National Academies Press: OpenBook

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

Chapter: Chapter 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs

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Suggested Citation:"Chapter 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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.
×
Page 23
Page 24
Suggested Citation:"Chapter 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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.
×
Page 24
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Suggested Citation:"Chapter 4 - Integrating Road User, Highway Design, and Traffic Engineering Needs." 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.
×
Page 25

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

4.1 Introduction The purpose of this chapter is to help highway designers and traffic engineers function as virtual road users. Not all road user situations are the same; some are more demanding than others. The different situations make the highway designer’s and the traffic engineer’s work more challenging, more intricate, and more demanding. They must consider the human fac- tor characteristics of the user in conjunction with four major components: (1) the geometric design elements, (2) roadway and vehicle operations, (3) type of highway, and (4) the road- way environment. At any given location, the roadway user only has a finite amount of time to make decisions. Users, even with total visual attention, may not have sufficient time, under demanding real-time conditions, to extract as much information as desired. Sometimes road users must make choices about what information is processed. The scope of this chapter is to illustrate the breadth of the human factor considerations as magnified by the four major com- ponents and how highway designers and traffic engineers must integrate them all in safety- oriented solutions given the constraints of the road user. This chapter also shows, through examples, how on-road problems can be reviewed and improved by using the recommenda- tions in Parts III and IV. 4.2 Iterative Review Steps to Achieve Good Human Factor Applications 4.2.1 Process Whether driving, walking, running, or bicycle riding, road users continuously scan the down- stream environment that they are entering (Robinson, Erickson, Thurston, & Clark, 1972). The scanning can be represented as shown in Figure 4-1. In the figure, a vehicle is proceeding from left to right. At location or time I, the user observes the road environment and corresponding traffic conditions. He or she identifies the MMI at that point in time and space and assesses what guidance and control is needed (Tignor, 2006). The user implements that control and continues with it until scanning location or time I+1 when an information refresher is determined necessary. Any number of conditions could initiate the need for an information refresher. The following are typical examples that could induce a need for new information at I+1: • The cross section may have an increase or decrease in the number of lanes. • Downstream traffic may be slowing or stopping in the lane the user is traveling. 4-1 C H A P T E R 4 Integrating Road User, Highway Design, and Traffic Engineering Needs

• A pedestrian may be walking along the shoulder and without looking turn in front of the approaching user. • Traffic may be entering the road from a side street or business establishment. • A user is approaching a traffic sign with letters that are too small to read. • A traffic signal is changing from green to amber. • The road appears to be curving sharply to the right while the lane width is decreasing. Each of these examples would necessitate that the road user reassess his or her information and control at I and determine if control modification is required. The challenge for virtual users (i.e., highway designers and traffic engineers) is to determine what kind of infrastructure modification is required, if any, from locations I, I+1, . . . I+n. The scanning step sizes may vary and are influenced by the road user, type of operation, high- way character, and environment. Some of these variables are listed in Table 4-1. All road users are continuously sampling the road environment for information. The sampling rate can be represented as follows: Sampling Rate user, operations, highway, e= f nvironment( ) HFG INTEGRATING ROAD USER, HIGHWAY DESIGN, AND TRAFFIC ENGINEERING NEEDS Version 2.0 4-2 I I+1 I+2 I+3 I+4 I+5 … I = User scanning steps (vary in size) Figure 4-1. Road user scanning steps for finding most meaningful information (MMI). User Age Cognitive ability Vision Road familiarity Experience Operations Speed One-way flow Vehicle type Two-way flow Traffic volume Control type Highway Functional class Condition Lane width Roadside Shoulder width Grades Sight distance Curvature Pavement type and condition Environment Weather Rural Land use Time of day Pedestrians Light condition Urban Scenic/interest attractions Factor Variable Table 4-1. Scanning step variables.

Through road scanning the user is updating his or her information database for making decisions. This process can be expressed as follows: Where t = time Δt = sampling interval The real challenge then is to identify the changes that have occurred during the sampling interval (Δt). Changes include those elements detected by the road user within the visual scans or I steps. They may be previously seen items or new items not seen previously. The impor- tance of the items may be elevated or reduced depending on their relationship to the user’s need at the time (t). They may have a direct impact on the user’s task of maintaining control of the vehicle or they may only serve as information useful for defining the approaching highway, oper- ating, and environmental conditions. 4.2.2 Size of Iterative Steps The highway designer and the traffic engineer must examine the road environment in incre- mental steps similar to those steps described in the previous section to ensure the road user will not be overloaded with temporal tasks and decisions. In short, good human factor principles must be integrated into the design of the road system. The sizes of the iterative steps are not going to be the same for all road environments. They will vary depending on the road user, the type of highway, the operations, and the environment. The iterative steps, however, must overlap from one section to the next to ensure continuity of the travel path and that no potentially meaningful information for road users will be overlooked. The highway designers and traffic engineers must jointly examine the road environment— i.e., lane alignment (roadway and intersections), signing (advisory, regulatory and guidance), and operations (normal and work zones)—relative to the likelihood users will be able to perform the required tasks safely and efficiently within the time and space available. Table 4-2 is a breakdown of some of the different steps taken by road users and their respec- tive time restraints. 4.2.3 Identification of Potentially Conflicting or Missing Information Identification of potentially conflicting, confusing, or missing information is probably one of the most important tasks of designers and traffic engineers. As virtual road users, designers and traffic engineers must examine the roadway environment for information conflicts that may mis- lead or confuse road users. They must anticipate what information the road user requires and where it is needed so appropriate design elements or traffic control can be integrated into the design and operational plans. Missing information is not helpful to the road user. In short, designers and traffic engineers must also seek road environments that are self-explaining, quickly understood, and easy for users to act upon (Theeuwes & Godthelp, 1992). The example and analysis detailed in the next section illustrates problems that can be created by not properly relating the roadway geometrics to the traffic control. Together, designers and traffic engineers need to identify these problems when serving as virtual road users. Information t Information t 1 changes dur( ) = −( ) + ing tΔ 4-3 HFG INTEGRATING ROAD USER, HIGHWAY DESIGN, AND TRAFFIC ENGINEERING NEEDS Version 2.0

