Development of Winter Maintenance Demand and Performance Indices

Transportation agencies are often asked to quantify the severity of a winter storm or season. An objective characterization of severity can help agencies judge whether the cost and effort of their maintenance responses are commensurate to the maintenance need imposed by winter conditions. Objective characterization is essential to agencies' long-term efforts to evaluate and improve their effectiveness and efficiency. Several distinct approaches have been attempted. The first calculates a winter severity index based upon weather conditions such as temperature, precipitation, and wind, either alone or in combination with each other. Although such indices describe weather, they do not reliably describe the effect of weather on road conditions and the need for winter maintenance. For instance, they may not account for situations where more demanding maintenance needs exist at temperatures near freezing than at colder temperatures. Other approaches try to portray the impact of weather conditions on maintenance demands by calculating an index as a weighted combination of specific weather events or conditions. Weights are chosen on the basis of relative impact, as determined from expert opinion or statistical methods. A freezing rain event, for example, might be weighted more strongly than snowfall at colder temperatures. A more recent approach employs an automated Maintenance Decision Support System (MDSS) to objectively independently estimate the maintenance demand created by winter events or seasons. By simulating the accumulation of snow and ice on pavement surfaces and the effect of applied maintenance treatments, the MDSS estimates the amount of effort and expense necessary to achieve or maintain a defined level of service on the roadway. An estimate based on standard treatment capabilities and levels of service could constitute a baseline for comparison to actual or other potential maintenance strategies. Regardless of the approach employed, practitioners have found it difficult to develop indices that are transferable across geographic and temporal domains. In many cases, different definitions have been needed among different regions even within single states. Likewise, approaches involving subjective perceptions have lacked the temporal stability necessary to gage long-term performance. The utility of some indices to support agencies' business decisions has also been limited. The South Dakota Department of Transportation (SDDOT) has not historically calculated or used an index to characterize winter severity or maintenance demand. However, the recent combination of customer expectations, fiscal pressure, and newly available technology has led SDDOT to adopt new winter maintenance approaches and to seek a means to evaluate their effectiveness. Research is needed to identify and evaluate potential methods for characterizing winter maintenance demand and for assessing the efficiency and effectiveness of SDDOT's maintenance activities. The objectives of this project are to: (1)  identify candidate indices for characterizing the severity or maintenance demand of winter storms and seasons and the effectiveness of maintenance responses; (2)  demonstrate and evaluate candidate indices through use of available historical data and data collected during the winter of 2010-2011; and ( 3) recommend winter severity or maintenance demand indices along with methodology for their application to support SDDOT business decisions. Research tasks of the project are as follows. (1) Meet with the project's technical panel to review project scope and work plan. (2) Through a literature review and interviews with transportation officials, identify practices recently and currently employed by state and local transportation agencies to quantify winter severity and maintenance demand. (3) Through interviews with selected supervisors and managers in SDDOT, identify business purposes for which calculated indices will be applied. (4) Prepare and present to the project's technical panel a technical memorandum that describes and evaluates candidate indices on the basis of objectivity, data availability and cost, geographical applicability, temporal stability, and ability to support business decisions. (5) Upon direction of the project's technical panel, analyze available historical data to demonstrate the behavior of candidate indices in recent winters. (6) Establish and execute procedures for tracking candidate indices and demonstrating their application in one Area Office within each of SDDOT's four geographic Regions during the winter of 2010-2011. (7) Midway through the winter of 2010-2011, prepare and present to the project's technical panel a technical memorandum summarizing the historical analysis and a partial analysis of 2010-2011 winter. (8) On the basis of the evaluation of historical data and data obtained during the entire winter of 2010-2011, recommend preferred indices for characterizing the severity or maintenance demand of winter storms and seasons and the effectiveness of maintenance responses. (9) Prepare a final report summarizing the research methodology, findings, conclusions and recommendations. (10) Make an executive presentation to SDDOT's Research Review Board at the conclusion of the project.