The 2000 Uniform Vehicle Code and Model Traffic Ordinance define a crosswalk as "any portion of a roadway at an intersection or elsewhere distinctly indicated for pedestrian crossing by lines or other markings on the surface."1 Road striping serves to legally establish the crosswalk; alert road users of a pedestrian crossing point across roadways without traffic signals or STOP signs; and provide guidance for pedestrians crossing roadways by defining paths within the signalized intersection, according to the Manual on Uniform Traffic Control Devices (MUTCD).
Many guidelines and recommendations govern the design of new intersections and upgrades to existing intersections that attempt to meet the needs of the entire pedestrian population, which ranges in age, physical and mental capabilities, emotional states and levels of risktaking. The crosswalk safety treatment implemented over the years has used a combination of engineering, enforcement and education (the three Es).2 Although significant work to implement educational and enforcement efforts and engineering controls has been ongoing, pedestrian fatalities still account for more than 10 percent of traffic related fatalities.3
Current crosswalk engineering countermeasures focus on speed control as well as maintaining a separation between pedestrians and ve- hicles.4,5 Examples of common infrastruc- ture countermeasures include roundabouts, speed bumps, pedestrian refuge islands, multilane STOP signs and in-pavement flashing lights. Examples of common pedestrian and vehicular traffic flow countermeasures include reduced speed limits, leading pedestrian intervals, exclusive pedestrian phases, adequate traffic signal timing and pedestrian prompting devices.6
Studies have shown that these technologies provide positive measures for increased pedestrian safety. For example, research by Markowitz et al. found a statistically significant injury reduction after the implementation of a "countdown" system in a city's intersection signals.7
An assumption by roadway designers has been that pedestrians will allocate appropriate attention to their surroundings, thus allowing these features to have a meaningful impact on their behavior. A diverse set of circumstances and activities may result in pedestrians not allocating appropriate attention to their surroundings. For example, eating on the run, reading a book, or being lost in thought may contribute to pedestrians missing important environmental cues that may contribute to their safety (see Figures 1 and 2).
There is projected to be an approximate five-fold increase in the number of cellular phones worldwide between die years 2000 and 2011, and currently as many as 20 percent of Americans over the age of 12 own a portable digital music player.8,9,10 The recent boom in the sales of personal mobile electronic devices (PMEDs) offers an additional source of potential distraction for pedestrians who multitask while walking to their destination.
DIVERSITY AMONG THE POPULATION OF CROSSWALK USERS
Over the years, research findings have been used by roadway designers to accommodate the abilities and limitations of pedestrians. For example, studies have sought to characterize the function of perceptual systems, such as those underlying human vision and audition, and these data have been considered alongside environmental conditions (e.g., lighting or road noise) during the planning of crosswalks. In doing so, roadway designers have been able to characterize and account for the range in the pedestrian population likely to be using crosswalks.
However, continuing challenges face roadway planners despite the existence of many well-characterized behavioral patterns in the population. For example, while crossing a particular roadway may be well within the abilities of "typical" adult pedestrians, their ability to navigate the crosswalk may be limited due to environmental conditions, other pedestrians, or hindrances such as luggage. Therefore, while data on the capabilities and limitations of pedestrians of all ages may provide criteria as to a majority population to be served by crosswalks, additional factors may need to be considered. Including the interaction between mixed populations of pedestrians and the cognitive, perceptual and physical demands of walking while performing competing tasks may offer a more complete and realistic picture of crosswalk user tasks and the challenges faced when designing crosswalks.
The pedestrian population includes disabled individuals who may require additional information and/or assistance to safely cross a street. For example, for normally-abled individuals, most of the information at a crosswalk is obtained visually by watching traffic, seeing the markings and signage and observing the electric signs that indicate when it is safe to walk. Those who are visually impaired are more dependent on auditory cues such as the sound of the passing traffic and, potentially, sounds generated by the crosswalk signaling system. The special needs of disabled individuals have inspired roadway designers to create new and innovative technologies to meet their needs.
For example, MUTCD has defined accessible pedestrian signals (APS) as devices communicating "information about pedestrian timing in nonvisual format such as audible tones, verbal messages, and/or vibrating surfaces."11 APS in the United States currently include pedhead-mounted, pushbutton integrated, receiver-based and vibrotactile only. Of these, speakers attached to pedestrian signais (known as pedhead-mounted) are die most common.12 For crosswalks equipped with auditory signaling, the placement of the signal, as well as the type of auditory cue it produces, contributes to its effectiveness for visually impaired individuals.13
Barlow and Franck discuss how the APS supply information regarding the signal status but cannot substitute for the other information gained from environmental cues. Survey data have shown that it is common for visually impaired individuals to have trouble knowing when they should begin to cross the street and have difficulty using pushbuttons.15 Auditory cues are pertinent for these individuals to determine traffic flow, their alignment within the crosswalk and their location within the crosswalk while they are crossing the street.16
Research has also shown that it is a common occurrence within the visually impaired population for pedestrians to begin crossing the street in the correct location and with the correct alignment but to travel outside the crosswalk by the time they reach the opposite side.17,18 Experimental studies have shown that farsided audible signals are most effective at producing accurate crossings.19
The above-described technologies were designed to meet the needs of attentive pedestrians seeking crossing information. Pedestrians who may be distracted and not attending sufficiently to the crossing task to use the available information pose design challenges to the crosswalk engineer. The list of potential pedestrian distractions is infinite and may include looking at something in a direction other than the direction of travel, reading a newspaper, waving away an insect, talking to a friend, eating, looking at one's watch, attempting to find something in a backpack, or using a PMED. Looking is not always seeing, and distraction caused by any of the above activities could result in pedestrians either failing to look or looking but failing to see.
