Over / Underpasses The BorderTransportationSystem will be crossing roads, rivers, valleys, canals, railroads, and highways as it makes it way from San Diego to Brownsville.  Each of these crossings has to allow the system to cross without interruption, allow the various items to pass over or under the system, and at the same time provide border security to both nations.  Thus, several individual and unique proposals are being introduced with the Pro's and Con's of each.  Index of ... Animal crossings ... Buried Crossings ... Crossings may not block railroads Highway crossings Service road crossings River and canal crossings ...