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Safety in Numbers
Safety in Numbers

In 1966 federal legislation passed that required automakers to include seat belts in all automobiles sold in the U.S. A quarter century later, a similar bill mandating airbags became law. In both cases, overwhelming evidence indicating these measures saved lives and reduced injuries prompted government action.

As with seat belts and airbags, we know measures such as speed limits, prohibitions against driving under the influence, controlled intersections, highway construction standards and bike lanes reduce collision rates, fatalities, and injuries because decades of research has produced an abundance of data that reveal the case to be true.

Well, not exactly in every case, says Dr. Krista Nordback.

Dr. Nordback is a transportation engineer and research associate in PSU’s Transportation Research and Education Center (TREC). She studies bicycle and pedestrian infrastructure: its use and efficacy, and the collection and analysis of cyclist and pedestrian count data. She also has expert knowledge of methods for estimating miles traveled and the relationships between vehicle traffic, pedestrian and cyclist volume and collisions.

According to Dr. Nordback, the tools researchers, planners, and transportation engineers have to evaluate the impact of bicycle infrastructure on crash rates are formulated using imprecise estimates of the number cyclists on the road. That’s a problem because without precise data, it’s very difficult to prove treatments such as bike lanes actually reduce collisions, injuries, and fatalities.

With currently available resources, it is possible to predict the cause and number of vehicle collisions to be expected at a given point on a road with a fair degree of accuracy. It is also possible to estimate how treatments such as road signs, speed limits, and turn lanes will improve safety by reducing vehicle crash rates. Planners, engineers, transportation officials and researchers can make these predictions thanks to a cache of scientifically proven tools, published datasets and methods for safety analysis compiled in the Highway Safety Manual (HSM).

Unfortunately, similar tools for predicting bicycle crash rates and evaluating safety-enhancing countermeasures were not developed with the same data-driven rigor as those for vehicles. The reason, according to the Federal Highway Administration, is that there isn’t enough “good, quality information” on cycling mode share to develop mathematically sound functions capable of producing accurate predictions.

“The tools in the HSM work because of the quantity and quality of vehicle count data used to develop them,” Dr. Nordback said. “We just don’t have that kind of data when it comes to bicycle volumes and that’s a problem. If we don’t know how many people are using facilities like bike boxes and cycle tracks, how are we supposed to know if the infrastructure is making riding safer?”

Improving volumetric data collection and analysis is a theme of much of Dr. Nordback’s research. In Minnesota, Colorado, and Oregon, she examined the states’ counting activities and methods of data analysis in order to frame the state of the art in non-motorized traffic monitoring programs. In Washington she worked with the state’s Department of Transportation developing facility-level methods to estimate annual pedestrian and bicycle miles traveled using data collected from over thirty cities.

In Boulder, Colorado, Dr. Nordback and colleagues evaluated counting methods and analyzed datasets determining best practices for producing the most accurate estimation of annual average daily bicyclists (AADB)—the annualized average twenty-four-hour volume of bicycles at a given location—a critical metric for the evaluation of safety enhancing measures. And by creating bicycle safety performance functions (equations that predict the average number of crashes per year) for the City of Boulder, she showed that given adequate count data equations could be developed on a city-by-city basis.

In Oregon, Dr. Nordback and fellow TREC researchers partnered with the Oregon Department of Transportation to evaluate the accuracy of pneumatic tubes used to count vehicles, bicycles, and pedestrians. The research team’s findings indicate that the technology can produce data with a less than ten percent error rate. Improper deployment of the tubes, however, could result in undercounts with error rates as high as seventy percent. That’s a gap substantial enough to impact a transportation agency’s ability to assess demand for bicycle infrastructure, evaluate safety performance, or obtain federal and state funding for infrastructure projects.

Though accurate estimates of cyclists on the roadway are an essential metric for evaluating the safety impact of bicycle infrastructure, cities that count riders frequently use a variety of methods, some more precise than others, which make it difficult to determine AADB. Portland, for instance, has a number of continuous counting devices located on the Hawthorne Bridge, Tilikum Crossing, the Eastbank Esplanade, and elsewhere. These devices collect data twenty-four hours a day, seven days a week, year round. Pneumatic tubes placed across roadways around town collect data in durations ranging from several days to a few weeks at each location they’re placed. Much of the city’s bike ridership data, however, comes from an annual two-hour count conducted by volunteers. During the last count from which data is publicly available (2014), more than 100 people volunteered at 218 locations citywide and counted 41,590 cyclists. 

“Lots of cities count cyclists this way,” Dr. Nordback said, “and they use the data they collect to evaluate bicycle safety. But they’re taking these two-hour counts and using them instead of AADB. That is why we don’t have a good sense of how many riders are using the system—a two-hour count at specific locations doesn’t necessarily reflect how many people might be riding at that same location in a week, in three months, or during different seasons. And cities often don’t share and pool the data they collect. And without a large source of data from all over the country, it’s impossible to create universal safety performance functions like those for vehicles in the HSM.”

While organizations like the National Bicycle and Pedestrian Documentation Project (NBPD) do offer transportation agencies guidelines for data collection and repositories to compile data in, they do not aggregate and curate count data into a database available to transportation professionals, planners, policy makers and researchers. To provide such a service, Dr. Nordback and her TREC colleagues partnered with organizations (including the NBPD) and cities across Oregon and the country to create the Bike-Ped Portal, a national archive for bicycle and pedestrian count data. The Bike-Ped Portal gives researchers, local agencies, policymakers, and transportation professionals the resources to turn their count data into knowledge and action.

“I entered this field because I wanted to know if the infrastructure we’re building actually enhanced safety,” Dr. Nordback said. “To answer that question I need to know how many people are using the system, and right now I don’t have that information. But there’s an explosion in bicycle and pedestrian counting going on across the nation, and as more cities sign on to use the Bike-Ped Portal and add their data, we’ll be able to leverage that information to improve bicycle crash prediction, which will be a huge step forward in our ability to enhance safety conditions on the road.”

We may be a long way from having enough evidence on the impacts of bicycle and pedestrian infrastructure to spur local, state, or federal action mandating safety enhancing measures. But as ridership in cities around the country has increased over the last decade and municipalities are encouraging residents to choose more active modes of transportation as a means to reduce single occupancy vehicle travel, investments in bicycle infrastructure and counting technologies has gone up as well. For Dr. Nordback and other transportation engineers, the renewed interest in cycling provides opportunities to close knowledge gaps and more accurately evaluate cyclist and pedestrian use of roadway systems and facilities. In time, the “explosion” of data researchers at PSU are funneling into the Bike-Ped Portal will lay the groundwork for a better understanding of what types of infrastructure save lives and reduce injuries among the population of cyclists and pedestrians sharing the roads with vehicles and their drivers.