National Academies Press: OpenBook

Human Factors Guidelines for Road Systems: Second Edition (2012)

Chapter: Chapter 3 - Finding Information Like a Road User

« Previous: Part II - Bringing Road User Capabilities into Highway Design and Traffic Engineering Practice
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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Suggested Citation:"Chapter 3 - Finding Information Like a Road User." National Academies of Sciences, Engineering, and Medicine. 2012. Human Factors Guidelines for Road Systems: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22706.
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3.1 Introduction Some people have said the primary decision-maker in the highway transportation system is the road user. But this statement is just not true. It is not true because many primary decisions are made before the road user ever sees and uses the road. During design and/or reconstruction, primary decisions include the magnitude of the vertical and horizontal alignment, the type of traffic control, and the vehicles permitted on the facility, among others; these decisions are made by highway designers and traffic engineers. The purpose of this chapter is to remind users of the HFG that road users must read and com- prehend from the roadway what the highway designer and traffic engineer intend for them to do. Unfortunately, the road users are not highway designers or traffic engineers and what they comprehend, while totally logical to them, may not be what the highway designers and traffic engineers intended. In short, this chapter illustrates that highway designers and traffic engineers must work together and serve as virtual road users if their goal is to maximize or improve high- way safety. This chapter will show through examples why the highway designers and traffic engi- neers must jointly consider how their individual work may be interpreted by the road user and whether that interpretation promotes user safety. 3.2 Road User as a Component of the Highway System Highway systems have three major components: the road, traffic control, and users with or without a vehicle (Figure 3-1). For the highway system to operate efficiently and safely, each of these components must work together as a combined unit. This task is not easy, largely because of the wide range of roadway environments, vehicles, and users. Highway systems are composed of local roads, collectors, arterials, and freeways—each having specific design fea- tures suitable for their environment. Vehicles using the roads vary widely with respect to weight, size, and performance. Vehicles using the roads may be small, light-weight vehicles with limited power; moderate-size and -powered vehicles; or large, heavy trucks with the horsepower to permit high speeds. Also, the population of road users includes car and truck operators, pedestrians, motorcycle operators, and bicycle riders, all, sometimes, with some degree of physiological disability. If the goal is to provide highway travel for road users that is both safe and operationally effi- cient, the needs and constraints of highway design, traffic control, and users must be successfully integrated. Together they must perform as one—not a group of three. Highway designers must know the impact of their design decisions and how they will affect the control needs of traffic engineers as well as the resulting impact they will have on users in performing efficiently and 3-1 C H A P T E R 3 Finding Information Like a Road User

safely. Traffic engineers cannot be expected to solve design problems with traffic engineering fixes. Safe roads are those that are self-explaining where users know how to behave solely because of the design and control of the road (Theeuwes & Godthelp, 1992). Road users cannot be expected to solve either highway design or traffic engineering problems without making mistakes and/or compromising operational efficiency and safety. Highway system failure in the United States can be measured by the 42,000 fatalities, 3 million injuries, 6 million police-reported crashes, and many more unreported crashes that occur annually (NHTSA, 2004). System failures can be attributed to errors by drivers, design, traffic control, and combinations of these factors (Hauer, 1999). Design and operation solutions must be jointly developed by highway designers and traffic engineers with both totally aware and cognizant of the needs and limitations of all road users. In effect, they must incorporate into their joint solutions human factor principles that are in keep- ing with the needs of all users. 3.3 Example Problems of Highway Designers and Traffic Engineers The following examples illustrate typical design and operational problems where considera- tion of good human factor principles is appropriate. • An intersection with the crossing road at an acute angle (30°) has experienced an unusually high number of crashes. See Figures 3-2 and 3-3. The county supervisors have asked the local highway agency for a review and recommendation on what should be done to correct the problem. After reviewing the site, the current and projected traffic flow, and the expected land development in the area, the agency recommended the intersection be changed. Options con- sidered included using stop control on each approach, signalization, and redesign. Neither all-way stop control nor signalization met the MUTCD warrants; therefore, they were discarded as options (FHWA, 2009). Research literature indicates that drivers have difficulty estimating gap size and speed of approaching vehicles at intersections where intersecting roads are not within about 25° of normal (Pline, 1992). The recommended solution was to redesign the crossing road approach to eliminate the acute angle so the approach would be nearly perpen- dicular to the major road. HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 3-2 Traffic Control Road User-Pedestrian User-Car User-Truck Figure 3-1. Example components of the highway system.

