Determining When to Place and Remove Spring Load Restrictions on Low-Volume Roads

Damage to low-volume roads in seasonal frost areas can be kept to a minimum by implementing seasonal load restrictions (SLRs). However, not all agencies responsible for road management implement such restrictions, and among those that do, there is no standard technique. Some use qualitative methods, such as observation or dates. Others use quantitative methods, such as measuring or estimating stiffness or subsurface temperature. Loss and recovery of summertime pavement strengths can be directly measured with a falling-weight deflectometer (FWD). Alternatively, mathematical models of varying levels of complexity, using meteorological data, are in existence or are undergoing development for SLR placement. However, initial investment for an FWD can be prohibitive for agencies such as the U.S. Department of Agriculture Forest Service (FS), for which road management is not a primary mission. Similarly, such agencies have limited personnel to conduct detailed calculations required of complex mathematical models. Consequently, easy-to-use, low-cost alternatives are needed. In cooperation with other partnering agencies, FS has recently been evaluating several techniques for determining when to place and remove SLRs. Three methods that appear promising include (a) subsurface instrumentation for temperature and moisture, (b) portable or lightweight FWDs, and (c) the thaw index. Technology-and-development efforts in each of these areas are outlined here; field test programs, observations, and analysis procedures are discussed; and recommendations for implementing each method are provided.