In a previous article, we outlined the benefits and limitations of signal coordination and the circumstances under which signal coordination can be an effective traffic management strategy. Here, we want to continue the discussion on traffic signals, this time focusing on signal timing for pedestrians and bicyclists, and highlighting traffic signal control strategies that make traffic signals more friendly for people on two feet and two wheels.
In the United States, traffic signal timing is traditionally developed to minimize vehicle delay at signalized intersections. This often results in degraded safety and mobility for pedestrians and bicyclists. The issue is further exacerbated by the lack of available tools that calculate pedestrian and bicyclist delay at signalized intersections. Software tools typically used for signal timing do not calculate pedestrian and bicyclist delay which results in disproportionately high delay and poor user experiences.
Traffic signal timing is traditionally developed to minimize vehicle delay at signalized intersections. This often results in degraded safety and mobility for pedestrians and bicyclists.
How can we overcome these challenges and ensure traffic signals do not create barriers for pedestrians and cyclists while maintaining the need for vehicles? Enter NCHRP Research Report 969, which we authored along with Peter Furth, Ray Saeidi-Razavi, and Janet Barlow. This research developed new performance measures for pedestrians and cyclists and a toolbox of treatments at signalized intersections to improve pedestrian and bicyclist experiences by elevating safety considerations, reducing their delay, and enhancing accessibility. It describes two performance measures and 28 unique treatments to make intersections more friendly for pedestrians and cyclists. Read on to learn more about each!
While pedestrian delay is an easy-to-calculate metric (especially when crossings are not two-stage) and should be one of the primary objectives in intersection design, it is often ignored. Not reporting pedestrian delay, if computed, can lead to situations where average intersection vehicle delay is as low as 20 seconds while average pedestrian delay is as high as 80 seconds (e.g., for actuated pedestrian crosswalks crossing a mainline).
High pedestrian delays also create an environment with increased safety challenges. The Highway Capacity Manual (HCM) 2000 indicates that when average pedestrian delay is larger than 60 seconds, very high likelihood of non-compliance is anticipated. As a result, NCHRP Research Report 969 advises considering pedestrian delay as part of an intersection analysis along with vehicle delay (and average bicycle delay can be approximated by the pedestrian delay where bicycles follow a pedestrian phase). The simple action of reporting pedestrian delay raises the practitioner’s awareness of intersection performance and as a result, can identify opportunities to improve the condition.
Lowest Pedestrian Speed Accommodated
Another metric we produced in our research is the lowest pedestrian speed accommodated for a given crosswalk. According to the Manual on Uniform Traffic Control Devices (MUTCD), a walking speed of 3.5 feet per second should be used to calculate pedestrian clearance time for pedestrians who begin crossing up to the last moment of the Walk interval. However, research that studied walking speed distribution among different age groups showed that about 8 percent of adults 60 and younger and 26 percent of adults older than 60 years old walk slower than 3.5 feet per second.
Intersection timing should meet the needs of most users by accommodating lower pedestrian speeds, thereby increasing intersection accessibility. To help agencies during signal timing development and incentivize timing plans that can accommodate lower walking speeds, NCHRP Research Report 969 provides methods to calculate lowest pedestrian speed accommodated at a signalized intersection as a way of quantifying accessibility.
Toolbox of Treatments for Pedestrians and Bicyclists at Signals
In addition to the two metrics described above, NCHRP Research Report 969 describes a toolbox of treatments to better address the needs of pedestrians and bicyclists at signalized intersections. For the purposes of this research, the treatments are organized based on intended outcome:
Reduce or eliminate conflicts with turning traffic: Includes nine treatments to address conflicts with turning traffic, some to reduce conflicts (e.g., leading pedestrian intervals, also known as LPIs, delayed turns), and others to eliminate conflicts (e.g., protected only turns).
- Reduce pedestrian and cyclist delay: Includes six treatments to reduce pedestrian and cyclist delay at intersections (e.g., short cycle lengths, reservice) and accommodating slower pedestrians (e.g., maximizing Walk interval length).
- Address special bicycle needs: Offers six treatments to address needs specific to bicyclists including change interval settings, signal progression, and detection (e. , minimum green and change interval settings for bicycle clearance, two-stage left turn progression for bicycles).
- Provide added information and convenience: Introduces four treatments to provide information to pedestrians and cyclists to reduce traveler stress and uncertainty (e.g., pedestrian countdowns, call indicators).
- Address needs for multi–stage crossings: Introduces three treatments for reducing delay and improving safety at multistage crossings (e.g., left-turn overlap for pedestrian half-crossings).
Integrating Pedestrians and Cyclists into Traffic Signals Should Be a Priority, Not an Afterthought
Increasing awareness and providing resources to change the status quo is a step in the right direction in making walking and bicycling safer and more convenient. This helps us achieve improved accessibility, walkability, and healthy communities by improving the built environment. Safer facilities for walking and biking also invite opportunities for improved physical fitness and mental health, and a healthier environment by reducing energy consumption and pollution emissions.
While there has been a general motivation by agencies to design safe and convenient facilities to encourage walking or bicycling, often these designs only include segment-level improvements for pedestrians and cyclists and fail to address their needs at signalized intersections, creating risky or inconvenient crossings. To overcome these challenges and create an accessible and safe environment for everyone, pedestrians and cyclists should be integrated into the signal design and timing optimization process rather than being an afterthought. As transportation professionals, to ensure signalized intersections are not barriers for pedestrians and cyclists, we need to consider pedestrian delay along with vehicle delay and incorporate safety needs that go beyond meeting minimum standards.