• Each end of a 1-mi section of two-lane road in a suburban area had been improved to a four-lane divided highway. The remaining two-lane road had very bad vertical curvature and a cross section with very narrow shoulders; thus the two-lane road environment was very different from either the upstream or downstream road sections. The speed limit was 40 mi/h within the two-lane section and the newer four-lane sections. The two-lane section seemed to have a higher than normal number of crashes. The highway agency requested that the safety, design, and traffic engineers review the roadway and provide recommen- dations on what should be done. The crash occurrence during the day was found to be not unusually high. At night, however, this was not the case. Drivers approaching the sharp, vertical crests were running off of the road and hitting roadside objects. The engineers rec- ommended that advance curve warning signs, vertical delineators, and roadway lighting be installed in the two-lane section to help prevent drivers approaching crests at night from being overcome by sudden glare produced by opposing vehicles previously hidden in the sags as shown in Figure 3-4. 3-3 HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 Original Figure 3-2. Northbound approach to example intersection. Figure 3-3. Westbound approach to example intersection.

Some human factor characteristics regarding roadway users are available to help implement preferred design and control solutions. The following are some of those found in the research literature: • Drivers experience difficulty at intersections in estimating gap size and speed of approaching vehicles (Staplin, Lococo, & Byington, 1998). • Drivers experience problems in detecting a sharper curve after negotiating several longer radius curves (Glennon, 1996). • Additional distance and time are required to slow or stop under adverse weather conditions (Baerwald, 1965). • Excessive messages on changeable message signs (CMSs) can inhibit correct decisions and traffic flow, and safety (Staplin et al., 1998). • Bright light sources, whether from vehicles or roadside property, can cause glare, user-blinding, and possible loss of vehicle control (Ogden, 1996). While the previous items and two examples are not an exhaustive list, they illustrate a few of the many user problems encountered. Highway designers and traffic engineers must be aware of such human factor characteristics and use them in a way that will improve or optimize the safety of the road system they are designing and controlling. 3.4 How Road Users Seek Information Theeuwes and Godthelp (1992) have described self-explaining roads as road environments where users know how to behave based on the road design. Unfortunately, many roads today are not self-explaining. Self-explaining roads induce user behavior based on the design and not on “external agents” like signs and traffic signals. When the road is not self-explaining, highway operations can be inefficient, delayed, and unsafe, plus user speeds are more varied. Road users continuously seek information under many different conditions—from when the road envi- ronment has few vehicles or other users present to when many vehicles and other users are present; however, road users’ access to information may be more difficult under conditions of darkness, inclement weather, glare from sunlight, etc. According to research findings, users categorize roads during their driving task and formulate their temporal reactions based on pre- viously learned behavior (Theeuwes & Diks, 1995). Design standards by functional classification enhance user-learned behavior and their system expectations. Road users seek information for navigation, guidance, and control (Alexander & Lunenfeld, 1990). Navigation information relates to getting from point A to B; guidance information relates HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 3-4 Figure 3-4. Day and night views of approaching crest.

to lane selection; and control relates to selection of vehicle speed, level of braking, and steering. The information road users seek varies according to the situation—sometimes complex and sometimes simple. How road users seek information is fairly simple. They scan the road environment seeking the most meaningful information (MMI) needed for that particular road location and point in time. How they scan the environment depends on the presence or absence of potentially hazardous situations as they perceive them. Road users are generally alert for both longitudinal and lateral hazards (i.e., other vehicles, pedestrians, animals, or objects near their planned path); they develop an expectancy of the roadway based on what they previously experienced upstream. They seek the information they need by searching the road environment in front of, behind, and to the sides of the vehicle they are driving. This searching and scanning process is continuous for the duration of the trip. Scanning of the road environment is a time-based activity. The speed at which scanning is per- formed is not constant but it is a function of the road environment (i.e., geometric design, vehi- cle speed, cross section elements, traffic volume, weather, vehicle mix, presence of pedestrians, driver experience, traffic control, etc). If the environment has no threatening activity perceived by the road user, the scanning rate may be slower, and he or she may have time for scenic plea- sures. At other times the visual scanning rate may be greater because of enhanced road environ- ment activity. Early notable research on driving scanning was conducted by Mourant, Rockwell, and Rackoff (1969). Road users can receive and process only a finite amount of information in a short time period, not an infinite set of information. To describe perception-reaction time (PRT), Johannson and Rumar (1971) use a scale ranging from 0 to 6 bits of unexpected and expected information that a road user can process per second. They found the average driver processes about 1 and 1.5 bits of information per second for unexpected and expected situations, respec- tively. The more difficult or competing tasks a road user is confronted with, the longer he/she will take to select the response to initiate; also, not all road users perform the same (Johannson & Rumar, 1971). According to AASHTO, for unexpected situations some drivers take as long as 2.7 seconds (AASHTO, 2011). Therefore, highway designers and traffic engineers must plan and develop the road environment temporally and in accordance with the scanning ability of the road users. Highway designers and traffic engineers often use distance-speed criteria (i.e., stopping dis- tance, passing distance, intersection sight distance) to specify road design elements and place- ment of traffic control devices, but distance criteria are always based on time and how road users use it. 3.5 Examples of User-Scanned Road Environments The purpose of this section is to illustrate the features that road users would classify as the MMI for making their next driving decision using a photograph of an example location. This kind of research is useful to highway designers and traffic engineers because it identifies what informa- tion road users are using and whether the individual bits of information are useful, competing, or potentially misleading to road users’ decision making and safety. The following examples were prepared by showing subjects hard copies of the roadway scenes, some with approaching vehicles and some with no approaching vehicles (Tignor, 2006). The subjects were asked to identify the most important information they would consider should they confront that situation when driving. A color code was used to prioritize the information from 3-5 HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0

