Exponent Article

Exponent Article

By: David Cades, Ph.D. – Managing Scientist, Human Factors

By: Emily Skow, Ph.D. – Managing Scientist, Human Factors

By: Robyn Brinkerhoff, Ph.D. – Managing Scientist, Human Factors


Understanding the Effects of Mobile Technology on Walking and Driving

The proliferation of mobile technology and its use while performing other everyday tasks has become increasingly widespread. It seems that each day we become more and more reliant on our devices to simply get through the day – with use that spans across our personal and professional lives. It is now commonplace to use a mobile device while engaging in other, often safety-critical, activities, such as driving and walking. Think about how often you have observed a driver or pedestrian staring at or talking on a cell phone or some other mobile device while driving or walking. Due in part to the increasing use of these devices, as well as evidence of significant adverse consequences of mobile device use during other tasks, research, regulations, and litigation related to driver and pedestrian distraction are also becoming more common. Decades of research have demonstrated behavioral detriments associated with distracted driving (e.g., slower reaction times, poorer visual scanning), and accident data reveals that approximately a quarter of automobile accidents are associated with cell phone usage.[1] Further, almost every state has some form of regulation limiting the use of mobile devices while driving.

More recently the effects of distracted walking have garnered increased attention. For example, in 2015 the National Safety Council added distracted walking to its annual report of unintentional deaths and injuries.[2] In addition, there have been a number of reports in the media about people walking into or tripping over objects and even falling off train or subway platforms while using mobile devices, as well as reports of serious injuries and deaths related to mobile device use – for example, a man falling off a cliff to his death while taking a photo with his phone in California.[3]

The potential for accidents and safety implications resulting from distracted behavior underscore the importance of providing insight and understanding regarding underlying human factors principles relevant to our ability to successfully engage with mobile technology while driving and walking. This article will detail those principles, provide results from recent human behavioral research, and discuss their implications for accident investigation and litigation involving distracted driving and walking.

Principles and Effects of Distracted Driving and Walking

As described above, accumulating evidence relating adverse outcomes and accidents to distracted driving and walking has begun to gain attention; a human factors analysis can help explain how and why distraction leads to these accidents. To accomplish this, human factors scientists investigate the cognitive and perceptual underpinnings upon which successful driving and ambulating rely. For example, in order to operate a motor vehicle or walk in the world, human behavior is guided by a number of cognitive processes including visual perception, attention, and motor control. Both walking and driving require the ongoing processing and integration of visual information while moving – i.e., an individual must attend to and scan the environment for hazards and determine how to navigate safely within the environment while maintaining certain parameters such as intended speed, position and path. People are only able to attend to a limited amount of information at any given time and distraction can cause failures in the ability to notice or detect even conspicuous objects. For example, sometimes an individual can focus his or her eyes on an object or a hazard, but still not "see" or detect it because mental resources are occupied elsewhere, and thus not adequately engaged in the additional perceptual processing required to become aware of the object.[4] While successful deployment of attention is a necessary component of accident and injury avoidance; it alone is not sufficient. There must also be adequate time, such that in the event that a hazard or obstacle is detected, the person will have time not only attend to the obstacle, but also to decide on and execute an appropriate response to avoid accident or injury.

The human factors principles discussed above generally apply to driving and walking as well as many other activities, and are affected by distraction. However, for walking specifically, additional factors must be considered in light of distraction, including how looking behavior, foot falls, or gait change in light of both environmental obstacles and reductions in attention and how these changes contribute to the potential for slips, trips, and falls, or their avoidance. For example, pedestrians often change their point of visual fixation, scanning the environment for such information as the presence and attributes of obstacles, surface characteristics (e.g., water/ice), path identification, and lighting conditions;[5] and based on the acquired information, such as detected obstacles or hazards, necessary modulations and corrections to gait can occur. Such modifications include avoidance maneuvers such as adjustments to step length, width, and/or ground clearance and changing direction of gait, rotation of the body, or stopping.[6]

Any time that a driver or pedestrian is engaged in another potentially distracting task, including interacting with mobile technology, there is a reduction in the cognitive resources available to focus on the primary task (i.e., driving or walking). For example, previous research has shown that a distracted driver has slower responses and higher non-response rates to critical events and hazards, decreased ability to safely negotiate gaps in traffic, and reduced scanning behavior.[7] Likewise, research has demonstrated that pedestrians engage in less safe intersection crossing behaviors while engaged with their mobile devices, including crossing more slowly, looking at traffic and other environmental obstacles (e.g., curbs) less often, and exhibiting poorer foot position consistency from stride to stride.[8] Taken as a whole, the cognitive, perceptual, and attentional detriments associated with distraction manifest in similar ways for both driving and walking behavior.

