Assessment of vehicle speeds on different categories of roadways in Ghana.

Empirical evidence from road safety literature suggests that vehicular speed is an important risk factor in the incidence and severity of road traffic crashes globally. Speed studies are at rudimentary stages in developing countries, thus making vehicular speed research imperative. The main aim of the study was to establish two major speed parameters, namely, the mean and dispersion, and their implications for more extensive and long-term speed monitoring in Ghana. Research workers stationed themselves in a parked car and used a radar gun to unobtrusively measure the travelling speeds of 28,489 vehicles at 15 different inter-urban locations on three highway categories. Excessive speeding is very pervasive on all highway categories in Ghana. Travelling speeds through settlements where a speed limit of 50 km/hour is mandatory were particularly excessive. Generally, 98%, 90% and 97% of vehicles exceeded the posted speed limit of 50 km/hour on national, inter-regional and regional roads respectively. Mean speeds and speed dispersions (as assessed by the standard deviations) through built-up areas were 81.3 +/- 17.3 km/hour on national roads, 64.7 +/- 12.3 km/hour on inter-regional roads and 72.6 +/- 13.4, km/hour on regional roads. On rural undivided highways with an 80 km/hour speed limit, mean and speed dispersions were 90 +/- 18.9 km/hour on national roads, 80.1 +/- 16 km/hour on inter-regional roads and 84.4 +/- 15.6 on regional roads; also translating into 66%, 47% and 60% of vehicles exceeding recommended speeds. In all cases, speed dispersions were notably higher than the value of 10 km/hour generally found in developed countries. Excessive speeding and wide speed dispersions are highly prevalent on Ghana's highways. These factors likely account for the high incidence of traffic crashes and fatalities in Ghana. An integrated speed monitoring and control programme and by-passing small and medium settlements would be required for the reduction of speed-related crashes, fatalities and injuries.