most to least important. The priority of the color code was from left to right with dark green as priority one. The road is in a suburban environment and it has a speed limit of 35 mi/h. 3.5.1 Example 1, View 1 The first example illustrates what subjects identify as MMI when there is a lot of activity in the road environment. As shown in Figure 3-5, when no vehicles are moving toward the road users (middle photograph), many items are identified as possible sources of meaningful infor- mation even though the road environment has many parked vehicles, three intersections, and a distant curve. The presence of approaching vehicles (bottom photograph) changes what road users consider as important information. Approaching vehicles clearly induce the road users to concentrate their attention to them as sources of MMI. The items having the highest frequency of visual sources of meaningful information are approaching vehicles, the nearest intersections, and a distant curve. 3.5.2 Example 2, View 4 The second example illustrates how road users are adversely affected when roadway design and traffic control features are not appropriately coordinated. Figure 3-6 shows drivers approaching a very short vertical curve (top photograph) that has the potential of hiding downstream vehicles just beyond the crest of the curve. Just upstream of the crest is a speed limit sign. The colored circles in the figure (middle and bottom photographs) show that many of the sub- jects look to the speed limit sign as the first or second most meaningful source of information as opposed to the crest beyond, which could hide a vehicle or other hazard in the roadway. They look at the speed limit sign whether a vehicle is or is not ahead of them. The short vertical curve is a roadway hazard, but the speed limit sign creates an additional hazard. If the road design and traffic engineering had been coordinated, more time would have been available for the road user to seek the MMI for assessing a potential conflict at the crest. From a safety perspective the speed limit sign should be relocated. 3.5.3 Observations from Examples The previous two examples show some interesting results: 1. The selection process is different depending upon the presence or absence of other vehicles. When the roadway has no other vehicles in the forward view, the subjects’ search is longi- tudinally and laterally broad and downstream from their current road location. They are primarily seeking information for guiding and controlling the vehicle. 2. When other vehicles are within their forward view, whether approaching or traveling in the same direction, the subjects’ search is more selective. They tend to focus first on other vehicles in the road environment and second on information for guidance and control. 3. The examples illustrate how important it is for the road design and traffic control compo- nents to be coordinated to prevent competition for road user attention, which compromises user safety. 3.6 How Highway Designers and Traffic Engineers Work Together for Road Users 3.6.1 Serve as Virtual Road Users Highway designers and traffic engineers must serve as virtual road users. They must view the route in small, incremental steps as if they were road users traveling downstream and gathering HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 3-6

3-7 HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 1- Near Gordon Street 1 - Near Gordon Street 1t - Near Gordon Street Figure 3-5. Example 1, View 1.

HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 3-8 4 - Front of Shrevewood School 4t - Front of Shrevewood School 4 - Front of Shrevewood School Figure 3-6. Example 2, View 4.

