Many urban rail transit systems share a common transportation corridor or right-of-way with FRA-compliant freight or passenger trains. Existing federal railroad safety statutes do not specify requirements for this sort of application. As the mileage of shared-use corridors increases, there is increasing concern among federal and state regulators, railroads, and transit agencies about the potential for accidents that could stem from FRA-compliant and noncompliant rolling stock operating near each other in a shared-use corridor. This paper describes the extent and characteristics of shared-use corridors in the United States, derived from a recent survey undertaken on behalf of the FRA. The paper provides an overview of current practice in the design and operation of shared-use corridors and suggests a need for research leading to standardizations of practice to address potential safety and regulatory concerns.