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Published: 1996

Total Pages: 86

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This study reexamines the traditional use of the 30th highest hourly volume as the optimum design hour volume given the current era of limited funding, constrained right-of-way, environmental concerns, and increasing congestion. The report documents the Dallas/Ft. Worth region's use of an alternative design hour volume (4th highest hour of the day) based on funding constraints. The use of an alternative design hour volume requires that the planned system be optimized to manage peak person trip flows by identifying the best mix of general purpose, high occupancy and express lanes, and an aggressive program of transportation system management and demand management strategies A methodology is outlined to use a peak hour traffic model to forecast traffic volumes for different hours of the day. This approach has the potential to avoid some of the shortcomings of using average values for peak hour factors, directional split, and trucks to obtain hourly design volumes from daily forecasts. If congestion is accepted during the peak hours of the day, then the design process for a facility must expressly consider congested conditions. Nine design elements that pose operational/safety concerns were examined under congested conditions to identify basic guidelines that should be considered when designing for congestion.