Weather presents considerable challenges to highway agencies both in terms of safety and operations. State transportation agencies have developed road weather information systems (RWIS) to address such challenges. Road weather information has been used by highway agencies in many applications, the primary being for winter maintenance, but also for traveler information, and weather-related intelligent transportation system (ITS) applications. The Montana Department of Transportation (MDT) currently has 73 RWIS stations throughout the state that have been used as a major source of weather data for transportation applications. This project was undertaken to perform a comprehensive review and assessment of MDT’s RWIS program to ensure the efficient use of weather data in various transportation applications and the optimum use of MDT resources. Six major project tasks were completed for this project including a state of the art review, a state of the practice review, a Montana RWIS needs assessment, a weather data and software analysis, a benefit cost analysis, and the development of a site prioritization model. The state of the art review covered literature related to the history and use of RWIS, RWIS data adequacy and reliability knowledge in terms of different sensor and hardware technologies, site selection and geographic coverage practices, and preliminary benefit-cost findings from prior analyses. The review found that RWIS programs have expanded and evolved since their initial primary focus of winter maintenance support to include other uses like traveler information, operations activities, advanced ITS applications, and third-party weather service providers. RWIS technologies were found to be available from many vendors and manufacturers, and agencies are beginning to desire and require open architecture and flexible systems to allow for the use of technologies from more than a single provider. Traditionally environmental sensor stations (ESS) siting was a subjective process relying solely on personal judgement, and some agencies are starting to define systematic, objective ESS placement methods that attempt to quantify and optimize the knowledge held by agency personnel. Optimization models were found to be using data related to winter crash history, traffic volumes, and historical climate data. Overall the literature suggests RWIS programs produce many benefits that outweigh the costs; agency specific benefits like labor, materials, and equipment cost savings have benefit-cost ratios ranging from 1.1:1 up to 11:1, and when safety, operational, and other societal benefits are also considered the benefit-cost ratios increase and can exceed 40:1. The state of the practice review focused on RWIS use, management, and planning and used a survey tool to solicit input from transportation agencies of all 50 States, Washington D.C., Puerto Rico, and the Canadian Provinces. Twenty-eight respondents completed the survey representing 24 states and 2 Canadian Provinces. Similar to the state of the art review, this survey found that RWIS data are being used for purposes including weather-responsive ITS and tracking weather-related performance metrics, but remain primarily focused on winter maintenance support. Operational data like traffic speeds, traffic volumes, and vehicle classifications, are not widely collected at most agencies’ RWIS sites, but a couple of agencies do collect operational data at most/all RWIS locations. A few agencies have begun utilizing mobile RWIS as “non-trivial” portions of their program, and many others have begun to experiment with or use limited mobile RWIS equipment. Current funding and effort levels toward mobile RWIS remain low overall compared to traditional RWIS, but are anticipated to increase in the next five years. Many agencies collect mobile maintenance vehicle data (i.e. plow data, spreader data, Canbus data), but only a few integrate that into their larger RWIS efforts. RWIS site placement is most commonly determined using agency personnel expertise, but some examples of other methods were cited including the use of geo-spatial analyses considering crash histories, climate histories, and traffic levels / road classifications as well as using public input, academic and consultant research, and thermal mapping analysis. Certain RWIS data types were thought to be almost unanimously essential including: pavement temperature, air temperature, pavement condition, wind speed and direction, and precipitation occurrence. Other data types that were thought to be at least helpful on average include: precipitation intensity/depth, humidity, precipitation type, visibility, still camera images, freeze temperature, chemical presence, friction, barometric pressure, and chemical concentration. Non-proprietary RWIS controllers and communications are now required for five of the responding agencies and desired in another eleven. Overall RWIS programs are still expanding with most agencies adding more sites for additional geographic coverage, many agencies enhancing existing locations with additional sensors, and some agencies adding mobile RWIS. In general, most agencies support the idea that more RWIS stations with fewer sensors (i.e. camera and pavement temperature only) would be better than fewer sites with their current configurations if made possible by cost savings using fewer sensors per site. Agency developed, custom software and Vaisala products are the most common software for displaying RWIS data for the responding agencies, but Delcan and Lufft were also cited. Typically RWIS software and hardware are operated and maintained either by agency personnel, Vaisala, or a combination of the two; other vendors (Lufft, Delcan and Narwhal Group) also perform these functions in a few responding agencies. Responses to open ended feedback found many respondents emphasizing the need for RWIS data display software on mobile devices, and improvements in using more mobile RWIS, non-invasive sensor technology, and non-proprietary systems. A needs assessment for RWIS users was conducted using questionnaires and interviews with key MDT personnel to understand their weather information needs. Stakeholder groups included the primary users, winter maintenance personnel, and secondary users from traveler information and aeronautics. Maintenance personnel were found to need camera images, pavement conditions, air temperature, pavement temperature, wind speed and direction, precipitation type and occurrence, and visibility. All stakeholder groups generally favor the idea of having more sites with only a camera and pavement temperature sensor compared to fewer sites with more sensors per site. Maintenance personnel may also need wind sensors or visibility sensors at certain locations. It may be beneficial to update camera images and RWIS data every 15 minutes. The most problematic pieces of equipment from a maintenance perspective, the pan-tilt-zoom (PTZ) cameras, are also the most valuable. Cellular communications