Arguably, one of the most important factors effecting pedestrian mobility is the perception of a safe environment.
To create a safe environment, a number of factors must be adequately addressed:
the speed of vehicular traffic in the travel lane alongside the pedestrian’s route (for example, alongside the sidewalk);
the degree of separation between the sidewalk/pedestrian facility and the adjacent travel lane;
the ease and ability to cross the street and intersecting streets at the end of the block; and,
the development pattern surrounding the street -- promoting a high degree of visibility of streetlife from adjacent buildings and that contributes a high volume of pedestrian usage.
Exposure of pedestrians to high speed traffic is perceived as unsafe by pedestrians and is a strong deterrence to pedestrian use. Most streets have been designed to vehicular travel at a specific speed, referred to as the street’s design speed.
Figure 9. Wide lanes and fast traffic? Very dangerous. The graph above illustrates the effect of vehicle speed impact on survivability in vehicle-pedestrian crashes. Crashes where pedestrians were impacted by vehicles traveling at 20 mph were fatal to 5% of pedestrians, whereas, 85% of pedestrians struck by a vehicle traveling at 40 mph died. (Image credit:
Hall Planning & Engineering, Inc.)
Standard practice for the most recent 60+ years has been to overdesign streets, so that they can accommodate higher speed vehicular travel than necessary for their assigned function. This practice often results in streets that allow for vehicular travel that is perceived as too fast for pedestrian usage. The picture below helps illustrate the differences between design speed, operating speed, the speed that vehicular are actually traveling, and the posted speed limit, and the lack of correlation between these
“speeds.” The term inferred speed, as referred to in Figure 10, is the speed that the street design conveys to the driver is the appropriate speed to be traveling.
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Figure 10. Posted speed limit is not the same as design speed!
Keeping vehicular speed slow in the travel lanes adjacent to the sidewalk or pedestrian facility is one of the most effective strategies to create a safe environment for pedestrians. Keeping streets and travel lanes narrow has the effect of moderating vehicular traffic speed and is one the most effective and least expensive tactics that can be used for that purpose. Appropriate street width to promote pedestrian mobility depends upon a number of factors and must also consider the other functions that the street is required to perform. Ideally, the width of the travel lanes in a street should be as narrow as possible without compromising other required street functions, such as emergency service vehicle access;
typically, this corresponds to a minimum width of 10 feet for travel lanes. Conversely, excessively-wide travel lanes and street sections encourage higher speed vehicular traffic, creating an unsafe environment for pedestrians and adversely impacting pedestrian mobility.
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Avoid Over-Design!
Streets must be properly designed to facilitate pedestrian mobility in the community. In his post, Walkable streets: Considering Common Issues., (Blog post featured on Better! Cities & Towns, March 11, 2013 ), Geoff Dyer points out that to create a safer environment for pedestrians slower vehicular movement should be encouraged through careful street design, where the pavement widths of walkable streets are narrower than those of conventional streets. Dyer notes most conventional streets are typically designed for a higher “design speed” than the intended “posted speed.” This practice results in streets with excessive pavement width which encourages vehicles to drive in excess of the posted speed as well as the design speed. In response Dyer recommends that the design speed be the same as the desired posted speed.
Expounding on this concept, Dyer points out that in an urban context, to move traffic along, streets don’t actually need to operate at higher speeds, and thus don’t require wider lanes. Research has shown that streets with traffic flowing at 25mph have the greatest capacity for vehicles per lane. This also improves both pedestrian safety and the perception of pedestrian safety -- the difference between being struck by an automobile traveling 25mph and 45mph is often the difference between a survivable pedestrian injury and a fatality. Designing a street system based on slower speeds also makes it easier to enhance pedestrian mobility through better street geometries allowing for smaller (tighter) turning radii and a more connected block structure.
Figure 11. Typical roadway capacities are greatest with operating speeds near 25 mph. Image credit: Geoff Dyer;
from the Highway Capacity Manual, Transportation Research Board.
Examining the design and land development factors associated with crashes involving pedestrians, cyclists, and motorists in urban environments. Eric Dumbaugh and his associates examined design and land development factors and their association with automobile crashes involving pedestrians, cyclists, and other motorists. Their research found that the presence of pedestrian-scaled retail uses along roadway corridors was associated with statistically significant reductions in the incidence of multiple-vehicle, fixed-object, and pedestrian crashes. Dumbaugh and his associates reported that this is almost
“The masters of space and time awaken to find themselves slaves of distance and haste”
-- Wolfgang Sachs, For Love of the Automobile (1992)
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certainly attributable to the effects of the pedestrian-scaled commercial and retail uses on vehicle speeds, noting that street-oriented buildings create a sense of visual enclosure to the street, communicating to the driver that greater caution is warranted, resulting in reductions in both vehicle speeds and crash incidence (Dumbaugh, 2006; Ossenbruggen, Pendharkar, & Ivan, 2001; Smith & Appleyard, 1981).
