Transportation planners are increasingly recognizing the importance of access in enabling employment growth and better paying job opportunities for residents. Although regional economic impact analysis is often an important element of transportation investment evaluation by state departments of transportation, it can be particularly challenging for metropolitan area planners because existing economic modeling methods do not fully account for the multifaceted roles that transportation links play in affecting access within large, polycentric metropolitan areas. This article examines these issues and presents information from a study of the Chicago region, to evaluate statistical relationships of employment cluster size and wage levels to zonal differences in business-to-business connectivity and population connectivity. It presents elasticities of employment and wage impact associated with various access measures for different sectors of the economy. These findings point to the importance of transportation planners considering the impacts on connectivity to both population markets and employment centers when evaluating the potential economic implications of proposed transportation system improvements in large, polycentric metropolitan areas. The article then lays out directions for future research and practice to improve transportation project evaluation and planning.

Although a significant body of research has focused on employment agglomeration at an urban level, this paper presents a broader view that also includes new empirical research on wider regional and intermodal access and its economic implications. The analysis shows how business clustering (employment agglomeration) can occur at different scales and in different forms, reflecting a range of needs to access local and regional populations, suppliers, and customers, as well as intermodal gateways that provide access to national and global markets. These different types of access have broader economic development and productivity implications that are particularly important for transportation planners who evaluate proposals for freight and passenger modal investments connecting communities and intermodal facilities. To address these issues, the paper brings together three complementary perspectives: (a) transportation planning literature that distinguishes types of transportation investment and plans; (b) site location literature that defines business location decision processes and their spatial scale; and (c) economic research that provides a basis for defining scale economies and productivity effects. It presents results of a new U.S. study that develops statistical relationships between types of access and industries in relation to their relative concentration and productivity at a county level. The results show the importance for transportation planners to consider freight access as well as customer and worker access. They also indicate the potential for decision bias if project prioritization and cost–benefit analyses fail to consider the full range of spatial scales relevant for assessing market access. The article discusses implications of these findings in terms practical applications for transportation investment planning, and it highlights remaining needs for further research.