Incorporating Weather Impacts in Traffic Estimation and Prediction Systems

Dr. Mahmassani served as PI for this study conducted for FHWA under a subcontract to SAIC, Inc. The objectives of the project are to develop weather-sensitive traffic prediction and estimation models and incorporate them in existing traffic estimation and prediction systems. This includes enhancement of the capabilities in mesoscopic DTA tools to model traffic behavior under inclement weather, and capture user responses to inclement weather with and without the presence of advisory and control strategies.

As a result of this project, The DYNASMART TrEPS can now capture the effects of adverse weather on traffic patterns through both supply and demand side modifications to the model. New weather‐related features in DYNASMART include:

Weather Scenario Specification. DYNASMART allows users to specify various weather scenarios for the study network. It can be represented as either the network-wide weather condition or the link‐specific weather condition.

Weather Adjustment Factor.  Users can define the effect of weather on supply‐side traffic parameters such as free flow speed and capacity based on three weather condition parameters: visibility (mile), rain precipitation intensity (inch/hr) and snow precipitation intensity (inch/hr) by means of Weather Adjustment Factors (WAF). DYNASMART applies user‐specified WAF to 18 supply‐side traffic properties for links within the impacted region to simulate traffic conditions under the weather condition. WAF can be obtained based on calibrated weather‐traffic flow relation.

Modeling Traffic Advisory and Control via Variable Message Signs (VMS) DYNASMART provides three weather‐related VMS operation functionalities : (1) Speed Reduction Warning – via a VMS warning sign indicating low visibility (e.g., fog) or slippery road (e.g. rain and snow), speed reduction behavior under adverse weather can be simulated; (2) Optional Detour – VMS suggests that travelers re-evaluate their current route based on the generalized cost that includes travel penalties of the added delays caused by adverse weather; and (3) Variable Speed Limit (VSL) – in DYNASMART, vehicle speed can be regulated through the speed limits posted on VMS in correspondence with prevailing weather conditions.