The looked-but-failed-to-see phenomenon is not new and is not limited to pedestrians. As described in Langham et al., a simple reasoning task can present enough of a distraction to cause drivers to slow their response to an in-lane hazard.20 There has been limited research on this phenomenon in pedestrians, but current research indicates that individuals who are auditorily distracted while crossing an intersection appear to exhibit unsafe behavior (failure to look left and right, wait on curb for light to turn green before stepping into the street, etc.).21,22
While important in the overall understanding of human behavior at realworld intersections, these observational studies only suggest a covariance between behavior and cognitive distraction. To further assess this potential connection, two recently published research studies have attempted to address this issue in an experimental setting.
Kuzel et al. asked volunteers to walk through an office hallway and report on objects they perceived and details of those objects while being normally attentive, while having a casual cell phone conversation and while having a challenging cell phone conversation. The volunteers passed 1 1 out-of-place salient objects placed at eye and ground level. Prior to each trial, the subjects were told they would be tested on what they saw while walking through the hall. The results showed significant effects of conversation and level of conversation difficulty on objects recalled, details recalled and time to complete the trial.23
Nasar et al. recruited pedestrians in a real-world environment to walk a course either with or without being engaged in a cell phone conversation. Participants walked past five out-of-place objects at eye level and ground level. At completion of the course, participants were shown photographs and asked to select the photograph that contained the objects they had just passed. The results indicated that subjects noticed significantly more objects while not engaged in conversation.2 The results of these studies suggest that engaging in a auditorily distractive activity can cause pedestrians to miss salient objects in their environment.
A different study by Kuzel et al. provided a review of real-world collisions involving pedestrians who were reportedly auditorily distracted at the time. The review indicated that highly salient and expected roadway objects such as buses, police vehicles and trains have been involved in collisions with reportedly distracted pedestrians at or near standardized road crossing points.25 The data suggest that pedestrians distracted by auditory activities, regardless of their form, may not always be sufficiently engaged in the act of crossing or walking along a street to perform the task safely.
In response, researchers, enforcement officials and transportation engineers are presented with several options to meet the continuing challenge of improving the safety of distracted pedestrians, including educating the public about the potential dangers of being distracted while walking; enacting regulations to change pedestrians' behavior related to distracted walking; and/or implementing new engineering controls. Research conducted on the effects of cell phone use while driving has found that educating drivers about the hazards is more easily achievable than changing their behavior.26
The effect of the enactment of laws by some states to require hands-free use of cell phones to reduce driver distraction remains to be determined. Implementation of new engineering controls between vehicles and the roadway infrastructure may help reduce injury among distracted pedestrians by shaping driver behavior.
FUTURE CROSSWALK TECHNOLOGIES
Vehicle infrastructure integration (VII) is a current initiative by the U.S. Department of Transportation to develop active safety technologies and create a communications infrastructure where data are transmitted between vehicles and the roadway.27 One particular area of VII that may be able to address the needs of the distracted pedestrian is Cooperative Intersection Collision Avoidance Systems (CICAS). These systems are both vehicleand infrastructure-based and would seek to warn drivers about likely violations of traffic control devices and/or potentially inform drivers about the existence of pedestrians within an intersection.28
Implementation of CICAS consists of vehicle-based technologies and systems; infrastructure-based technologies and systems; and communications systems to provide warnings and data between the infrastructure and equipped vehicles. Such technologies would serve to warn drivers of a potentially harmful situation so that they can devote their full attention to their environment, react appropriately to the task at hand and hopefully avoid an adverse event. These systems would in essence attempt to prompt drivers to allocate their attention to the roadway in the event of an impending collision.
These technologies are currently under investigation but have not been fully evaluated to determine their utility in real-world situations. It is interesting to note that much of the focus of the new technological developments is related to human factors issues; namely, alerting drivers to pay more attention when it is most critical to avoid a collision.
Current crosswalk features and technologies are capable of assisting diverse populations in safely crossing a roadway, and new technologies are currendy under development. One important consideration in crosswalk design and implementation is human behavior. Research conducted during the last century has supplied the information necessary to design crosswalks that meet the needs of much of the pedestrian population. Many current and potential future technologies are focused on helping make pedestrians more aware of their surroundings. Having an understanding of how distractions affect pedestrianintersection interactions is important in evaluating such technologies.
Recent research has sought to increase our understanding of the behaviors and performance capabilities of PMEDdistracted pedestrians. By making the choice not to engage in distractive activities while crossing the street, pedestrians can make intersections and crosswalks safer for themselves. Regardless of the safety technologies available at a given crosswalk, one clear way to reduce potential accidents due to inattention is to have both pedestrians and drivers choose not to engage in activities that may distract them.
The authors would like to extend their gratitude to Emily Courtois and Margaret Lehn for their assistance in reviewing this manuscript and to Michael Drzal for providing rhe photographs.
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