into how streets and buildings shape driver and pedestrian interactions
aren't the sole cause of safer walking environments, according to two new
studies, including one conducted by researchers at UC Berkeley's Traffic
Safety Center. New evidence suggests that the more people walk, the safer
Center's study (see sidebar), along with an earlier one conducted by Peter
Jacobsen in 2003(1), give strong evidence that the traditional method
of ranking the dangerousness of an intersection according to the number
of pedestrian-vehicle crashes that
occurred there over a period of time has given an inaccurate picture of
the actual threat posed to pedestrians at those intersections. By also
taking pedestrian volumes into account—the number of pedestrians that
use an intersection over a period of
time—both Jacobsen and the Center researchers found that, surprisingly,
the "risk" that any one pedestrian might be hit by a motor vehicle
is often lower at intersections with greater pedestrian volumes—even if
those intersections experience more collisions.
For the TSC project,
Center researcher Noah Radfordused Space Syntax, a suite of
modeling tools and simulation techniques
developed by the University College of London, to estimate pedestrian
volumes in the city of Oakland, CA.
In their report, "Space
Syntax: An Innovative Pedestrian Volume Modeling Tool for Pedestrian
Safety," Raford and Center Director David Ragland describe how pedestrian
volume estimates generated by the Space Syntax model were used to
calculate exposure, or the rate of pedestrian contact with potentially
harmful situations involving motor vehicles, and risk, or the probability
that a pedestrian-vehicle collision would occur.
"The Space Syntax tools
analyzed the layout and connectivity of urban street grids and generated
'movement potentials,' which were then compared to sampled pedestrian
counts at key locations and land-use indicators such as population and
employment density," Raford and Ragland write. "The resulting correlations
were extrapolated to predict pedestrian volumes on a street-by-street
level for an entire city."
Using this method, Raford
and Ragland found that 10 of the city's 12 most dangerous intersections
were clustered in the eastern area of the city, an area with relatively
low pedestrian volumes. Of the intersections surveyed, only one was in the
"This finding suggests
that although the highest volume intersections may be within the downtown
area, these intersections are much safer than those in East Oakland
because they accommodate a greater number of pedestrians with fewer
pedestrian accidents, even though they may have a higher number of
absolute pedestrian crashes."
Raford and Ragland use as
an example two Oakland intersections, one in downtown and one in east
Oakland. The downtown intersection was considered one of the most
dangerous intersections in the downtown area, experiencing "an average of
three pedestrian-vehicle crashes per year." Using Space Syntax, Raford and
Ragland determined the intersection's annual pedestrian volume to be
998,000. The researchers found that these figures can be contrasted to
those for an intersection in East Oakland where the average pedestrian
volume was much lower, 343,000 a year. Pedestrians crossing at this
intersection were approximately 5.6 times more likely to be involved in a
collision than they were at the intersection in downtown. Data from every
intersection studied for this report yielded similar results.
"From a public policy
standpoint, from a safety standpoint, the message is, if you want safer
streets, have more people on them," Raford said.
In his 2003 study, "Safety
in numbers: more walkers and bicyclists, safer walking and biking"(1)
Jacobsen observed a similar phenomenon, but on a much broader level of
analysis. Jacobsen examined the relationship between the rates of pedestrian
and bicycle activity and the number of times pedestrians (or cyclists)
were hit by cars in 68 California cities and multiple European countries
and found that in most cases, the risk of collision went down as pedestrian
and bicycle activity increased. For example, Jacobsen found that the per
capita fatal injury rate for pedestrians and bicyclists in the Netherlands
and the U.S is comparable: about 1.9 per 100, 000, even though the share
of bicycle/pedestrian trips in the Netherlands is much higher, 46 percent
versus 6 percent in the U.S.
Drivers Become More Careful
The results were consistent
across several regions and countries and could not be explained solely
by changes in pedestrian behavior, Jacobsen noted. According to Jacobsen,
it is unlikely that pedestrians obey traffic signals or defer to vehicles
simply because there are more pedestrians around. In fact, common sense
would suggest that the opposite is true—the more pedestrians are around,
the more confident, and less careful, individual walkers and cyclists
become. Rather, Jacobsen sees the results as an expression of the relationship
between motorist behavior and pedestrian activity. In other words, drivers
drive more carefully when they observe large numbers of walkers and bicyclists.
"Adaptation in motorist
behavior seems more plausible [than other alternatives] and other
discussions support that view," Jacobsen writes. "In addition, motorists
in communities or time periods with greater walking and bicycling are
themselves more likely to occasionally walk or bicycle and hence may give
greater consideration to people walking and bicycling."
Further analysis of this
phenomenon may help planners find ways of improving the safety and
walkability of built environments. For instance, if motorists change their
behaviors according to the number of pedestrians on the street, how might
the presence of design elements such as continuous sidewalks, crosswalks,
bike lanes, medians and rows of trees further influence drivers'
conduct? Will the presence of such elements further decrease risk of
pedestrian injury simply because pedestrians walk and bike more in
environments designed to accommodate them? Adding crosswalks, bike lanes
and medians to an existing built environment could make pedestrians safer
not just by virtue of the added safety provided by a crosswalk, but also
because pedestrians are interacting with that environment in greater
"If shown to be true and
to be the result of more careful driver behavior, these findings have very
strong implications for policy," Ragland said. "I think it will become
clear that programs for promoting walking, and maybe biking, may not have
the feared effects of dramatically increasing the number of ped/bike
injuries, but may actually reduce risk for individual peds and bikes."
"We're really at an
amazing stage in research," Raford adds. "The data doesn't say
what gets people out [walking and biking], but it has the potential to
show what types of neighborhoods would be safer."
P. L. Jacobsen "Safety in numbers: more walkers and bicyclists, safer
walking and bicycling" Inj. Prev., Sep. 01, 2003 9: 205-209.