Knowledge Resources

To address weather related crashes on a section of Interstate 90 near Vantage, Washington; the Washington State Department of Transportation (WSDOT) assessed the benefits and costs of deploying an automated anti-icing system to prevent the formation of pavement frost and black ice and to reduce the impact of freezing rain. Poor road surface conditions contributed to 42 percent of total crashes and 70 percent of winter crashes. The high crash corridor extends from milepost 137.67 (the Columbia River Bridge approach) to milepost 138.49, near the State Route 26 Interchange. This corridor includes a 955-foot radius horizontal curve and a vertical alignment transition from three to five percent within the limits of the curve. The average daily traffic volume on this road section is 10,000 vehicles per day with 26 percent trucks.

The system design included a liquid chemical storage tank, a pump, a 3,100-foot dispensing system with barrier-mounted and pavement-embedded spray nozzles, an environmental sensor station (ESS), a computerized control system, and a closed circuit television (CCTV) camera for remote viewing. The control system monitors weather and road condition data from the ESS and automatically activates the dispensing system when predetermined conditions exist. The system also alerts dispatchers and the North Central Region maintenance supervisor when the anti-icing system is activated.

FINDINGS

The present worth of costs, the present worth of benefits and the benefit-to-cost ratio were calculated with WSDOT’s Benefit/Cost Worksheet for Collision Reduction. Cost elements included design, construction, power and communication, operations and maintenance costs. Benefits were the estimated reduction in snow, ice, and wet pavement crashes. Using historical crash data, the annual rate of collisions over a three-year period was determined and compared to the expected rate of collisions after system implementation. It was estimated that 80 percent of the snow, ice, and wet pavement crashes would be eliminated (see key assumptions in notes below). The cost per collision was used to determine the annual safety benefit. The analysis resulted in a benefit-to-cost ratio of 2.36:1 with a net benefit of $1,179,274. This ratio validated the viability of the proposed solution. In addition to cost savings from crash reductions, WSDOT management expects that abrasive usage will be significantly reduced, resulting in lower cleanup costs and less damage to drainage structures. Improved level of service should also result from the deployment, enhancing mobility.

Notes

Initially, it was estimated that 60 percent of snow and ice crashes would be eliminated by the proposed system, with no reduction in wet-pavement crashes. Based upon discussions with Pennsylvania DOT maintenance managers, this estimate was revised to 80 percent of snow and ice crashes.