Reactions to Distracted Driving and Walking

In response to the increasing incidence of accidents involving distraction due to mobile device use, laws have been enacted aimed at discouraging such behavior, particularly for drivers. According to the Insurance Institute for Highway Safety[9], as of July 2016, 14 states and the District of Columbia have banned talking on a hand-held cellphone while driving, 46 states and the District of Columbia have banned text messaging while driving, and many localities have enacted their own bans on cellphone use or text messaging while driving. According to news reports, bills to similarly prohibit texting while walking have been proposed in New York, Arkansas, Illinois, and Nevada but were not successful.[10] Hawaii has a pending bill proposing a $250 fine for pedestrians crossing the street while using an electronic device, while another bill proposed by a New Jersey congresswoman would punish text-walkers with a $50 fine and persistent offenders with 15 days in jail.[11] One New Jersey town (Fort Lee) established a law in 2012, allowing tickets for "dangerous walking" to be issued, to include texting and walking.[12] As a playful commentary on the phenomenon of cellphone-distracted pedestrians (sometimes referred to as "pedtextrians"), several locales have introduced separate painted lanes on the ground for pedestrians using phones.[13] For example, a university in Utah painted their student center's staircase so that it was divided into three sections, one for walkers, one for runners, and one for texters. A similar idea was implemented on the sidewalks of a Chinese city, by National Geographic Television in Washington, D.C., and by a mobile phone repair company in Antwerp, Belgium. Notably, officials for those projects noted that most people did not obey the lanes, and many did not even notice them (often, ironically, due to being occupied by their phones).

Exponent's Distracted Driving and Walking Research

In line with the increased attention to distraction from mobile devices for walking and driving, our own human factors research programs at Exponent have also recently focused on expanding knowledge of not only the effects of distraction on driving and walking, but also on the utilization of technology aimed at mitigating the deleterious effects associated with distraction. We have conducted research specifically aimed at characterizing the changing nature of driving, with the advent of Advanced Driver Assistive Systems (ADAS) in vehicles (e.g., collision warning and autonomous braking, lane departure warning, adaptive cruise control, etc.), as well as how the constant and ubiquitous use of mobile technology while walking can lead to changing behavior on foot.

With respect to driving, the issue of distraction has been long-studied; however, recent advances in autonomous and semi-autonomous vehicle technology are changing the role of the driver in the vehicle. Specifically, safety systems are being introduced into vehicles aimed at combatting the negative effects of driver distraction by having the vehicle take over if and when the driver does not respond quickly enough. For example, if a driver fails to brake in response to hazard in front of his vehicle, whether because he is distracted or for any other reason, a vehicle with autonomous braking can automatically apply the brakes and either avoid or minimize the severity of a collision. Our on-road, closed-course experiments, which required participants to drive with ADAS technologies while performing different types of distracting tasks (i.e., talking or texting on a cell phone), showed that these technologies are helpful at mitigating some, but not all of the effects associated with distractions. Overall, our findings indicate that ADAS have the potential to reduce the number and severity of collisions on the roadway, but are not a replacement for attentive driving. As an example, in our study of distracted driving with collision warning and autonomous braking, participants who were not distracted were able to respond to a lead vehicle braking in front of them before the warning system in the vehicle provided an alert. In contrast, those who were utilizing a cell phone did not respond until after the warning system in the vehicle alerted them to the impending collision (Figure 1). Interestingly, most drivers (distracted and attentive) were able to apply the brakes prior to the vehicle's automatic braking system engaging.

Figure 1. Driver response in ADAS equipped vehicle to a simulated lead vehicle braking event

In another study, the use of lane departure warnings (a system that alerts drivers if their tires touch the lane lines without a turn signal activated) was not sufficient to help distracted drivers maintain their lane position – distracted drivers did not show an improvement in lane-keeping while using the lane departure warning system. Our research program has confirmed many of the negative effects associated with distracted driving and shown that recent advances in vehicle assistive and safety technology may help mitigate some of these effects, but it also demonstrates that systems such as these are not a replacement for alert and attentive drivers.[14]

Human factors scientists at Exponent have also been studying how mobile device use affects ambulation. These studies have demonstrated that walking while using mobile devices leads to changes in how we walk – both in terms of visual behavior, as well as motor behavior, and gait. In one set of experiments, pedestrians were outfitted with a wireless eye-tracking device as well as a motion capture suit to capture their motor behavior, gait and eye movements as they approached a variety of obstacles (e.g., a short staircase, a curb) while either texting or not texting (Figure 2).[15]

Figure 2. Participant texting while traversing an obstacle in our motion capture laboratory with head mounted eye-tracker.

