A Call for Proactive Road Design

By Nicholas Ferenchak

Image courtesy NYC DOT

When transportation safety analysts prioritize areas for pedestrian and bicycle safety improvements, they look for evidence of crashes, injuries, or fatalities. In doing so, are they ignoring parts of the built environment that are so unsafe that they are never used by pedestrians and bicyclists, and thus do not generate a crash history?

At the University of Colorado, Professor of Civil Engineering Wesley Marshall and I set out to answer this question by looking specifically at child pedestrian and bicycle trips to school — or lack thereof. Based on survey results from more than 1,300 parents in the city of Denver, Colorado, we were able to pinpoint roads with design characteristics that act as barriers for kids walking and biking to school. Children can avoid some of these barriers by simply taking another route. Other times, the alternative route is further than a child will walk or bike, and the trip is effectively suppressed because of perceived safety concerns. With this information on trip suppression, we were able to create a new tool that can help us proactively prioritize projects based on desire lines. Barriers that suppress walking and biking to school — such as sidewalk gaps or high-speed corridors — populate an interactive map that we hope will be used to broaden and deepen discussion of traffic safety priorities, because there are many places — in Denver and around the country — that are so unsafe, they are invisible in traditional safety analyses.

Examples of these invisible safety issues are found throughout our cities. Survey respondent Lisa Kline told us that she would love to have her son bike the six blocks on Steele Street to his school in Denver. Those six blocks only have sharrows, however, which Ms. Kline doesn’t believe provide a safe refuge from all the traffic that uses the road to get over I-25. “Shouldn’t middle schools and elementary schools have bike lanes connecting them? It’s dangerous and I won’t let my 7th grader ride his bike to school. So, I drive.”

Ms. Kline’s concern with traffic safety — a concern that is surely echoed hundreds of thousands of times over by parents throughout the country — illuminates a fallacy in the reactive way that we currently think about traffic safety. Look at any of Denver’s crash-based traffic safety reports from the last decade and you’ll see that this segment of Steele Street has never been identified as an issue. This is because there were no bicyclist injuries or fatalities — or any bicyclist crashes at all, for that matter — over the last few years. Could it be that there were no crashes precisely because people like Ms. Kline and her son got in a car after they perceived the road as unsafe for cycling? This is a question every traffic engineer needs to begin asking.

According to the Vision Zero Network, the goal of Vision Zero is to “eliminate traffic fatalities and severe injuries, while increasing safe, healthy, equitable mobility for all.” Right now, because of the “zero” in the name, and the visceral relationship we have with injuries and fatalities, the first part of the definition gets most of the attention. However, the latter part is just as important. By focusing on where crashes are occurring, we are currently taking a reactive approach to our traffic safety issues, possibly only accounting for the fearless walkers and bikers who are out there today. If we want to unlock our streets for interested but concerned users — like Ms. Kline and her son — we need to think about safety more proactively by devising a way to prioritize roads such as Steele Street, before the worst occurs.

Professor Marshall and I are currently working with Denver Public Schools, and officials with the city and county of Denver, to do just that. Our proactive safety initiative accounts for neglected traffic safety issues by measuring the number of trips suppressed because of safety concerns. If we can identify a road where numerous trips are being suppressed because of these concerns, we can say that something is wrong in terms of safety, even if currently there is no crash history on the road. Recent research shows that these types of facilities that suppress trips are endemic to our cities.

To quantify the number of trips that are being suppressed because of safety concerns, the survey we administered to parents in Denver asked which roadway characteristics would cause them to allow or disallow their children to walk or bike to and from school. Each parent was provided pictures from several roadway scenarios throughout Denver that included various design characteristics previously identified as important factors to parents in Safe Routes to School surveys. Characteristics included the number of travel lanes, presence of sidewalks and bike lanes, vehicle volumes, and vehicle speeds. The presence of sidewalks was the most important factor in the decision to walk, followed by vehicle volumes. For bicycling, vehicle volumes were the most important determinant, followed by the presence of bike lanes. With these results, we were able to derive the rate of disallowance — what we called our suppression rates — for every roadway in Denver, as well as identify specific traffic safety barriers.

However, just because a road is perceived as unsafe doesn’t mean that it should be prioritized. What if there is an unsafe road in the middle of nowhere with few possible users? Prioritization must be a combination of safety perceptions and user demand.

To account for user demand in our model, we first estimated the location of children who would be possible pedestrians and bicyclists. We considered children within half a mile of their closest school as possible pedestrians, and children within one mile of their closest school as possible bicyclists. We then entered traffic safety barriers — as defined by parents in the survey — into our model and determined how far children must walk or bike to avoid those barriers. If the distance a child had to travel to get to school while avoiding those barriers increased beyond the distance they were willing to walk or bike, we considered their trip to be suppressed.

The final element of the tool we developed is an interactive map that defines where trips are being suppressed because of safety concerns — regardless of crash history — and which barriers are responsible for that suppression. With this map, traffic safety professionals can, for the first time ever, take a proactive approach to traffic safety. Roads can be made safer for those currently walking and biking while also opening our streets to those who are interested but concerned.

Evidence shows that, at least for children walking and biking to school, the majority of our traffic safety issues are neglected by solely focusing on where crashes are occurring. As traffic safety practitioners, advocates, and researchers, we must end this reactive and myopic approach to traffic safety, whereby injuries and fatalities are the only indicators of built environment problem areas. Instead, we must remember to proactively account for unsafe and unused places so that we can encourage safe, healthy, and equitable mobility for all.

[This article first appeared in Transportation Alternatives’ Vision Zero Cities Journal in 2018.]


Nicholas Ferenchak is an Assistant Professor in the Department of Civil, Construction & Environmental Engineering at the University of New Mexico. His research focuses on active transportation and safety.