An exploration of issues related to the study of generated traffic and other impacts arising from highway improvements

Generated traffic has received considerable worldwide attention for its ability to congest newly built roads or return improved roads to their original congested states. By investigating impacts resulting from two contentious highway projects in the Hamilton Census Metropolitan Area, Canada, we address two outstanding issues relating to the study of generated traffic. First, we find that the type of measure used to quantify the phenomenon can impact significantly evidence of its existence. Second, we decompose successfully generated traffic into its constituent parts, namely, induced travel and diverted travel. We also identify the source of each component. Next, we document statistically significant changes in the spatial distribution of traffic flows in the vicinities of the new expressways and throughout the entire network. Finally, our analysis of traffic congestion and vehicular emissions of three pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) suggests that while the new expressways may prove beneficial to the system as a whole, this is not the case for their immediate environs.