Why—and How—Pedestrians and Bicyclists Count

TSC Director David Ragland Explains Key Findings about California's Unique Pedestrian Safety Issues

"Count the pedestrians in the picture in the next 10 seconds," said David Ragland, TSC Director, as the photo (above) of a major Tokyo intersection flashed on the screen in front of an audience of roughly 60 human factors and traffic safety experts and headquarters and district employees from the California Department of Transportation (Caltrans) at the Richmond Field Station late last month.

Ragland was giving his "Pedestrian and Bicycle Safety" presentation at the two-day workshop, which was organized by California Partners for Advanced Transit and Highways (PATH) at the request of Caltrans to introduce the agency's decisionmakers to some of the latest thinking in the discipline of human factors and driver behavior studies. Workshop documents described it as "a first step in putting policy to practice" and "a unique opportunity to hear from distinguished researchers from across the country." The reason for the human factors emphasis is that driver behavior contributes in one degree or another to nearly all traffic crashes (93 percent, according to a national study).

Pedestrian and bicyclist safety (for the purposes of his presentation, Ragland lumped both groups under pedestrian safety) is a key element in any safety plan, but especially for a state agency like Caltrans, when it is looking at driver behavior.

In terms of simple numbers, crashes involving pedestrians tend to be more severe, with 10 times as many fatalities per incident as crashes where all the parties are in a vehicle. The reason: the human body is at an enormous disadvantage in terms of mass when it comes to a motorized vehicle; and motor vehicles give their occupants considerable protection.

"That's the general picture," Ragland said, but the argument is even more compelling for California.

Factors special to the state:

California has a higher percentage of pedestrian fatalities per traffic fatalities overall than the national percentage: between 17.2 percent and 20.2 percent, compared to 11.2 percent to 12.6 percent over four recent years (see slide).

California's State Highway System has a disproportionate share of pedestrian fatalities, compared to its mileage: 23 percent of fatal pedestrian collisions occur on state highways, but they account for only 10 percent of the total mileage (see slide).

These findings argue for more study, especially in situations where state highways are impinging on more populous urban areas, as is the case in a number of California cities. Additionally, a statewide program addressing pedestrian safety could create leverage for local programs and set a standard for local programs to aspire to.

Ragland outlined a few key elements of the research agenda he is proposing.

A "critical issue" is pedestrian exposure, he noted, which gives a stronger sense of the actual, real-world likelihood of pedestrians being hurt or killed because it incorporates the amount of time and distance that people walk. Despite the importance of understanding pedestrian exposure, data about it are far behind comparable information for motorized travel.

"Vehicle volume has lots of complex ways to be measured," he noted, because there is a large incentive to develop them because so much hinges on having the data. Federal funding formulas, engineering designs, and regulations are all keyed to the volume of vehicle travel on a system.

No such rich way of measuring activity exists for pedestrian volume. It needs to be developed as part of a policy addressing pedestrian needs. If such capabilities were developed, it would enable more precise characterization of pedestrian needs, he said. That is why the TSC is working, in partnership with PATH, to evaluate and develop faster, more accurate and more automated methods to measure pedestrian activity.

This is important to know in order to determine risk, which can guide policy decisions and help target resources where they are most needed. Risk is expressed as the probability of collision/injury/fatality per unit of exposure. To calculate risk, there must be a reliable measure of exposure.

It's important to be able to measure exposure and risk, because they often tell different stories. And the more measures that there are, the richer a picture of the pedestrian situation will be (see slide at left).

A key project that Ragland chose to speak about was a database that contains information about all the intersections in the State Highway System. The goal is to take the database, which has been built by TSC researchers, and overlay pedestrian crashes, so that their distribution will be understood. It would be the first such analysis in the country.

As an illustration of the need for more study, he discussed the pedestrian volume crash map analysis of Oakland that the TSC did. Researchers found that, seemingly counter to what would be expected, the rate of pedestrian crashes went down as pedestrian volume increased. This had been reported in earlier studies as well.

The implications are important, Ragland said, because it means that "every time you get 100,000 more pedestrians to walk, the absolute number of crashes does not go up linearly."

Ragland said the reason for this-safety-in-numbers phenomenon is not clear. It could be that drivers are more mindful of pedestrians when they are present in the environment in greater numbers. Ragland speculated that it might be the "birds on the wire" effect, that one or two lookouts among the pedestrians provide signals to the rest of the group that prompt them to choose the safest paths or maneuvers.

Ragland called it a "sacred obligation" of public health professionals to avoid putting people at risk—including in their efforts to have them walk more. "It's no good to improve someone's respiratory function by having them walk or jog, if they end up getting hit by a car," he said. He commended Safe Routes to School as a good model because it incorporates safety into its walking advocacy efforts. But there is a need to do more.

Link to Human Factors Workshop Web page: http://www.techtransfer.berkeley.edu/humanfactors/

Other links:

American Community Survey: http://www.census.gov/acs/www/
Behavioral Risk Factor Surveillance System: http://www.cdc.gov/BRFSS/
National Household Travel Survey: http://nhts.ornl.gov/
California Statewide Travel Survey: http://www.dot.ca.gov/hq/tsip/otfa/mtab/Statewide%20Housewide%20Travel%20Survey.htm