Starting from the assumption that the U.S. is not prepared for an immediate transition to dedicated track systems for true high-speed rail, examines the interim use of shared rail corridors, addressing the problem of configuring tracks for both rapid, light-axle passenger service and slower, heavy-axle freight hauling on the same roadbeds. Present train equipment requires “incremental” modifications of track, including straightening curves, reducing grades, and laying new ties, in some cases made of concrete. Examines other advances involved in mixed use of corridors, including more sophisticated signaling systems and more crash-safe rail cars. Focuses on ways to minimize the risk that share