
Through and turning traffic are given the green light. Turning traffic yields to pedestrians already in the crosswalk.
Learn More About Leading Pedestrian Intervals
Application
A Leading Pedestrian Interval (LPI) typically gives pedestrians a head start of 3–7 seconds when entering an intersection with a corresponding green signal in the same direction of travel. LPIs enhance the visibility of pedestrians in the intersection and reinforce their right-of-way over turning vehicles, especially in locations with a history of conflict.
Use LPIs at intersections where heavy turning traffic comes into conflict with crossing pedestrians during the permissive phase of the signal cycle. LPIs are typically applied where both pedestrian volumes and turning volumes are high enough to warrant an additional dedicated interval for pedestrian-only traffic.
Benefits & Considerations
LPIs increase the visibility of crossing pedestrians and give them priority within the intersection.
LPIs have been shown to reduce pedestrian-vehicle collisions as much as 60% at treated intersections.1
LPIs typically require adjustments to existing signal timing that are relatively low in cost compared to other countermeasures.
Critical
LPIs are critical at intersections where heavy right or left-turning volumes create consistent conflicts and safety concerns between vehicles and pedestrians.
Recommended
LPIs should give pedestrians a minimum head start of 3–7 seconds, depending on the overall crossing distance. Intervals of up to 10 seconds may be appropriate where pedestrian volumes are high or the crossing distance is long.
To increase the effectiveness of an LPI and improve visibility of pedestrians at high-conflict intersections, install a curb extension at the intersection.
Optional
Where a bikeway on the through movement conflicts with turning traffic, use a leading bicycle interval along with the leading pedestrian interval. A leading bicycle interval clears the intersection of all cyclists quickly and can help prevent right hook collisions.
Split Phasing
Pedestrians and through traffic are given a green signal. Right and left turning vehicles are held at the intersection, effectively giving pedestrians a leading interval.
Right turning traffic is given the green light. Turning traffic yields to pedestrians already in the crosswalk.
Left turns lag with a dedicated signal phase. Pedestrians and through traffic are held to prevent head-on collisions and unpredictable movements.
Learn More About Split Phasing
Application
A split-phase signal design has multiple variations and applications, but is generally characterized by the separation of either all movements on opposite approaches, or of specific movements, such as left turns.
In an urban context, split-phasing is often used to mitigate left-turning hazards. Split-phasing can completely separate left-turning vehicles from crossing pedestrian movements, protecting pedestrians from unanticipated cross traffic and giving vehicles a dedicated left-turn phase.
Split-phasing is most often applied in the following situations:
- Intersections with history of side swipe or head-on collisions between left-turning vehicles, potentially resulting from geometric constraints or shared left-turn and through lane configuration.
- At locations where pedestrians may feel inundated at the intersection by both right and left-turning traffic, such as highway on ramps.
- Where a large skew at an intersection poses a serious risk to oncoming vehicles or pedestrians and may be functionally enhanced through separation.
Benefits & Considerations
Split-phasing can help reduce the overall risk of pedestrian injury and decreases the potential for head-on vehicle collisions.
Reduces lost time for traffic proceeding straight through the intersection.
Use of split-phasing may increase the overall signal cycle length, reducing the overall time available for pedestrian crossings and increasing wait time for all movements.
While split-phasing operations bear consideration in certain locations, a city may elect to restrict left turns entirely or for specific portions of the day when risk of collision is most acute, as an alternative.
Protected Left Turn Phasing
At locations where left turning motorists pose a significant threat to through traffic, pedestrians, and bicyclists, left turns can be given a protected phase.
Learn More About Protected Left Turns
Application
Protected left-turn phasing is most often applied in the following situations:
- Intersections with a history of collisions between left-turning and through vehicles, potentially resulting from geometric constraints or heavy conflicting volumes;
- at locations where pedestrians or cyclists may experience risk associated with left turning traffic relying on the acceptance of gaps;
- and where a large skew at an intersection poses a serious risk to oncoming vehicles or pedestrians and may be functionally enhanced through separation
Benefits & Considerations
Protected left-turn phasing can help reduce the overall risk of pedestrian injury and decreases the potential for crashes.
Use of protected phasing may increase the overall signal cycle length, reducing the overall time available for pedestrian crossings and increasing wait times for all movements.
While protected left turn phasing bears consideration in certain locations, a city may elect to restrict left turns entirely or for specific portions of the day when risk of collision is most acute (see below).
Left Turn Restrictions
Restricting left turns eliminates the conflict between left turns, oncoming motorist and bicyclist through traffic, and pedestrians. These restrictions may shift the conflict to a more desirable location along the corridor and have been successfully implemented by time of day in many cities.
Learn More About Left Turn Restrictions
Application
Eliminating left turns at an intersection is most often applied in the following situations:
- Intersections in a grid network of streets with adjacent intersections better able to handle additional phases in the signalized intersection (depending on block length);
- at locations where pedestrians or cyclists may experience risk associated with left turning traffic;
- and intersections where crossing traffic is significantly high and person carrying capacity may be a higher priority than local automobile accessibility.
Benefits & Considerations
Left turn restrictions can help reduce the overall risk of pedestrian injury.
Eliminating a left turn movement at a particular location reduces the total lost time for the intersection, thus increasing the person carrying capacity of the intersection and reducing the overall cycle length.
Left turn restrictions reduce the conflict between through moving traffic and left turns, improving overall safety at intersections.
Restrictions can be managed by time of day, though time of day restrictions may require additional enforcement and adequate signage to ensure comprehension.
- A.C. Fayish and Frank Gross, “Safety effectiveness of leading pedestrian intervals evaluated by a before–after study with comparison groups,” Transportation Research Record No. 2198 (2010): 15–22. ↩︎