This paper examines the implications of climate change on cross slope with respect to geometric design and road safety. The importance of risk to the highway infrastructure due to climate change has been recognized nationally by the Public Infrastructure Engineering Vulnerability Committee (PIEVC) Engineering Protocol and internationally by the ISO 31000 Risk Management standard. Uncertainty in infrastructure design is outlined in the ASCE Manual of Practice No. 140-Climate -Resilient Infrastructure Adaptive Design and Risk Management (2018). In Canada BCMoTI is developing climate change-resilient designs for highway infrastructure in British Columbia. Examples of climate change parameters typically used in highway design include rainfall, temperature, snow, wind, sea level and water flow. This paper focuses on rainfall and whether current design standards for cross slope will provide sufficient drainage from a road safety perspective.
The TAC 2017 Geometric Design Guide for Canadian Roads notes that “the normal cross slope of 0.02m/m on paved tangent roadways provides positive drainage to the curbs.” As well the TAC Guide acknowledges that “some Canadian road agencies use a cross slope of 0.03m/m on paved tangent sections to reduce the risk of Hydroplaning.” One of these agencies is the New Brunswick Department of Transportation and Infrastructure (NBDTI) and this paper discusses their experience with a cross slope of 0.03m/m in terms of operations and safety.
The paper includes a global review of cross slope design practice and cross slope research with respect to hydroplaning. For example, the Austroads Guide to Road Design Part 3 Geometric Design (2013) states “crossfalls flatter than 2% do not drain adequately, and even 2% should only be prescribed for concrete pavements where levels and surface finish are tightly controlled. Unless compaction and surface shape are well controlled during construction, pavements with less than 2.5% crossfall will hold small ponds on the surface, which cause potholes to develop and hasten pavement failure. Rutting of the pavements is also more likely to hold water, increasing the risk of pavement deterioration and vehicle aquaplaning when the pavement crossfall is less than 3%”. In a report by John C. Glennon (2006), Roadway Hydroplaning-The Trouble with Highway Cross Slope, states that “based on research findings and in consideration of pavement irregularities (settlements, wheel ruts, etc) that seem all too common, AASHTO should consider recommending 2-2.5% minimum cross slopes to minimize the propensity for hydroplaning particularly for high-speed highways. This paper concludes with a recommendation that TAC should undertake a research project to determine the most appropriate cross slope that mitigates the impact of climate change on drainage related safety concerns.