While texting, the participants scanned a narrower area ahead of them, and spent significantly less time looking at the obstacles as they approached them (Figure 3). These findings suggest that mobile device use can reduce pedestrians' visual attention to important areas along their future travel path, which may lead to a reduced awareness of the characteristics of the environment, and sometimes, a failure to detect an obstacle in time to avoid it. Another study utilizing a different set of wireless motion capture technology to characterize pedestrians' movements and gait while either texting, talking on a cell phone, or without using a cellphone.[16] Texting was found to produce a more conservative walking pattern – for example, slower walking speeds and shorter strides than the user's typical pattern – while talking on the cell phone did not (Figure 4). These results suggest that pedestrians may adjust their walking behavior in an effort to counteract the visual impairments introduced by texting. Taken together, studies, such as these, provide valuable insight into how mobile device use affects human behavior relevant to ambulation and obstacle avoidance, and can be used to help understand why falls happen, the role of the human in those accidents, and how they may be prevented.

Figure 3. Average time spent looking at a curb surface ahead when walking without texting (blue) and when walking while texting (orange)

Figure 4. Average pedestrian gait speed (top) and stride length (bottom) when walking without texting (blue) and when walking while texting (orange).

What this means for accident investigation and litigation?

Traditionally, human factors investigations of accidents delve into areas including the role of lighting, age, conspicuity, visibility, attention, perception, decision making and many more. Understanding the effects of distraction is actually the application of a combination of many of these traditional human factors principles. The proliferation of mobile technology, combined with people's tendency to constantly be using that technology, has dramatically increased the prevalence and opportunity for distraction-related accidents, leading to an increase in public attention to this area and intensifying the need for human factors investigation. 0Our own research has shown how new technology and mobile device use is changing the nature of driving and walking, in such areas as movement control and visual scanning behavior. As human factors scientists, we can integrate this understanding of the role and consequences of mobile device use into our analyses of accident causation, and use such knowledge to help explain to juries how these human factors may have contributed to the cause of an accident. It is becoming increasingly important in investigations of accidents where mobile device use or distraction may be a factor to preserve the devices themselves and request detailed phone records that often go beyond the standard billing records. This type of information can assist in the human factors assessment of either use or non-use of a device at critical points in time. Understanding the effects of mobile device use on attention and perception is essential for understanding the human factors of a case.


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Cades, D.M., Crump, C., Lester, B. D., Reed, S., Barakat, B., Milan, L. & Young D. (in press). Differing Perceptions of Advanced Driver Assistance Systems (ADAS). To be in Proceedings of the Human Factors and Ergonomics Society Annual Meeting.

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[1] National Safety Council, 2016

[2] National Safety Council, 2016

[3] Tatro & Fleming, 2015

[4] Lanagan-Leitzel, Skow & Moore, 2015; O'Regan et al., 2000

[5] Patla, 1997

[6] Patla & Vickers, 1997; Marigold & Patla, 2007; Marigold, 2008; Patla, 1991

[7] Strayer et al., 2003; Strayer et al., 2011; McKnight & McKnight, 1993; Brown et al., 1969; Copper & Zheng, 2002; Recarte & Nunes, 2000;

[8] Neider et al., 2010; Hatfield & Murphy, 2007; Schabrun et al., 2014; Perlmutter et al., 2014

[9] IIHS, 2016

[10] E.g., Matyszczyk, 2016

[11] E.g., Matyszczyk, 2016

[12] E.g., Ngak, 2012

[13] E.g., Kaplan, 2015

[14] For reviews and more details on this research see: Crump et al., in press; Cades et al., 2016; Barakat et al., 2015; Crump et al., 2015; Crump et al., 2014.

[15] Kim et al., (in press); Lester et al., 2016

[16] Perlmutter et al., 2014; Hashish et al., 2016

Categories: Volume 7-2

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