Guidelines for Ramp Terminal Spacing for Freeways
Author(s):
K. Fitzpatrick, R.J. Porter, G. Pesti, C. Chu, E. Park, T.Q. Le
Publication Date:
December 2009
Abstract:
Existing geometric design guidance related to interchange ramp spacing in the Texas Roadway Design Manual and the American Association of State and Highway Officials' A Policy on Geometric Design of Highways and Streets is not speed dependent even though intuition indicates spacing and speed are related. The objectives of this project were to investigate relationships between weaving length, speed, and overall vehicle operations on Texas freeways; and to propose updates to current Texas Department of Transportation (TxDOT) guidance on recommended distances between ramps. Historically, the minimum weaving length with an auxiliary lane has been 1500 feet. The literature on safety identifies trends that indicate longer spacing is associated with fewer crashes. Values identified from the evaluation of the field data collected in this study along with values calculated using minimum acceleration and deceleration values were suggested as spacing dimensions. Also suggested for consideration by TxDOT is a weaving length based on preliminary findings from safety investigations along with the value being used in England for rural motorways. The main product of this research was new material for consideration in ramp spacing.
Report Number:
0-5860-S
Electronic Link(s):
Document/Product
http://library.ctr.utexas.edu/hostedpdfs/txdot/psr/5860.pdf
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