This report details a framework for rationally arriving at economically justifiable operating speed reductions to compensate for the inability to achieve recommended levels of skid resistance on high-risk curves. The framework is based on vehicle speed-related procedures incorporated in the Transport Agency’s Economic evaluation manual. These procedures include travel time, vehicle operating costs, carbon dioxide emissions and crash severity. Relationships between the skid resistance level of the road surface and curve crash risk and expected service life of the road surface derived from previous New Zealand specific research are also employed.
The framework was trialled on a 10 km section of state highway 58 with a 100 km/h speed limit. A decrease in operational speed of only 10 km/h was found to be sufficient to completely negate the increased curve crash risk that results when the skid resistance of the high crash risk curves is managed to a lower level of 0.4 ESC rather than the recommended investigatory level. The overall benefit of reducing the 100 km/h speed limit by 10 km/h amounted to an annual cost saving of about $1.5 million, with the reduction in speed change cycle costs making the largest contribution.
Keywords: crash risk, economic evaluation, operating speed, skid resistance investigatory levels, speed limit setting