Safe Streets, Livable Streets
[B' Spokes: When I read this I could not help but think of conversations from the state around wanting to put rumble strips everywhere. We are designing streets that encourage overrun by motor vehicles and then try to do something else that has little to no effect on the subject or worse discourages biking and walking.
I will also note that while accommodating fast travel by motor vehicle has it's place, but that place is NOT on every single street.]
by Eric Dumbaugh
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In this study, I examine the subject of livable streetscape treatments and find compelling evidence that suggests they may actually enhance the safety of urban roadways. Concerns about their safety effects do not appear to be founded on empirical observations of crash performance, but instead on a design philosophy that discounts the important relationship between driver behavior and safety. This study traces the origin and evolution of this philosophy, and proposes an alternative that may better account for the dynamic relationships between road design, driver behavior, and transportation safety.
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Beyond simply acting as thoroughfares for motor vehicles, urban streets often double as public spaces. Urban streets are places where people walk, shop, meet, and generally engage in the diverse array of social and recreational activities that, for many, are what makes urban living enjoyable. And beyond even these quality-of-life benefits, pedestrian-friendly urban streets have been increasingly linked to a host of highly desirable social outcomes, including economic growth and innovation, improvements in air quality, and increased physical fitness and health, to name only a few. For these reasons, many groups and individuals encourage the design of “livable” streets, or streets that seek to better integrate the needs of pedestrians and local developmental objectives into a roadway’s design.
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Interestingly, clear zones are not the only design feature for which such safety anomalies appear. Hauer reexamined the literature on lane widths and found that there was little evidence to support the assertion that widening lanes beyond 11 feet enhances safety. Instead, the literature has almost uniformly reported that the safety benefit of widening lanes stops once lanes reach a width of roughly 11 feet, with crash frequencies increasing as lanes approach and exceed the more common 12-foot standard.
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Thus, a key question emerges: why does contemporary design guidance recommend practices that the best available evidence suggests may have an ambiguous or even neggative impact on safety, and paradoxically, to do so under the auspices that they constitute a safety enhancement?
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One of the key problems identified by the AASHO committee was the large number of fatalities associated with single-vehicle, run-off-roadway crashes. To address this issue, they heard testimony from Stonex, a General Motors employee responsible for designing the “Proving Ground,” an experimental “crashproof” highway that had 100-foot clearances on either side of the travelway. Based on the test performance of the Proving Ground, Stonex was of the opinion that “What we must do is to operate the 90% or more of our surface streets just as we do our freeways . . . [converting] the surface highway and street network to freeway and Proving Ground road and roadside conditions”
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As shown in Table 3, the livable section is safer in all respects. By any meaningful safety benchmark—total midblock crashes, injuries, or fatalities—there can be little doubt that the livable section is the safer roadway.
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Pedestrian and bicyclist injuries were likewise higher on the comparison section (see Table 4), which may be partly attributable to the fact that the livable section provides parked cars and fixed objects to buffer pedestrians from oncoming traffic. But do the benefits in pedestrian safety outweigh the hazards these features may pose to errant motorists?
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While these results seem to contradict conventional design practice, they confirm a trend that many researchers and practicing engineers have observed for some time, but which has received little substantive elaboration: specifically, that clear zones and other forgiving design practices often have an ambiguous relationship to safety in urban environments, and may be associated with declines in safety performance. The best possible explanation for the enhanced safety performance of the livable sections considered in this study is that drivers are “reading” the potential hazards of the road environment and adjusting their behavior in response.
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The reason why this subject has not received greater attention in design literature and guidance appears to be that it contradicts the prevailing paradigm of what constitutes safe roadway design. Nevertheless, a behavior-based understanding of safety performance is supported by research and literature in the field of psychology, which has focused on the subject of traffic safety as a means for understanding how individuals adapt their behavior to perceived risks and hazards.
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The presence of features such as wider lanes and clear zones would appear to reduce the driver’s perception of risk, giving them an increased but false sense of security, and thereby encouraging them to engage in behaviors that increase their likelihood of being involved in a crash event. If so, this explains why the livable streetscape treatments examined in this study resulted in not only fewer fixed-object crashes, but fewer multiple vehicle and pedestrian crashes as well. ... From the perspective of risk homeostasis theory, the use of high design values is not “forgiving,” but is instead “permissive."
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The passive approach promotes designs intended to support high-speed operating behavior, and then attempts to mitigate a roadway’s hazards through the use of signs and pavement markings. The problem that emerges, however, is that signs and roadways are often communicating contradictory information. The result is that the majority of drivers in urban areas disregard posted speed limits, and seem to learn to disregard road signs altogether, even when they display information that is essential to their safety. ... This latter finding suggests that even conscientious drivers may be unable to comply with posted speed limits when roadways are designed for higher-speed operation.
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I have argued that many of the safety concerns that emerge on urban streets result from design practices that fail to link a roadway’s design to its environmental context, thereby providing motorists in urban environments with a false sense of security and increasing their potential exposure to crashes and injuries. I have further provided a theoretical framework that better accounts for the safety anomalies one observes when examining the literature and data on the crash performance of urban roadways. Yet theory is only the first step. There is a clear and demonstrated need to better develop our professional understanding of the relationship between driver behavior and transportation safety, as well as to enhance our overall approach to the design of urban roadways. This study thus concludes with the hope that by better understanding the relationship between design, driver behavior, and safety, we can design roadways that are not only safe, but also livable.
http://www.naturewithin.info/Roadside/TransSafety_JAPA.pdf
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