Investigating the relationship between horizontal curve radius and vehicle speed utilised to calculate limiting curve speed

Abstract

There are several factors that affect vehicle speed at curves but the most important have been found to be the Curve radius and the approach velocity of the vehicles. This research focused on determining the coefficients in the regression equation that relates horizontal curve radius to vehicle speed on paved roads in Uganda The Ugandan roads follow existing alignments hence do not have consistent levels of service which is very dangerous for any road network. Research has not been done capturing the effect of approach velocity on curve speed in Uganda hence the necessity for this research. This project investigated the relationship between the horizontal curve radius and vehicle speed which relationship was used to get coefficients that can be utilized to calculate limiting curve speed in Uganda. Curve radii were established from the as built drawings of these roads as provided by UNRA. In order to determine approach velocity, an application called ‘Speed gun’ was used and curve speed was got using stop watches with two people at either end of the curve noting the time of passing of the vehicle hence being able to derive curve speed from curve distance and time to traverse the curve. Using the regression curve VCURVE = a0 + a1Vapp + a2R Where; a0, a1 and a2 are regression coefficients Vappis the approach velocity in m/s R is the radius of the curve in metres, the coefficients needed to calculate the limiting curve speed in Uganda were deduced and are ready to be applied. The behavior of vehicle acceleration, approach velocities and curve speeds in relation to curve radius were also determined. Detours, motorcycle lanes and an allocation of the road budget to the re – alignment of horizontal curves of Ugandan roads were recommended due to the results detailed in this research. Furthermore, a deeper research on the effect of road improvement and re – alignment on vehicle safety with special emphasis on motorcycles was recommended.