Saint Paul, Minnesota, metropolitan area and showed that adverse weather causes clear reductions in traffic speed: up to 6% for rain, 13% for snow, and 12% for reduced visibility (1). Ibrahim and Hall (5) analyzed the effects of adverse weather on the speed-flow and flow-occupancy relationships for Canadian travelers and found the effects of snow to be much larger than those of rain and to cause a reduction in free-flow speed of 38 to 50 km/h. The effects of weather on traffic volume are also evident from empirical data. The research conducted by Datla and Sharma indicates that the impact of cold and snow on traffic volume varies with the type of trip and hour of the day (6). From traffic data collected in Canada, they observed that commute trips experience the lowest reductions in volume because of snowy weather, of up to 14%, while recreational trips experience the highest reductions, of up to 31%. They also found that reductions in commute trips during off-peak hours (−10% to −15%) were generally greater than those during peak hours (−6% to −10%); however, an opposite pattern was observed for recreational trips. All these studies show that inclement weather may have a significant and comprehensive impact on the transportation system that cannot be ignored by planners and decision makers.To mitigate the impacts of adverse weather on highway travel, the FHWA Road Weather Management Program has been involved in research, development, and deployment of strategies and tools for weather-responsive traffic management. In a project completed in 2006, the Road Weather Management Program used data from Seattle, Washington; Minneapolis, Minnesota; and Baltimore, Maryland; to develop statistical models and adjustment factors to quantify the impacts of weather on traffic flow (7). One of the challenges remaining is to integrate those models into decision support systems to help improve the performance of the transportation system during inclement weather conditions. The traffic estimation and prediction system (TrEPS) is a tool currently available for traffic planners and operators to assist with evaluating and implementing weatherresponsive traffic management strategies. Weather-sensitive TrEPS capabilities aim for accurate estimation and prediction of the traffic states under inclement weather conditions. Mahmassani et al. identified several key components within the TrEPS framework for which the impact of weather must be incorporated on both the supply and demand sides (8). One such element on the supply side consists of well-calibrated weather-integrated traffic flow models. Successful application of weather-sensitive TrEPS requires detailed calibration of weather effects on the underlying traffic flow models.The main objectives of this paper are (a) to develop systematic procedures for calibrating traffic flow models under inclement Calibration of Traffic Flow Models Under Adverse Weather and Application in Mesoscopic Network SimulationTian Hou, Hani S. Mahmassani, Roemer M. Alfelor, Jiwon Kim, and Meead SaberiThe we...

Gage restraint is an important indicator of track condition and safety. In 1999, approximately 13 percent of derailments were caused by reductions in gage restraint and the resulting widening of the track gage. Existing techniques for the measurement of gage restraint allow identification of track sections with weak lateral support. However, little has been done to investigate the change in, or weakening of, gage restraint over time as a function of track, traffic, and environmental parameters. A track degradation assessment study is under way to develop models that can be used to predict changes in gage restraint by using data obtained from the automated Gage Restraint Measurement System. The degradation models will be useful for forecasting the future condition of the track, determining the appropriate frequency and timing of track inspections, and evaluating the effectiveness of maintenance strategies. A literature review of track degradation models and previous work on gage restraint analysis is presented. The rationale for adoption of an empirical approach to gage restraint degradation modeling is explained. The processing applied to the automatically collected data and the preliminary database program developed to store the information and estimate track degradation equations are also described. The track degradation analysis and database development study currently focuses on gage restraints and track geometry parameters as measures of condition. In the future, this can be extended to include other degradation parameters for a comprehensive track performance analysis.

information into their operations to support the operational decisions about various WRTM strategies (4). There have been active efforts in states around the country to develop and implement a wide range of advisory, control, and treatment strategies under the framework of WRTM. A comprehensive overview of WRTM practices and a collection of case studies from municipal and state transportation agencies can be found in Gopalakrishna et al. (5) and Murphy et al. (6), respectively. Also there have been efforts to integrate the weather effects into decision support tools allowing improved traffic state prediction and estimation (7,8).To reduce the impacts of inclement weather events and prevent congestion before it occurs, weather-related advisory and control measures could be determined for predicted traffic conditions consistent with the forecast weather, that is, anticipatory road weather information. A recent study identified levels of weather information integration in TMC operations and found that many TMCs viewed the desirable level of decision support strategies as using "response scenarios through software supply potential solutions with projected outcomes," while the current levels were evaluated as "ad hoc implementation of weather management strategies" (4).The goal of this study is to bridge this gap between the state of the practice and state of the art by integrating WRTM and a traffic estimation and prediction system (TrEPS). TrEPS models (9-12) are simulation-based decision support tools that provide predictive information on how traffic behaves in a given network under likely future conditions. In a previous FHWA project (7), a methodology for incorporating weather impacts in TrEPS was developed. The principal supply-side and demand-side elements affected by adverse weather were systematically identified and modeled in the TrEPS framework. The methodology was incorporated and tested in connection with the DYNASMART-P simulation-based dynamic traffic assignment system (13), providing a tool for modeling the effect of adverse weather on traffic system properties and performance and for supporting the analysis and design of traffic management strategies targeted at such conditions. The methodological development conducted to enable weather responsiveness of the simulation tools was further calibrated and validated and integrated in a real-time estimation and prediction capability (14) to support the goal of making WRTM an integral part of the traffic system management (15).On the basis of the weather-sensitive TrEPS developed in the previous studies (7,15), this paper establishes a general framework for incorporating TrEPS in actual TMC operations to support the design, implementation, and evaluation of WRTM strategies suitable The disruptive effect of inclement weather on traffic results in considerable congestion and delay, because of reduced service capacity, diminished reliability of travel, and greater risk of accident involvement. To mitigate the impacts of adverse weather on highway travel, the...