The maximum permitted length of trucks on Canadian roads has increased significantly over the past 20 years. This has led to concern regarding the interaction of trucks with other elements in the traffic stream. This paper presents a summary of the effect of increased vehicle length on passing operations and, specifically, it looks at the effect on passing‐sight‐distance requirements of increasing the overall maximum vehicle lengths from 23 m to 25 m. Passing‐sight‐distance requirements were calculated based on generalized versions of models developed by Lieberman, in 1982, and Glennon, in 1988. The inherent random nature of vehicle and driver characteristics were incorporated into the passing model by conducting a discrete stochastic simulation of the passing maneuver. The results of the modeling exercise indicate that passing‐sight distances are considerably greater when passing a long truck than when passing a car. However, whether the truck is 23 m or 25 m long does not have a significant impact on the passing‐sight‐distance requirements.
In April 1990, the Transportation Association of Canada initiated a project to evaluate the effects of overall truck length on safety and level of service on two lane, two-way roads in Canada. The specific objectives were: 1) to determine if current intersection design and signal timing practices are adequate for vehicles longer than those presently permitted, and 2) to determine if current passing sight distances and pavement marking practices are adequate for overtaking vehicles longer than those presently permitted. Specific emphasis was placed on the implications of extending overall vehicle maximum length from 23 to 25 metres. The key findings were as follows: 1) an increase in maximum vehicle length from 23 to 25 metres would have little significant impact on the operation of intersections; 2) the impact of truck length on passing operations on two-lane highways is dependent on the geometric design standard and operating speed of the highway, and as the operating speed increases, the sight distance required to pass vehicles also increases; 3) at operating speeds over 80 km/h, the existing passing zone pavement markings may not provide adequate sight distance for passing 23 metre trucks, and an increase in maximum vehicle length to 25 metres would marginally increase this inadequacy; and 4) standards for passing sight distance and passing zone markings have traditionally been established based on one car passing another car, and it is recommended that these standards be reevaluated to take into account the maximum length of truck combinations in the Canadian fleet.
Papers presented at this session include the following: An analysis of the use of daytime running lights in the CVA fleet in Saskatchewan (Sparks,GA, Neudorf,RD, Smith,AE and Parker,G); Testing and safety/monitoring devices in the U.S. : driver and industry perspectives (Capelle,RB and Beilock,R). (TRRL)
This report contains the results of a study to develop an improved data base and understanding of truck related accidents in Saskatchewan, Canada. The investigation method utilized was determining over-the-road accident rates. The specific objectives were: to quantify the number and type of accidents involving large trucks; to develop estimates of accident rates for large trucks; to compare the accident experience of large trucks operating in Saskatchewan with the experience of other vehicle types in Saskatchewan and large trucks operating in other jurisdictions; and to identify and quantify any safety related problem areas respecting large trucks operating in Saskatchewan. Some of the study findings were as follows: most of the serious accidents involving large trucks occurred in rural areas; large trucks were involved in relatively few accidents in total, but were involved in a disproportionate number relative to their proportion in the total vehicle fleet, and further were involved in a disproportionately large number of the serious accidents; large trucks experienced about the same number of accidents per million km of highway travel as the vehicle population as a whole; the accident experience of large trucks operating on Saskatchewan provincial highways is about the same as large trucks operating on the interstate highway system in the U.S.; major contributing factors to accidents involving large trucks are human conditions (32%) and environmental factors (40%), with about 35% of large truck accidents related to vehicle type, vehicle configuration or vehicle stability; double trailer combinations experienced significantly less accidents per million vehicle km of travel than single trailer units; and, in general, vehicle type and configuration played a much less important role in the overall accident experience of large trucks than generally perceived by the public and transportation professionals.
The problem of determining optimal pavement maintenance and rehabilitation strategies is a special case of a more general problem termed the asset depreciation problem. Perhaps the most general formulation and solution of the asset depreciation problem is the semi-Markov formulation. This paper illustrates how the semi-Markov formulation and solution of the general asset depreciation problem can be applied to pavements. The semi-Markov formulation, like the Markov formulation, characterizes pavement deterioration probabilistically and represents human intervention (maintenance and rehabilitation) as slowing or modifying the basic probabilities of deterioration. The Markov formulation, first implemented for the state of Arizona, is shown to be a special case of the more general, less computationally intensive semi-Markov formulation. The application of the semi-Markov formulation is illustrated at the project level for a heavy-duty pavement in Manitoba. Key words: asset depreciation, infrastructure management, pavement management, probabilistic modelling, Markov, semi-Markov, maintenance optimization, project level.
In April 1990, the Transportation Association of Canada initiated a project to evaluate the effects of overall truck length on safety and level of service on two-lane, two-way roads in Canada. The specific objectives were: 1) to determine if current intersection design and signal timing practices are adequate for vehicles longer than those presently permitted, and 2) to determine if current passing sight distances and pavement marking practices are adequate for overtaking vehicles longer than those presently permitted. Specific emphasis was placed on the implications of extending overall vehicle maximum length from 23 to 25 metres. The key findings were as follows: 1) an increase in maximum vehicle length from 23 to 25 metres would have little significant impact on the operation of intersections; 2) the impact of truck length on passing operations on two-lane highways is dependent on the geometric design standard and operating speed of the highway, and as the operating speed increases, the sight distance required to pass vehicles also increases; 3) at operating speeds over 80 km/h, the existing passing zone pavement markings may not provide adequate sight distance for passing 23 metre trucks, and an increase in maximum vehicle length to 25 metres would marginally increase this inadequacy; and 4) standards for passing sight distance and passing zone markings have traditionally been established based on one car passing another car, and it is recommended that these standards be reevaluated to take into account the maximum length of truck combinations in the Canadian fleet.
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