Ability of various truck configurations to negotiate rural roads with restrictive geometry was examined in addition to effects of such trucks on traffic operations and safety. Truck sizes included truck-tractor semitrailers with trailer lengths of 40, 45, and 48 ft (i.e., Semi-40, semi-45, and semi-48) and twin-trailer combinations with 28-ft trailers (i.e., Twins or double 28). Test sites consisted of approximately 60 mi of rural, two-lane roads in new jersey and california with a variety of lane widths, shoulder widths, and horizontal and vertical alignment. Field testing involved following control trucks of each truck type along the selected routes. Photographic and radar equipment were used in a data collection caravan to measure the effects of the trucks on oncoming vehicles in terms of speed changes and lateral placement changes. Statistical testing was used to compare operational differences between various truck types for specific geometric conditions. Results showed that semi-48 and twins caused some changes in operation of oncoming vehicles, particularly on narrow roadways. However, careful driving by drivers of larger trucks may have partially compensated for operational differences in oncoming vehicles between truck types. Overall, truck driving behaviour and site differences had more of an effect on vehicle operations than the effects of the different truck types. Potential safety problems as evidenced by extreme manoeuvres were observed for a few oncoming motorists in reaction to the twins and longer tractor semitrailers. This paper appears in Transportation Research Record No. 1281, Human Factors and Safety Research Related to Highway Design and Operation 1990.
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