Citation

Sanchez E. Transp. Res. Rec. 1994; 1445: 101-108.

Copyright

(Copyright © 1994, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

The design of interchange ramps and connectors, especially in large freeway-to-freeway interchanges, involves the use of stopping sight distance (SSD) criteria to determine horizontal and vertical geometries. Long connectors are usually required to avoid difficult horizontal and vertical obstructions. Therefore the use of minimum design standards for both horizontal and vertical geometries is quite common. The results of an investigation that evaluated SSD on interchange connectors by computerized three-dimensional (3-D) models are documented. Interchange connector models were developed by using combinations of minimal horizontal and vertical geometries with a longitudinal traffic barrier and a cross slope. A graphical procedure was used to measure SSD in a 3-D environment. The results revealed that the 3-D method of measuring SSD was not significantly different from the conventional two-dimensional method of measuring SSD. When all the 3-D models were rotated and viewed from different angles, the line of sight was always obstructed by the longitudinal barrier. Driver perspective views revealed that the cross slope affected the available SSD significantly. Therefore when a vertical curve is combined with a horizontal curve that requires a cross slope, the line of sight is not blocked by the roadway surface. This observation indicates an additional conservatism in the current crest vertical curve methodology. Designers should consider using computerized 3-D models in their normal design procedures. The use of models will allow designers to view different geometric configurations before deciding on the final combination. The models will allow designers to see the end result before the actual construction begins and thereby possibly eliminate costly field alterations.

Record URL:
http://onlinepubs.trb.org/Onlinepubs/trr/1994/1445/1445-011.pdf

Language: en

Keywords

Speed; Traffic signals; Visibility; Standards; Alignment; Computer simulation; Graph theory; Curves (road); Interchanges; Geometry; Transportation personnel; Structural design