My reading is that it protects the agency from the charge of trespass. The INTENT being to enable the agents of Metrorail to gain access to their facilities without the neeed for:
1) prior approval of the property owner for lands next to the Metro rail property
and
2) without the need for a warrant to enter and cross such lands
while the INTENT may be reasonable, the wording and execution of this law leaves a lot to be desired. Lots of other ways this could have been addressed.
Sounds pretty much like any municipal utility. They have a right to enter your property for reading meters or repairing their lines/equipment once they've determined the need, and given notice.
As I see it...
1) This is limited to premises adjacent to the Washington Metropolitan Area Transit Authority system
2) Courts will have to confine this law to within constitutional limits of probable cause and precedent that requires a warrant for house searches except for exigent circumstances or consent.