The importance of increments to an existing highway system depends upon their contributions to the accessibility provided by the existing network. Nearly 40 years ago, Mohring [1965] suggested this logic for planning optimal highway investment programs. He argued it could be implemented by...

This paper outlines a new framework for gauging the properties of quasi-experimental estimates of the willingness to pay (WTP) for changes in environmental and other non-market amenities. As a rule, quasi-experimental methods cannot offer alternative hypotheses to judge the quality of their...