00675335

Component

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

https://scholar.google.co...chez&publication_year=1994

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.

This paper appears in Transportation Research Record No. 1445, Cross Section and Alinement Design Issues. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved

01401257

English

p. 101-108

1994

Transportation Research Record

0309060516

Figures (4) ; References (10) ; Tables (4)

Alignment; Computer aided design; Geometric design; Highway design; Interchanges; Interchanges and intersections; Slopes; Stopping sight distance

Cross slope; Horizontal alignment; Longitudinal barriers; Three dimensional analysis; Vertical alignment

Design; Highways; I20: Design and Planning of Transport Infrastructure

TRIS, TRB, ATRI

Mar 20 1995 12:00AM

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