About 80% of vehicle/pedestrian collisions occur while the pedestrian is crossing the street. The viability of walking and transit as transportation alternatives depends on the comfort and convenience of crossing arterial and collector roads, since such roads usually accompany important destinations. Areas of dense retail and commercial development or mixes of land uses such as activity centers require frequent locations for pedestrians to cross between a variety of trip endpoints.
The following is a list of safety factors that affect street crossings:
1. Vehicle Speed
Newton's laws dictate that a doubling in vehicle speed results in a stopping distance four times as long and four times as much kinetic energy absorbed during an impact. Driver response times further increase stopping distances, which compounds the safety consequences of high vehicle speeds. "Travelling at 40 mph, the average driver who sights a pedestrian in the road 100 feet ahead will still be travelling 38 mph on impact: driving at 25 mph, the driver will have stopped before the pedestrian is struck." -Patrick Siegman of Siegman & Associates, Palo Alto, CA in the Embarcadero Road Traffic Calming Project, Preliminary Report. When traveling at higher speeds, drivers are also less likely to yield to pedestrians in the crosswalk when the pedestrian has the legal right of way. Drivers operating at high speeds are more likely to exploit the pedestrianís perception of danger in order to discourage pedestrian crossings that would require drivers to slow down or stop.
Numerous pedestrian safety studies have correlated a reduction in speed limits with a reduction in pedestrian accidents and deaths. In order to create safe conditions for pedestrians, the Town of Cary should consider limiting vehicle speeds to 35 miles per hour in built-up areas such as activity centers (as recommended by the Cary Land Use Plan) and locations serviced by transit. In areas of very high pedestrian activity, speed limits of 25 miles per hour may be preferred. Traffic calming devices such as roundabouts, rumble strips, and raised crosswalks may also be considered where reduced traffic speeds are desired.
2. Crossing Distance
Longer crossing distances increase the pedestrianís time of exposure to collision hazards. Multi-lane roads also increase the risk of "multiple-threat" collisions. A multiple-threat collision occurs when one or more vehicles yield to a pedestrian in the crosswalk and block the view of the pedestrian from drivers in other lanes, who pass the stopped traffic and hit the pedestrian at high speed. Long crossing distances also make it more difficult for seniors and persons with disabilities to cross. The challenges of providing safe crossing facilities on multi-lane roads demand that the town carefully consider the impact that road widening projects may have on walkability in populated areas.
3. Pedestrian Sight Distance
In order for a pedestrian to make safe decisions about when to cross a street (without depending on motorists to slow down or stop) it is important for the pedestrian to be able to see far enough in each direction so that he or she can complete crossing before vehicles arrive from beyond view. On wide roads, this becomes a problem. The time required to cross at a walking speed of 4 feet per second (over 15 seconds for a five-lane road) is often longer than the time required for vehicles to arrive from beyond sight distance. A formula for minimum pedestrian sight distance for a given road width may be expressed as follows:
Pedestrian Sight Distance > (Expected Vehicle Speed)*(Road Width)/(Walking Speed)
Or, for a given sight distance, the maximum distance that the pedestrian should have to cross between safe refuge points is
Crossing Distance < (Sight Distance)*(Walking Speed)/(Expected Vehicle Speed)
4. Raised Center Medians and Refuge Islands
Raised center medians featuring pedestrian refuge islands provide shorter crossing distances and increase the convenience of street crossings at areas without crosswalks. By only requiring the pedestrian to cross half of the street at a time, refuge islands allow the pedestrian to exploit shorter gaps in the vehicle traffic on each side - without the risk of becoming stranded in a travel lane. Note that it is important that the median be wide enough to accommodate a person comfortably, and that specially designated refuge points have surfaces that are accessible to all users. Uninterrupted lines of shrubs or other plantings should be avoided.
5. Curb Radii at Intersections
Wide curb return radii at intersections (frequently exceeding 40 feet in Cary) allow motorists to make right turns at high speed, often while failing to stop or even slow down for red lights or pedestrians who have the right-of-way. Wide turn radii also increase the distance that pedestrians must cross at the mouth of intersections. But in areas where marked crosswalks are located farther back, where the distance is shorter, motorists frequently pass or block the crosswalk while preparing to turn right. Turn radii smaller that 20 feet improve walkability by reducing motorist speed at right turns, increasing motorist compliance with signals and pedestrian right-of-way laws, reducing crossing distance, and providing better alignment between the crosswalk and the sidewalk. In older urban areas frequently described as pedestrian-friendly, street corners often have a radius of less than ten feet.
The primary disadvantages of tighter curb radii are slightly increased travel times for motorists (due to slower speeds at intersections) and increased maintenance cost due to wear and tear from tractor-trailers. These disadvantages need to be weighed against the pedestrian safety benefits of tighter radii on a case-by-case basis. Note that on a highly connected grid of streets, the impact of reduced turn radii on motorists is minimized because fewer turns are required per trip.
6. Crosswalk Markings
The safety benefits of crosswalk markings have been the subject of some debate in the traffic engineering profession. In general, well-marked crosswalks (especially zebra-striped markings) increase driver awareness of pedestrians and increase the likelihood that drivers will yield right-of-way. Crosswalk markings can also be used to encourage pedestrians to choose the safest locations to cross, such as at intersections. However, it is believed that crosswalk markings can also give pedestrians an increased sense of security and reduced level of attention that may result in more collisions between pedestrians and those motorists who do not yield the right-of-way. Another explanation that has been given for the correlation between crosswalk markings and increased pedestrian accidents is that markings concentrate crossing activity at those locations by more vulnerable pedestrian groups.
On wide, high-speed multi-lane streets where no signalized protection exists, marked mid-block crosswalks are generally unsafe. (See the recent report by the UNC Highway Safety Research Center at http://www.hsrc.unc.edu/pubinfo/publicinfo.htm .) The combination of (1) drivers failing to yield on high-speed roads and (2) increased pedestrian confidence results in more accidents per pedestrian than at similar unmarked crossing points where pedestrians yield to motorists. On narrower and slower roads, or where additional signage, signals, or traffic calming elements augment the facility, marked crosswalks can improve safety over unmarked conditions.
7. Pedestrian Signals
"Walk" and "Donít Walk" signals notify pedestrians of the proper time to begin crossing the street and prohibit pedestrians from starting a trip across when too little time is left in the traffic signal cycle. Without pedestrian signals, a pedestrians may legally enter an intersection on a stale green light, with only a few seconds left before opposing vehicle traffic starts to move. This is especially dangerous on wide, multi-lane roads. Pedestrian-activated signals also ensure that the signal length is long enough for the pedestrian to cross; otherwise, vehicle-activated signals will often use much shorter signal times for cross-traffic in order to minimize traffic delay. Pedestrian signals should be installed on all intersections that are too wide to completely cross within the duration of the yellow traffic signal and at mid-block crosswalks on wide roads. Note that proper use of pedestrian signals requires that people understand what they mean and how to use them Ė an understanding that is not as widespread as it should be.