Is road infrastructure that improves operating speed a double-edged sword when it comes to road safety?

Building new or upgrading existing road infrastructure is a common practice to reduce congestion and improve travel time. Road infrastructure projects that successfully improve operating speeds throughout the day or just during peak periods also have an impact on safety. This paper aims to address how new or upgraded road infrastructure primarily constructed to improve operating speed impacts road safety. Is road safety improved, worsened or negligibly changed? Literature indicates that higher speeds increase the severity of road accidents but new and upgraded road infrastructure is generally built to a standard that will reduce the probability of accidents occurring. Does the reduced probability of an accident occurring offset the more severe accidents likely to occur from the higher operating speeds? The matter is further complicated when the new or upgraded infrastructure eliminates particular severe accident types that occur even at lower speeds such as head-on collisions on existing single carriageway roads. In this paper, three types of road projects are considered, town bypasses, duplication of carriageways and overtaking lanes. These three types of projects have been selected due to the different nature of safety implications for each project type. The accident costs for each of these projects have been calculated using both the Austroadsr human capital approach and Hensherrs willingness to pay approach. Reductions in accidents are calculated based on model road state (MRS) and percentage reductions based on particular treatments. The safety implications for projects may not be as predictable as one would expect.