Scholarly Work - Civil Engineering
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Item Passenger car equivalents for heavy vehicles at freeways & multilane highways: some critical issues(Institute of Transportation Engineers, 2006-03) Al-Kaisy, AhmedOne of the important issues affecting the accuracy of traffic analyses is heterogeneity in the vehicular traffic mix that composes a traffic stream. Typically, the majority of vehicles in a traffic stream are passenger cars or vehicles that are similar to passenger cars in physical characteristics and performance, such as sport utility vehicles, pick-up trucks and minivans. Heavy vehicles, which usually constitute the remaining smaller proportion of a traffic mix, are larger in dimension and often inferior to passenger cars in performance. Heavy vehicles consist mainly of trucks used in freight transportation, larger buses and recreational vehicles. Despite being the smaller proportion of vehicular traffic, heavy vehicles are known for their important impacts on the traffic stream. Historically, the effect of heavy vehicles on traffic flow has been accounted for through the use of passenger car equivalency factors. These factors are intended to approximate the effect of heavy vehicles and are expressed as multiples (of the effect) of an average passenger car. In the United States, the Highway Capacity Manual (HCM) provides passenger car equivalents (PCEs) for use in capacity and level of service (LOS) analyses. Using PCEs, a heterogeneous mix of vehicles in a traffic stream can be expressed in a standardized unit of traffic, such as passenger car. PCEs are considered essential in carrying out most traffic analyses.Item Static warning signs of occasional hazards: do they work?(Institute of Transportation Engineers, 2008-06) Al-Kaisy, Ahmed; Hardy, Amanda; Nemfakos, CharlesHighway agencies expend significant resources on the installation, upgrading and maintenance of traffic control devices. To ascertain that those resources are well invested, it is important to know whether traffic control devices serve their intended purpose. The answer may be easy for some traffic control devices such as traffic signals, regulatory signs and guide signs, but it may be more difficult for other devices such as warning signs in general and those intended for occasional hazards in particular. Examples of these occasional hazards are railroad crossings, icy bridges, unexpected alignment and/or geometry, falling rocks, wildlife crossings, etc. For regulatory and guide signs, drivers feel an “obligation” to use the information provided by those signs; in the case of warning signs, the use of information and drivers’ reactions seem to be based more on perception of risk. The effectiveness of static warning signs for occasional hazards is questionable because those signs typically are posted with out the hazard being perceived by drivers. Subsequently, highway agencies have begun to question the feasibility of expending significant resources on the installation and maintenance of these signs when little evidence exists regarding their effectiveness in improving highway safety. Knowing the effectiveness of these signs in improving safety is important for highway agencies to assess the feasibility of using conventional signs and whether alternative warning devices are required for a safer highway environment.