Design guidelines for horizontal reverse curves combined with vertical alignments
Horizontal reverse curves are used in all types of highways either in highway mainlines or in highway interchange ramps. The main advantage of horizontal reverse curves is that they are economical because their need for space is minimal. When a vehicle travels along any horizontal curve, it experiences centrifugal force outward the centre of the curve. This centrifugal force is inversely proportional to the radius of the curve, as it increases with the decrease in the radius of the horizontal curve. Vehicle stability is achieved by the forces that resist the centrifugal force. These resistive forces include frictional interaction between the tires and pavement, and a component of the vehicle weight that acts parallel to the road surface. The component of the vehicle weight that acts parallel to the road surface depends on the side slope of the highway, which is usually referred to as superelevation. At present there are no design guidelines for the design of horizontal reverse curves. This paper establishes such guidelines using computer software that simulates vehicle behaviour on different geometric alignments based on vehicle stability. It was found that for a flat reverse horizontal curve (without being superimposed by any vertical alignment), the critical speed where a truck starts to rollover was as low as 10 Km/h above the design speed. The critical speed decreases to be as low as 6 km/h above the design speed when the reverse curve is superimposed by a sag vertical curve. This is a particular concern for freeway ramps, where horizontal reverse curves combined with vertical alignments are commonly used. Noting that many ramps have unrealistically low design speeds in comparison with the design speed of the mainline roadway, safety problems may be encountered due to driver behaviour to overdrive ramps if their design speeds were not appropriately selected. The established design guidelines for horizontal reverse curves should be useful in improving road safety on highways, especially at freeway interchanges.
|Conference||Canadian Society for Civil Engineering - 31st Annual Conference: 2003 Building our Civilization|
Dabbour, E. (Essam), Easa, S. (Said), & Halim, A.O. (2003). Design guidelines for horizontal reverse curves combined with vertical alignments. In Proceedings, Annual Conference - Canadian Society for Civil Engineering (pp. 1662–1671).