The San Joaquin kit fox is a federal endangered and state threatened species occurring in 16 California counties. More than 340 miles of two-lane highway that run through San Joaquin kit fox habitat are scheduled for widening projects this year, and there are concerns that the projects will reduce fox habitat connectivity by restricting the animals’ movements. Presently, research is needed to measure the impact of four-lane highways on kit fox movements. With limited opportunities to study San Joaquin kit fox populations directly, WTI will conduct field studies on two phenotypically and ecologically similar fox species, the desert kit fox and swift fox. Study objectives will be to determine whether 4-lane highways inhibit desert kit and swift fox movements and to measure how and where foxes cross 4-lane highways, with a particular focus on below-grade passage structures. Collected data will be used to make inferences for San Joaquin kit foxes, and to develop guidelines for highway-expansion projects with effective below-grade kit fox crossings.