Tunnel Considerations Tunnels are not just holes in the ground, each tunnel is different and each requires a different approach to how it is built, what lighting and ventilation is needed, how much drainage and falling rock support is needed, etc. The route of the BorderTransportationSystem does bump into mountains and large hills that may require cuts through the terrain or tunnels through the terrain.  The route tries to avoid as many of these situations as it can, but the fact remains that there will be tunnels along the route. Index of ... Lighting Maintenance areas and access to Monitoring sensors Mountain top Fencing Pressure prevention Rock securement Separate tunnels Ventilation systems Water removal Where are the tunnels needed