The acceleration of light vehicles

Abstract

Paper presented at the 32nd Annual Southern African Transport Conference 8-11 July 2013 "Transport and Sustainable Infrastructure", CSIR International Convention Centre, Pretoria, South Africa.

The acceleration of light vehicles is often seen as an indicator of driver aggression. In automotive advertising the number of seconds it takes to reach a speed of 100 km/h can be a major selling point for certain types of vehicle. The development of representative and reliable speed profiles for vehicles accelerating from a stationary position, for vehicles overtaking slower vehicles from a reduced speed and for vehicles exiting a horizontal curve are important parameters for engineers involved with the design and/or appraisal of the safety of roads. Importantly, this paper only deals with vehicles accelerating from a stationary position to speeds of 60 and 100 km/h. Most drivers of light vehicles do not utilise the maximum power available to them when accelerating a vehicle. The purpose of a recent study (Grobler, 2012) was to determine the proportion of the maximum acceleration that drivers are using when accelerating their vehicle within an urban environment. In this study a limited number of drivers and vehicles were used to determine their acceleration from a stationary position. Since acceleration is decreasing from a maximum value with an increase in speed up to a point where the maximum speed of the vehicle is reached (Papacostas et al, 2005), it was necessary to calibrate a model for each test. The results showed that drivers on average used about 55% of the maximum acceleration available to them. This average and the distribution can be used in speed profile calculation and programs that simulate the acceleration of vehicles. From the percentage of individual drivers it was also possible to categorise the drivers into three different groups, namely standard, gradual and hard accelerators, which may be an indicator of driver aggression.