Developing a Chained Fisher Construction Cost Index for Structural Steel Girder Bridges

Abstract

The construction cost index is widely used by state departments of transportation (DOTs) for budgeting purposes, and to arrive at engineers’ estimates on projects for bid. State DOTs typically develop cost indexes at the construction program level. There is little information available on developing cost indexes for bridge types. This paper outlines how such a bridge-level cost index can be developed. The bridge-level cost index was developed from 19 weighted bid items aggregated into four weighted components (groups) of bid items, and then aggregated to the weighted bridge system. Using publicly available data from Ohio DOT, on historical bid items, chained Fisher indexes were developed for typical Ohio DOT structural steel girder bridges. In addition, forecasting beyond 2021 was computed using a well-fitted regression model. The findings from this research could help Ohio DOT to accurately estimate the cost to construct structural steel girder bridges based on price changes and price trends. In addition, the result of this research allows for long-term planning and budgeting of costs for similar bridge types within the state of Ohio. In their simplest form, the cost indexes generated from this research will help paint a picture of changes in the cost of construction from one specific year to another at a granular level. This research contributes to the body of knowledge by offering detailed steps on how to develop construction cost indexes at a granular level and specifically for structural steel girder bridges.