Civil Engineering License Review, Fifteenth Edition
Including essay and multiple-choice exam problems, this review book offers a detailed discussion of the Civil Engineering/Professional Engineer Exam and how to prepare for it.
TABLE OF CONTENTS Civil Engineering License Review, Fifteenth Edition
HIGHWAY SYSTEM CHARACTERISTICS AND DESIGN CONTROLS
The characteristics of traffic flows on the highway system are the results of complex interactions between the following three basic elements: drivers, vehicles, and the roadway itself. Effective transportation engineering requires an understanding of these three elements and the traffic flows resulting from their interactions.
Driver Performance
The perception of, and reaction to, cues and stimuli encountered by the driver of a vehicle involve four distinct actions: perception, identification, emotion or decision (determination of appropriate response), and volition (reaction). The total time taken for this sequence is referred to as PIEV (perception, identification, emotion, and volition) time or perception-reaction time. Perception-reaction time is an important factor in the determination of braking distance, which in turn dictates minimum sight distance and the length of yellow phase at signalized interactions. The distance traveled during this time is calculated from the following equation:
where
| d p | = perception-reaction distance (m or ft) |
| v | = speed of vehicle (km/hr) |
| t | = perception-reaction time (sec) |
| 0.278 | = conversion factor (km/hr to m/sec) |
| 1.47 | = conversion factor (mph to ft/sec) |
In most situations, a PIEV time of 2.0 to 2.5 seconds is considered realistic. The American Association of State Highway and Transportation Officials (AASHTO) recommends a value of 2.5 seconds for design purposes (AASHTO, 2001). The AASHTO Policy on Geometric Design of Highways and Streets (2001) is the standard reference in the field of geometric design. It should be one of the reference documents taken to the exam.
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