Mmm - thinking further about this, there is a precedent - this highway bridge in Prague actually has the Metro running in a tube underneath it - https://www.google.com/maps/@50.0650592,14.4285975,3a,51.1y,87.9h,96.91t/data=!3m6!1e1!3m4!1s8WDelnI3bpaj29L7Pyq-8A!2e0!7i16384!8i8192 - like a 'tunnel in the sky' - it does stop passengers being blinded by the sudden light, before they are plunged back under the ground at the far side of the valley.