COMPARISON OF UNCONGESTED SPEED-FLOW RELATIONSHIPS USING DATA FROM GERMAN AUTOBAHNS AND NORTH AMERICAN FREEWAYS

The use of speed-flow data from German Autobahns provides a greater range of free-flow speeds than that available from North American freeways. On the basis of these additional data, three conclusions address current questions about the speed-flow relationship. First, the speed at capacity is not independent of free-flow speed but is higher on facilities on which the free-flow speed is higher; speed approaching capacity is as high as 90 to 100 km/hr on one Autobahn. Second, the range of flows over which average speeds remain constant (at the free-flow speed) decreases with increasing free-flow speed. For example, with a free-flow speed of 135 km/hr, speeds remain constant out to flows of 1,000 passenger car units per hour per lane. Third, for the range of flows in which speeds decrease with increasing flow, the relationship between speed and flow appears to be linear. This means that there is no need to postulate a curved (e.g., quadratic) relationship near capacity, since there is not an increasing rate of decline in speeds at those flows.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/trr/1994/1457/1457-004.pdf
• Record URL:
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• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1457, Part 2, Traffic Flow and Capacity. 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
• Authors:
  • Hall, Fred L.
  • Brilon, Werner
• Publication Date: 1994

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 35-42
• Monograph Title: Part 1: 1994 TRB Distinguished Lecture, Adolf D May; Part 2: Traffic flow and capacity
• Serial:
  • Transportation Research Record
  • Issue Number: 1457
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Alternatives analysis; Flow speed relationships; Free flow speeds; Freeways
• Identifier Terms: Autobahn
• Uncontrolled Terms: Speed-flow relationships
• Geographic Terms: Germany; North America
• Old TRIS Terms: Speed at capacity
• Subject Areas: Highways; Operations and Traffic Management; I71: Traffic Theory;

Filing Info

• Accession Number: 00677644
• Record Type: Publication
• ISBN: 0309061008
• Files: TRIS, TRB
• Created Date: May 10 1995 12:00AM