The purpose of this paper is to discuss the use of subgrade temperature data, measured by permanently installed temperature sensors called thermistors, to administer spring road restrictions on asphalt surface roads within the kootenai national forest (northwestern montana). The restrictions normally apply to logging trucks (three axles plus two axle trailers--approximately 80, 000 lb gross). The interpretation of the data from the thermistor installations has providedan acceptable, rational approach to timing the spring restrictions.At present there are about 70 thermistor strings scattered over 300miles of roads. Data are collected on the thermistor strings starting in december on a weekly basis, a schedule that is stepped up to daily readings as thaw conditions approach. The readings from just below the asphalt mat and the average reading for the whole string areanalyzed with weather forecasts for use in predicting the need for load restrictions. The actual restrictions are placed when the thermistors located just below the mat on one or more strings indicate a thawed or nearly thawed condition. The success of the program can beattributed to the effort put into an information and education program aimed at the principal users and forest managers. Problems with installations have been minor. Each thermistor string installation ranges in cost between $250 and $450; however, during the past 3 yr, surface maintenance repair costs have been reduced significantly (upto 50% annually on some roads). This paper appears in transportation research record no. 1252, Design, management, and operation of pavements.
Abstract