are the main source of RWIS data outages and those outages are out of MDT’s control. There are certain sensor and camera technologies that may be desired including non-invasive sensors, more robust precipitation sensors, visibility sensors, live video, and cameras with the ability to produce images in the dark. The ability to display RWIS data for maintenance personnel on mobile devices is desired, but may be partially available currently via the traveler information mobile app. More RWIS sites are desired overall and especially near maintenance section boundaries. Mobile RWIS are not generally desired at the section supervisor / maintenance superintendent level, but more interest is shown at the maintenance chief level. Required RWIS software and server upgrades have recently resulted in some specific functionality losses, namely those related to condition and status alerts. RWIS data is widely used by the public via the traveler information systems from MDT. The public (via traveler information) may be the most common method for the agency to learn of unavailable or malfunctioning sensors and sites. Cameras are the most popular type of information for the public who would presumably prefer more camera-only sites compared to fewer fully-instrumented sites. RWIS is a secondary data source for the Aeronautics Division and general aviation uses in Montana, and camera images with horizon views may be the most valuable RWIS information for aviation. A detailed weather data and software analysis was conducted and provides an overview of the current MDT RWIS system. It also identifies gaps in the current system compared to the needs of the agency, and identifies and analyzes potential hardware and software alternatives that may best meet the needs of the agency. MDT’s RWIS program currently includes 73 ESS providing data for winter maintenance personnel and traveler information systems within MDT as well as sharing the data outside MDT to 511-provider Iteris, NOAA, and MSU/WTI for multistate traveler info/operations systems. The core sensor setup that exists at virtually all 73 ESS includes an air temperature and humidity sensor, wind speed and direction sensor, in-pavement sensor, subsurface temperature sensor, precipitation occurrence sensor, and a camera; select sites (6 or fewer) also have advanced precipitation sensors, visibility sensors, or infrared illuminators for nighttime camera images. MDT’s internal RWIS software for data polling, processing and display is a legacy Vaisala system (SCAN Web 6.0) that no longer has the ability to provide weather condition or sensor/site status alarms, limited usability on mobile devices, and no forecasting functionality. Alternative sensors including various atmospheric combination sensors, infrared lights for cameras, visibility sensors, advanced precipitation sensors, and non-invasive sensors are available and may provide additional functionality or configuration options compared to the current core sensor setup. Many alternative RWIS software systems exist categorized by their functionality from basic observational only software to options for alerting, forecasting, mobile sensor integration and automated performance metric functionalities. An extensive benefit-cost analysis was conducted to investigate outcomes related to using different software functionalities and geographic expansion alternatives. Agency specific benefits exceed costs for all three alternative software systems (alerting, forecasting and automated performance metrics) when considering the current ESS sites. The highest agency specific benefit-cost ratios were found to be possible with forecasting and automated performance metric functionalities. Total benefits, including societal benefits, exceed costs for all ESS expansion options (base, simple, non-invasive, and mobile) and all alternative software systems (alerting, forecasting and automated performance metrics). The highest total benefit-cost ratios were found to be possible with forecasting and automated performance metric functionalities. Most scenarios with the highest total benefit-cost ratios are also the most costly and may or may not be feasible with current MDT funding availability. Some of the most promising scenarios may require significant investments of hundreds of thousands of dollars above current RWIS funding amounts. One scenario, obtaining alerting functionality without expanding sites, is potentially both relatively low cost and highly beneficial, depending on the specific software product used. An ESS site prioritization model was developed to increase the objectivity of a traditionally subjective practice for determining the best ESS placement given multiple potential sites. The model quantifies the overall merit of potential ESS sites based on historical weather conditions, traffic amounts, crash history, existing geographic coverage and opportunistic factors related to the availability of power and communications. The model is customizable and allows MDT to place selected weights on certain aspects according to their agency priorities. Overall the MDT RWIS program provides many benefits to MDT users and ultimately the traveling public. A number of minor practical recommendations and larger program future direction possibilities exist, stemming from the tasks considered as a whole. MDT should consider requiring new RWIS sensor, hardware, and software options be as flexible as possible through the use of non-proprietary communications and compatibilities, allowing for easy integration of different equipment that may be superior or more economical regardless of the provider. RWIS data and camera images should be updated every 15 minutes or less for all sites as some RWIS data users and literature suggest that 15 minutes can make a considerable difference in terms of winter maintenance treatments, especially at the start of a storm. Aviation users would benefit by including a horizon view at all ESS with PTZ cameras, especially considering adding this view at ESS with PTZ cameras will not detract from primary road monitoring images. Some winter maintenance personnel in remote areas currently have little or no RWIS coverage so it may be beneficial to make those personnel aware of resources like http://mesowest.utah.edu/ that have additional weather observations from non-RWIS sites around the state. MDT could benefit from a less subjective site selection process that is data driven by utilizing the ESS prioritization model with agency selected weights that reflect their knowledge and preferences to plan future RWIS installations. Lastly a number of future directions show promise in reducing agency costs and increasing safety and mobility for travelers. These future directions require obtaining new software products and services and considering different geographic expansions all at varying initial and ongoing levels of investment and some with non-trivial changes to winter maintenance practices. (Author/publisher)
Samenvatting