Abstract:
In recent years, Sri Lanka has experienced an urban traffic congestion that caused a waste of time and
energy. It is known that road geometries partly contribute towards decrease in operating vehicle
speed. According to conventional Highway Geometric design procedure there is no accurate method to
predict operating vehicle speed with different combinations of horizontal alignment (variation of
bends with respect to different curvatures). This study explores a methodology to evaluate the actual
horizontal alignment of roads to increase the efficiency of highway management with respect to
reducing travel time.
In this paper after classification of all the design elements, the new concept of “curvature Index” (the
degree of angle variation per unit length) is introduced to represent actual horizontal alignment of a
road segment including number of bends and nature of bends. The curvature index measures analyzed
were : bend density (number of bends per km); cumulative angle (degrees per km); mean angle
(degrees); and standard deviation of angles. The research confirmed that driver's speed choices are
more strongly related to curvature Index than curve design speed, and to the approach speed
environment.
The curvature index and operating vehicle speed is estimated using the database of GPS (Global
Positioning System) receivers. GPS data is collected at selected road segments in Sri Lanka closely
representing free flow condition. A methodology is developed to increase the reliability of GPS data
obtained in order to investigate the relationship between curvature indexes and operating vehicle
speed. Simple linear regression analysis is used to develop operating vehicle speed models, which
related driver speed to the curvature Index of the highway. ArcGIS (Geographical Information System)
provides a good platform to model relationship between curvature index and operating vehicle speed
because the analysis tools in GIS can be directly used to analyze the GPS data.
Citation:
Rajapaksha, R.P.G.K.S., & Bandara, J.M.S.J. (2011). An approach to evaluate horizontal alignment of highways using curvature index and operating vehicle speed [Abstract]. In H.R. Pasindu (Ed.), Proceedings of the Transportation Research Forum 2011 (p. 25). Department of Civil Engineering, University of Moratuwa. https://uom.lk/sites/default/files/civil/files/TRF%202011_0.pdf