Extreme Vehicle Loads on Bridges: Evaluating and Regulating Farm Equipment in Wisconsin

Abstract

In May 2014, the Wisconsin legislature passed Act 377. Among other things, the act creates an increased weight allowance for vehicles classified as implements of husbandry (IoH), known to most simply as farm vehicles. These vehicles, which are both large and heavy, were designed for use in the field, but in today’s modern infrastructure, they must sometimes navigate roads and bridges as well. The increased weight allowance is a modification of the federal bridge formula (FBF). It allows IoH to operate at 15% above FBF limitations for both axle and gross weights. The act includes partial exemptions for certain implements and creates a permitting structure for implements that exceed the stated limits. The act attempts to strike a balance between the needs of the farming community in Wisconsin and the effects of heavy vehicles on the inventory bridges in the state. In this paper, the work done by the Wisconsin Department of Transportation’s Bureau of Structures to render a structural recommendation concerning operation of IoH on the Wisconsin bridge inventory is documented. Both analysis work to assess risk to the inventory as a whole and permitting processes and procedures to address IoH on a more local level are included. The intent is that other state departments of transportation and infrastructure owners benefit from Wisconsin’s experiences.