Evaluation of the positional accuracy of subsurface utilities

Since WWII, the urban underworlds have become a web of utility lines, including telecommunication lines, buried electricity lines, gas mains, watermains, cable TV, fiber optic cables, street lighting, and storm and sanitary sewers. From preliminary design stages to breaking ground on new construction projects; owners, designers, engineers, and contractors rely on existing underground utility records as an initial source of information. There is a constant need for underground utility information and most of the city's existing utility records are not only irretrievable, but are also out-of-date. According to research done in the past, records and visible feature surveys by site are a significant percentage off the mark and, in some cases, considerably worse. This study focuses on the evaluation of the positional accuracy of subsurface utilities within seven projects, within the City of Toronto, using an offset approach. It also aims to reveal the magnitude of the problem surrounding the obtainment, analyzation, and interpretation of information with respect to underground infrastructure facilities. None of the projects show any relationship or correlation with positional accuracy and the factors that are thought to affect the accuracy of underground utility information (e.g. type of soil, type of utility, date of installation, right-of-way, etc.). The analysis indicates a clear indication of no systematic patterns between the right-of-way parameters and utility type parameters. Based on the results of this study it can be stated that the process of obtaining subsurface utility information is still a time-consuming, inefficient, costly, and difficult process.