4.3 Use of Parts III and IV for Specifying Designs Parts III and IV are where explicit guidance statements are found. Before using the HFG for developing a solution to a problem, the HFG user must first study and understand the issues involved. For example, the illustrative example in section 4.3.1 involves both geometric design and signing issues. The approaching road users see a fork in the road and seven sets of signs com- municating information to drivers. Because the signs are spaced too close together and the road is making an abrupt turn to the left, approaching drivers have insufficient time to scan the envi- ronment and make decisions on navigation, guidance, and control. Part III, Chapter 6, Curves, and Part IV, Chapter 18, Signing, are the sections of the HFG that will be used for developing the solution to this problem. 4.3.1 Detailed Description of Illustrative Example A two-lane arterial roadway (US 293) crosses over a parkway (Route 6) that prohibits trucks. The arterial approaches the parkway from a tangent, but it then crosses over the parkway by curving sharply to the left. The connection to the parkway is a ramp that appears as a contin- uation of the arterial tangent. Because trucks are prevented from using the parkway, a sign directs them to an alternative roadway to reach the portion of Route 6 with unrestricted access. See Figure 4-2. HFG INTEGRATING ROAD USER, HIGHWAY DESIGN, AND TRAFFIC ENGINEERING NEEDS Version 2.0 4-4 Eye fixation time 0.20 to 0.25 s (Homburger & Kell, 1988) 0.25 to 0.33 s (Mourant et al., 1969) Turn head to the left 1.31 to 1.52 s (Mourant & Donohue, 1974) Turn head to the right 1.09 to 1.14 s (Mourant & Donohue, 1974) Car following Attention to lead vehicle reduces attention elsewhere by 15% (Mourant et al., 1969) Sign detection Look time: 0.5 s (Zwahlen, 1995; Zwahlen & Schnell, 1998) Saccade time: 0.03 s (Zwahlen, 1995; Zwahlen & Schnell, 1998) Time for fixation on sign: 0.3 to 0.8 s (Zwahlen, 1995; Zwahlen & Schnell, 1998) Sign reading Variable message signs (Staplin et al., 1998) Minimum exposure time:1 s/short word (four to eight characters) or 2 s/unit of information, whichever is larger Reading time: 1 to 1.5 s/unit of information in light traffic Minimum phase or page time: 3 s/page for a three-line message Video signs (Smiley et al., 2005) 20% of glances to video signs exceeded 0.75 s 38% of glances occurred when headways were less than 1 s 25% of the glances were at angles greater than 20° 76% of drivers looked ahead, 7% at signs and signals, 6% at pedestrians Glances at video signs occurred with longer headways than with static signs Use of mirrors 0.87 s, rear view (Mourant & Rockwell, 1972) 0.98 s, left side (Mourant & Rockwell, 1972) 0.78 s, rear view (Mourant & Donohue, 1974) 0.88 s, left side (Mourant & Donohue, 1974) Step Timing Table 4-2. Iterative steps used in sampling the road environment for information.

Various problems are found at this location: • The alignment of the arterial and parkway ramp is not self-explaining. The first route marker shows Route 6 going to the right. The first word sign, on glance, suggests Route 6 is going to the left. The first line on the first word sign indicates the sign is for trucks and trailers, but that is not immediately clear to unfamiliar, approaching drivers. Car drivers also visually key on the sign. Confusion is created as to which road is Route 6, Route 293, and Route 9W. 4-5 HFG INTEGRATING ROAD USER, HIGHWAY DESIGN, AND TRAFFIC ENGINEERING NEEDS Version 2.0 Figure 4-2. Improper signing and geometrics.

• Because of the location of the signs and their close spacing, drivers have insufficient time to identify the important information. Also, the word signs have too many lines of information for users to read and interpret. • The heights of the letters on the signs are too small. • The message as to where trucks are permitted is not sufficiently clear. • As seen by the skid marks near the gore in Figure 4-2 (bottom photograph), road users have difficulty in deciding whether to follow the road to the left or continue straight onto the ramp to the parkway. • Access to intersecting routes or ramps should not appear to be a continuation of the approach- ing, main road. Parts III and IV will be used together to develop a joint candidate design and control solu- tion having a high level of road user acceptance, understanding, and safety. Candidate solutions must be in compliance with AASHTO design and MUTCD control standards (AASHTO, 2011; FHWA, 2009). HFG INTEGRATING ROAD USER, HIGHWAY DESIGN, AND TRAFFIC ENGINEERING NEEDS Version 2.0 4-6

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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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