Review of Speed and road crashes relationship in low-and -middle-income countries. Do the power and exponential model hold?

Low-and-middle income countries (LMICs) continue to suffer the negative consequences of crashes with speed recognised as the main causative factor. The relationship between speed and crash outcome is complex and has been subject to debate. Over the years, how speed affects the outcome of a crash has been investigated amongst researchers and argued to depend on the type of traffic environment which has led to the re-analysis and development of models for different road environments. However, the literature neglects the effects of mixed traffic on speed and crashes, and this has raised questions on the applicability of the conventional power and exponential models. This study reviews the literature on speed and crashes in mixed traffic, for LMICs, and verifies the applicability of the power models to the context. Study results indicate that speed studies in LMICs are rudimentary and while studies support the positive relationship between speed, speed variance, and crashes, the strength of the relationship is unknown. Literature provides no conclusive evidence on the applicability of the power and exponential models to LMICs roads, and this remains controversial. More research efforts in LMICs should focus on the effects of speed, impact speed and speed variance on crashes both at the aggregated and individual road user levels.