Conclusion: Measuring What Matters

Whether as performance metric, planning tool, or in benefit-cost analysis, accessibility can quantify how state and local departments of transportation directly and indirectly change land use. Indirect land use change can be anticipated by mapping places where accessibility will change given a new network investment, as business and residential investment will follow such improvement. As this development plays out, with people following new access, trips taken from these origins increase, until over the long run there is congestion at peak demand. 

In the short term, accessibility change from year to year depends on the network type. Small improvements in the network speeding travel to connected destinations can improve access for transit trips. But year over year changes in auto access are much more driven by the regional economy than by changes in transportation. Importantly, the access to opportunities for residents can go up even as congestion goes up! Adding reachable jobs is clearly beneficial even if congestion increases at the same time, and accessibility is one way to communicate the benefits (reachable destinations) instead of the side effects (slightly slower travel). 

Finally, the greatest impact of using accessibility as a measurement is in how it induces planners and engineers to consider the land use and transportation systems together. While challenges in coordination and differing areas of responsibility require additional effort on all sides, an outcome based in accessibility means the agencies are measuring how well people can reach the destinations that support their daily lives, and that should be what truly matters.