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Safe Crossing
Safe Crossing

“It’s like an airplane falling out of the sky every other day.”

Such was Scott Bicker’s assessment of the 4,500 pedestrians killed on American streets every year. Bicker, the executive director of America Walks, was quoted in an article about the multi-national initiative to end roadway causalties called Vision Zero.

Last year, Portland joined fifteen U.S. cities that have embraced Vision Zero and dedicated resources to ending roadway fatalities and injuries within city limits. The Vision Zero Crash Map developed by the Portland Bureau of Transportation (PBOT) is one of the products of the city’s investment. The map tracks traffic-related instances of serious injuries and deaths on Portland streets.

Although the map shows the number of pedestrian injuries pales in comparison with those of drivers and passengers of motor vehicles, the data reveals high pedestrian mortality rates. The reason: pedestrians, like cyclists, are more exposed and therefore more vulnerable to injury or death than a vehicle’s occupants. So given the vulnerability of pedestrians walking the streets, what can Portland and other cities do to reduce collisions and and save lives?

Just up the road from PBOT’s Southwest 4th Avenue offices, in the Maseeh College of Engineering and Computer Science, Dr. Sirisha Kothuri, a post-doctoral research associate, is working to increase the efficiency of signalized crosswalks, a project that may also help cities reduce deaths and injuries resulting from pedestrian/vehicle collisions.

An affiliate of PSU’s Transportation Research and Education Center (TREC), Dr. Kothuri studies traffic operations and develops technologies to improve the experience of walking and cycling for pedestrians and cyclists using street networks. Specifically, her work aims to enhance the efficiency, safety and walkability of signalized intersections where motor vehicles have traditionally been prioritized.

Working with collaborators at Northern Arizona University, PBOT, and transportation agencies in the cities of Mesa and Flagstaff, Arizona, Dr. Kothuri and her fellow investigators are evaluating pedestrian crossing schemes at signalized intersections to try to understand how they might impact delays. Most pedestrian fatalities and serious injuries occur between 6 p.m. and 6 a.m. and many occur at intersections. One of the factors frequently involved in these incidents is pedestrian behavior: jaywalking, perception of risk, perception and speed of crossing devices, herd mentality, and so on. Dr. Kothuri and her colleagues think it’s possible to change risky behaviors at crosswalks, increase compliance with traffic signals, and improve safety by shifting the prioritization of signals from vehicle to pedestrian traffic, thereby reducing pedestrian delays.

“Transportation agencies try to emphasize the prioritization of pedestrians at signalized intersections,” Dr. Kothuri said. “And given their vulnerability, pedestrians should be accorded the highest priority, but in practice that doesn’t always happen.”

In order to test the hypothesis that prioritizing pedestrian crossing at signalized intersections could increase safety by reducing risky behaviors, Dr. Kothuri modeled several pedestrian crossing schemes on a simulation of a busy stretch of Portland’s Southeast Division Street between 119th and 130th Avenues. Not surprisingly, she found that when traffic volumes were high and pedestrian volumes low, prioritizing vehicles to reduce overall delay is a best practice. The simulations, however, did suggest that during off-peak periods, the signals could prioritize pedestrians without adversely affecting traffic, which could reduce instances of jaywalking and other risky behaviors.

“Peaks in pedestrian volume are different from those in vehicle volume,” Dr. Kothuri said. “So during the lunch hour, for example, when people are out walking to restaurants, parks, or running errands, and there are fewer cars on the road, we could switch the timing of signals so people aren’t waiting as long to cross the street.”

To move this idea out of the digital world of computer modeling and test it on actual city streets, the research team developed an algorithm that prioritizes pedestrian crossing when traffic volumes are low and is deployable in signal control software already in use. In partnership with PBOT, the research team is testing the algorithm at the intersection of SE 122nd and Division in Portland and on the streets of Mesa and Flagstaff in Arizona. And because pedestrian prioritization is appropriate for some but not all intersections, Dr. Kothuri is developing a user manual that will help transportation agencies identify places where they can implement the augmented signal scheme.

“It’s a fine balance, trying to reduce delays for everyone,” Dr. Kothuri said. “It’s an art, really, and it’s hard. Traffic engineers are up against difficult circumstances in their efforts to manage demand from everyone using the system. But we think the work we’re doing here can help cities move everyone around more equitably and efficiently and maybe even decrease instances of pedestrian/vehicle accidents at some intersections by eliminating long waits that contribute to risky behavior when traffic volumes are low.”