Citation

Blumenthal RC, Horn JW. Highw. Res. Board bull. 1957; 167: 42-62.

Copyright

(Copyright © 1957, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Comparison studies are reported on capacities of signalized intersections in the boston metropolitan area compared with results presented in the highway capacity manual. Data from 21 pressurized intersections (intersections where the approach understudy had a continual backlog of waiting vehicles) indicated capacities in excess of those reported in the manual. Volumes on approaches average 14% higher than manual averages. A much higher capacity potential, especially in the wider street width, is indicated under pressurized conditions which motorists are currently tolerating in larger metropolitan areas. The factor found locally to have the greatest influence on the capacities was the turning movement. Left turns appear to have a greater initial effect under pressurized conditions than the manual indicates. Local data indicates that when left-turning volumes are equal to or greater than 50% of the total approach, they operate as through traffic with little reductive effort. The effect of commercial vehicles was found consistent with that proposed by the manual. Data indicate a greater effect due to the presence of commercial vehicles when they make up more than 20% of the total approach volume. The study indicates that the reductive effect of the opposing left turn is sufficient to be evaluated alongside the usual lefts, rights, and commercial percentages.