Stopping distance requirements for large trucks are compared with current AASHTO stopping sight distance criteria. Key elements affecting stopping sight distance for trucks include perception-reaction time, truck braking distance, and truck driver eye height. The paper stresses the variability of truck driver braking performance and the safety benefits associated with antilock brake systems for trucks. Findings indicate that trucks with conventional brake systems may require stopping sight distances greater than those recommended by current AASHTO policy. The increased values potentially affect all related stopping sight distance design considerations (horizontal and vertical curvature, intersection sight distance, and highway-railroad grade crossings). The magnitude of increase, however, is highly dependent on individual driver brake performance capabilities. For drivers whose emergency braking performance is equivalent to the worst performance observed in braking tests for conventional brake systems, substantially greater stopping sight distance and longer vertical curves would be needed than are used under current AASHTO criteria. Drivers with braking performance equivalent to the best performance observed in braking tests for conventional brake systems require only slightly longer stopping sight distance than current AASHTO criteria and require vertical curve lengths that are shorter than current AASHTO criteria. If antilock brake systems are eventually mandated for trucks, current AASHTO stopping sight distance policy would adequately accommodate the needs of large trucks.
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