Citation

Parsonson PS, Day RA, Gawlas JA, Black GW. Transp. Res. Rec. 1979; 737: 17-23.

Copyright

(Copyright © 1979, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

This paper describes a new detector-controller configuration intended to minimize the dilemma-zone problem at signalized intersections on high-speed roads. Included are a complete functional and electrical description of the design, the findings of a field test, and a comparison with two existing designs. The new design uses a basic, actuated, digital controller operated in the nonlocking mode. An approach that has a design speed of 89 km.h (55 mph) has an upstream detection loop located 117 m (384 ft) back from the intersection and a middle loop 77 m (254 ft) back. A loop at the stopline is 8 m (25 ft) in length and is connected to a novel extended-call--delayed-call (EC-DC) detector that is able to change from an EC model to a DC unit at the strategic moment during the green interval. In effect, the change disconnects the stopline loop, leaving the other two loops to control the extension and termination of the green. The controller and detectors are off-the-shelf units that require no internal modification. The only special-logic items are two relays mounted on the back panel. The design does not pose a maintenance problem. A test installation in Georgia significantly reduced conflicts associated with the dilemma zone. A comparison with two existing designs shows that the EC-DC configuration costs somewhat more than the EC design but is superior in three operational categories. It is less expensive than the density design and is superior in four operational aspects.