Average Speed Enforcement (ASE) is an emergent alternative to instantaneous speed limit enforcement to improve road safety, and is used to enforce an average speed limit over a road segment. This paper presents a study on the response of passenger vehicles and minibus taxis to ASE on the R61 in South Africa. A spatio-temporal quantitative study of speed compliance is conducted, where metrics such as speed variability, average speed and 85th percentile speed measured prior to, and during enforcement are analysed for two prominent modes of transport – passenger vehicles and minibus taxis. These measurements are taken on the enforcement route and on control routes adjacent to and further away from the enforcement route. A qualitative study is also conducted to evaluate the relationship between speed compliance and driver understanding of the system. The impact of the system on crash risk and injury severity is also examined before and during enforcement. For passenger vehicles, results show that the introduction of ASE was followed by a reduction in mean speed on the enforcement route and adjacent control route. For minibus taxis, it was found that ASE appears to have little influence on improving speed compliance, which is likely associated with a lack of driver understanding on how the system operates.

Informal transport refers to the collective passengerroad transport industry with little or no regulatory control of its operations, usually characterised by unplanned and ad-hoc service delivery. The notoriously dangerous informal transport industry in South Africa – dominated by minibus taxis – has been shown to disregard the posted speed limit on long-distance trips. Not only do they frequently exceed the differentiated speed limit imposed on minibus taxis, but also the speed limit imposed on normal passenger vehicles. This paper evaluates the impact of an auditory Intelligent Speed Adaptation (ISA) intervention, applied at various intensity levels, on the speeding behaviour of this seemingly intransigent mode of transport. The experiment evaluates the behaviour on the R61 between Beaufort West and Aberdeen. We evaluate the speeding distributions, speeding frequencies, speed percentiles, mean speeds, and the statistical relevance of key metrics. We find that the auditory intervention has a clear impact on speeding behaviour, both when appliedat an audible level that can be drowned out by a radio, andeven greater impact at a loud level. The impact on speedingis significant, with speeding frequency (both time and distance) reducing by over 20 percentage points.