information in small time and space increments; they must learn from road users’ experiences. Identifying what road users consider important is not easy. Ninety percent of drivers’ tasks are obtaining visual information from the roadway to maneuver their vehicle safely (Hartman, 1970). This visual information cannot be confusing and it must be complete and accurate if safe decisions are to be made. Road safety audits and a pro- cedure used by McGee called SLIDE (Simplified Location of Information Deficiencies) depend on professional staff to identify safety problems associated with on-road design and traffic con- trol applications and omissions (Morgan, 1999; McGee, Hughes, & Hostetter, 1986). The MMI procedure obtains information directly from road users about what in the road environment they consider important to their driving decisions. User input is important because 27% of road crashes are attributed to a joint association of road user and roadway environmental problems (Schlegel, 1993). Eye scanning technology, in both real and simulated conditions, has also been used for obtain- ing information on what drivers view in the visual field. Although vast and time consuming to decipher, eye scanning data are interesting. The literature reports on search patterns of novice and experienced drivers (Mourant & Rockwell, 1972), the degrees of longitudinal and lateral eye fixation zones (Shinar, McDowell, & Rockwell, 1977), design of controls on vehicle instrument panels (Dingus, Antin, Hulse, & Wierwille, 1989), and signing (Smiley et al., 2005). For exam- ple, Mourant and Rockwell (1972) estimated 70% of driver eye pursuits were for lateral position. Shinar et al. (1977) found lateral eye movements increase during curve negotiation on two-lane roads and they begin 2 to 3 s before entering a curve. On right turns, drivers spend 55% of the time looking at the road and only 5% looking to the left. Similarly on left turns, drivers spend 38% of the time looking at the road and 24% of the time looking to the right. Recarte and Nunes (2000) found mean horizontal visual fixation to be ± 0.5° from center with a ± 2° standard devi- ation and mean vertical visual fixation to be 1° below the horizon with a ± 1° standard deviation. Harbluk, Noy and Eizenman (2002) reported 80% of all driver fixations are within the central 15° of the visual field. Gordon (1966) reported that 98% of driver fixations fell on or near the road edge or centerline. He also reported drivers look about 6.5 ft from the right edge of the road when following a left curve, and about 9 ft from the right edge of the road when turning right. While these findings are interesting, the research analysts must infer or guess what items are really important to road users’ driving decisions. Consequently, the results from eye scanning research have not been previously incorporated into design standards and guidelines. Yet, highway designers and traffic engineers must identify jointly the important design and traffic control elements that are critical to road user decision making. They must identify poten- tially conflicting and misleading information whether it be geometric, traffic control, or the com- bination of both. The roadway environment created must provide continuous, clear information that the road user can interpret quickly, accurately, and safely. 3.6.2 Incorporate Substantive Safety and Self-Explaining Designs A substantive safe road system must be created (Hauer, 1999). When a road system is prop- erly created, potential errors will be prevented by elimination of the following: • The unintended use of infrastructure • Non-uniformity and inconsistency of design and traffic control applications • Encounters with large differences in speed • Uncertain driver behavior 3-9 HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0

Self-explaining designs create road categories that are recognizable by users and are appro- priate for the following: • Flow requirements (i.e., small to large volumes) • Speed functions (i.e., slow to high speed) • Access functions (i.e., local roads, collectors, arterials) Lastly, self-explaining roads have the following characteristics: • Road environments where road users know how to behave simply by the design • Road types in keeping with road user expectations based on visual information obtained and object conspicuity • A driving environment that is intuitive and transparent (Theeuwes & Godthelp, 1992) 3.6.3 Jointly Develop Road Systems To achieve an acceptable level of system safety, highway designers and traffic engineers need to serve as virtual road users. They must place themselves in the shoes of the road user and con- sider what the road user will identify as most important both during day and night conditions. To identify the MMI, the highway designer and traffic engineer will together need to apply prin- ciples similar to those found in road safety audits (Morgan, 1999): • Highway designers and traffic engineers must jointly develop and agree on the goals for the road system that will meet the objectives of the road agency but have the safety of users in the forefront. • Highway designers and traffic engineers must jointly develop, review, and approve the design and operational plans for each project. The designs will be self-explaining to the road users and provide substantive safety for them. • Whether projects are new construction, upgrades, or maintenance, highway designers and traffic engineers must jointly oversee the field work and make inspections as virtual road users before the start of new operations. If misleading individual or combined design and control features are found, they should be eliminated before the road is opened to traffic. HFG FINDING INFORMATION LIKE A ROAD USER Version 2.0 3-10

Next: Chapter 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs »
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TRB’s National Cooperative Highway Research Program (NCHRP) Report 600: Human Factors Guidelines for Road Systems: Second Edition provides data and insights of the extent to which road users’ needs, capabilities, and limitations are influenced by the effects of age, visual demands, cognition, and influence of expectancies.

NCHRP Report 600 provides guidance for roadway location elements and traffic engineering elements. The report also provides tutorials on special design topics, an index, and a glossary of technical terms.

The second edition of NCHRP 600 completes and updates the first edition, which was published previously in three collections.

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