In their research, Dumbaugh and associates cited a recent study that compared roadway segments with identical street design geometries but different roadside characteristics. This study found that the presence of urban roadside features, such as buildings located adjacent to the street and sidewalks, were associated with speed reductions of up to 10mph (Ivan, Garrick, & Hanson, 2009). This report by Dumbaugh and his associates is available at: http://swutc.tamu.edu/publications/technicalreports/161107-1.pdf [E.W. Dumbaugh, W. Li, K. Joh, Examining the Design and Developmental Factors Associated with Crashes Involving Pedestrians, Cyclists, and Motorists in Urban Environments, May 2012, Texas A & M University Transportation Institute Technical Report]
Fundamental Driver - Pedestrian Interaction Considerations:
1) Visibility is required to facilitate safe driver response and pedestrian reaction.
2) Drivers making critical movements – i.e., turning, are focused on potential on-coming traffic ahead of them and traffic signals and less aware of pedestrians that may be crossing perpendicular to their right or left. This is one factor that adds to the difficulty for pedestrians to cross at corners.
3) The longer the arc of that the turning vehicle makes, the greater the distance the automobile travels and builds up speed before the driver sees the pedestrian and reacts; the higher the speed, the greater the breaking distance.
4) The wider the street is at the pedestrian crossing (the longer the crossing span) and therefore, the greater the pedestrian exposure.
5) Darkness and inclement weather also reduce visibility for both pedestrians and drivers.
6) Distracted drivers are less apt to see a pedestrian and therefore less apt to react in a timely manner; distraction can be caused be factors internal to the automobile, such as cell phones, conversations, or external, such visual clutter along the roadside and confusing or complex signage and roadway configurations.
7) Drivers entering or exiting driveways along the street often pose challenges to pedestrian safety and mobility, particularly drivers turning left into a driveway, across from and ahead of traffic, as rush to beat on-coming traffic without looking left to see if pedestrians are crossing the driveway on the sidewalk along the street.
8) Drivers exiting a parking structure can sometimes have difficulty seeing the pedestrians walking along the sidewalk in front of and parallel to the parking structure, depending on the design of the parking structure; the converse is also true – depending on the design of the parking structure, pedestrians may have difficulty seeing exiting vehicles.
The Federal Highway Administration provides a Toolbox of Countermeasures that can be used to respond to most of these issues: http://safety.fhwa.dot.gov/ped_bike/tools_solve/ped_tctpepc/
A New York City Pedestrian Safety Study examined crashes in which pedestrians were injured or killed and found that about half of pedestrians hit were crossing at crosswalks with signals, and more than half of those were obeying the signal.
Most of those killed while obeying walk signals were hit by turning vehicles
– Sam Schwartz, former NYC Traffic Commissioner in The Savvy New Yorker’s Guide to Jaywalking, Adam Martin, New York (Magazine), January 31, 2014
http://www.nyc.gov/html/dot/downloads/pdf/nyc_ped_safety_study_action_plan_technical_supplement.pdf
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How drivers and pedestrians perceive the world
The relationship between motorized vehicular travelers and pedestrians is a significant consideration as typically pedestrians and drivers utilize the same street network, either traveling along or across the same streets.
In one regard, both motorists and pedestrians share a similar concern, typically reflected in their actions, that a crash with a motorized vehicle could have dire consequences and must be avoided. Crashes or collisions cause damage by the result of the force exerted on the colliding objects. Force = mass x acceleration. For a pedestrian in a collision with a vehicle, acceleration does not mean necessarily mean the rate of acceleration of the vehicle, which is often decreasing during breaking, but the rate of
acceleration for the pedestrian. As an example, a pedestrian standing still hit by a car moving 25 mph will suddenly accelerate by approximately 25 mph; if the car weighs, for example, 1 1/2 tons, the force exerted by the impact on the pedestrian is 37.5 ton miles per hour -- to a much lesser extent, the pedestrian’s weight counters the force exerted by the vehicle -- for example, the force exerted upon the vehicle in this crash by a 100 pound child would be 1.25 ton mph, so that the total impact of force in this collision would be 36.25 ton mph). Widely publicized vehicular crash tests reveal that many vehicles are now designed and constructed to withstand simulated 5 mph bumper-to-bumper crashes with little or no resulting damage but fare much less well in simulated higher speed crashes (e.g., @ 25 mph) with other vehicles. In these crash test, the vehicles incorporate a number of features including construction designed to dissipate some of the force that would otherwise be exerted on whatever they collide with, and also provide a variety of safety and restraint systems for the passengers. Of course, pedestrians do not have any of these features, so when they are hit by a vehicle, they experience the full brunt of the force exerted.
In addition to being particularly concerned avoiding colliding with other vehicles, motorists are also concerned with their destination. They don’t want to miss: their turn; their exit; the green light; the correct lane, and their destination. The number of critical movements, terminology for the possible number of turning and lane shifting options that can occur at specified points along the street system, significantly complicates these objectives for drivers. The greater the number of critical movements at an intersection, for example, the more items that the driver must look at and react to. Accordingly, drivers are often much less aware of bicyclists and pedestrians in their environment, and as a result, bicyclists and pedestrians are more likely to be struck by a motorist that did not notice them until too late stop in time.
Basically, both drivers and pedestrians relate to other objects in their trajectory in the following manner:
Look - Perceive - Understand - React. Omission of or interference with any of these steps can be deadly, particularly with higher speed motor vehicles are involved.
This snapshot ignores distracted and impaired drivers and pedestrians who present a significantly greater danger to both themselves and others.
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