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1、交通工程专业英语,Chapter 2 Characteristics and Components of Traffic Systems,Chapter 2 Characteristics and Components of Traffic Systems,To begin to understand the functional and operational aspects of traffic on streets and highways it is important to understand how the various elements of a traffic system
2、 interact. Further, the characteristics of traffic streams are heavily influenced by the characteristics and limitations of each of these elements. There are four critical components that interact in a traffic system: Road users Vehicles Streets and highways The general environment,The success of tr
3、affic engineering depends upon the coordination among the four primary components above. Their characteristics are major factors which affect the design of traffic engineering and the performance of the traffic system. To provide efficient and safe traffic system, knowledge of the characteristics of
4、 these components is essential like the driver characteristics, passenger characteristics, pedestrian characteristics, vehicle characteristics, and roadway characteristics. It is also important to analyze the interrelationships among these components in order to determine the effects.,2.1 Road Users
5、 2.1.1 Driver Characteristics Human beings are complex and have a wide range of characteristics that can and do influence the driving task. In a system where the driver is in complete control of vehicle operations, good traffic engineering requires a keen understanding of driver characteristics. Muc
6、h of the task of traffic engineers is to find ways to provide drivers with information in a clear, effective manner that induces safe and proper responses. The two driver characteristics of utmost importance are visual acuity factors and the reaction process. The two overlap, in that reaction requir
7、es the use of vision for most driving cues. Understanding how information is received and processed is a key element in the design of roadways and controls.,1. Visual Characteristics Actions taken by drivers while driving on a roadway largely depend on their evaluation of and reaction to information
8、 they receive from the stimuli that they see, feel or hear. Researcher report that about 90 percent of the information a driver obtains is visual. For details about visual information please refer to Table 2.1.,Table 2.1 Visual Factors in the Driving Task,Visual acuity is defined as the ability to s
9、ee fine details of an object. There are two types of visual acuity useful in traffic engineering: static visual acuity is the ability to read letter at certain distance; dynamic visual acuity is the ability to see objects in relative motion with the eyes. Generally, static visual acuity of a person
10、is better than his/her dynamic visual acuity, which means that the ability of drivers to clearly see things diminishes with the increase of speed. Mourant and Rockwell indicated in their study that experienced drivers scanned a wider range of horizontal fixation locations than novice drivers. The av
11、erage horizontal fixation range for the experienced group varied from 30 to 48 degrees. Visual acuity declines and the field of vision narrows with advancing age, especially when lighting conditions are poor.,Peripheral vision is defined as the ability to see objects the cone of clearest vision. The
12、 field may extend up to 90 to the right and left of the centerline of the pupil, and up to 60 above and 70 below the line of sight. This wide variation of the value results from the speed of the vehicle. The peripheral vision field narrows, as speed increases, to as little as 100 at 32 km/h and to 4
13、0 at 96 km/h. Color vision is the ability to differentiate one color from another, but deficiency in this ability, usually referred to as color blindness, is not of great significance in highway driving because other ways of recognizing traffic information devices can compensate for it.,Glare vision
14、 and recovery are also important drivers characteristics. Typically, direct and specular glare visions are the two types of glare vision. Direct glare occurs when relatively bright light appears in the individuals field of vision. Specular glare occurs when the image reflected by the relatively brig
15、ht light appears in the field of vision of a driver. Both types of glare result in the deterioration of visibility and cause discomfort to the eyes. Glare recovery is defined as the time required by driver to recover from the effects of glare after passing the light source. Studies show that this ti
16、me is about 3 seconds when moving from dark to light and 6 seconds or more when moving from light to dark. Street lighting is designed for minimizing glare effects.,Depth perception affects the ability of a person to estimate speed and distance. It is particularly important on the two-lane highway during passing maneuvers, when head-on crash may result from a lack of proper judgment of speed and distance.,2. Perception-Reaction Time (PRT) The second critical driver characteristics is perceptio
