Enhancement of bridge live loads using weigh-in-motion data

Abstract

Over the past century, the American Association of State Highway and Transportation Officials (AASHTO)-specified live loads have been evolving to catch up with the ever-changing knowledge and trends of vehicular traffic. The latest loads are based on past Canadian traffic data, and may not represent modern or future traffic conditions in some US jurisdictions. Today, weigh-in-motion (WIM) systems can provide a solution to this dilemma by providing valuable site-specific traffic data for bridge design and evaluation, weight-limit enforcement, and the likelihood of illegally overloaded trucks causing premature bridge deterioration. Bridge owners have long recognized the importance of incorporating site- or state-specific truck loads in their bridge evaluation and preservation programs. The AASHTO LRFD and LRFR Bridge Specifications have evolved to advance the trend toward information-sensitive specification formulation. When warranted, the specified live loads can be enhanced utilizing more relevant site or route data. This paper reviews the evolution of US bridge design live loads, and discusses the possible enhancement of bridge live loads and load factors using WIM data. The paper presents recent investigations for evaluating the design live loads for the State of New York, and calibrating the live load factors used in rating for the State of Oregon using WIM data. The New York investigation indicates that truck loads at two studied sites may be significantly heavier than the AASHTO-specified loads. It also indicates that WIM enhanced site-specific fatigue design loading is significantly heavier than the AASHTO LRFD fatigue design truck. In the Oregon investigation, state-specific WIM data resulted in a significant reduction in the live load factor for legal and permit trucks for the entire State of Oregon, which is attributable to the State’s regulatory and enforcement environment.