Just a simple question. Can you use a double train portal for an automobile and truck portal or does it need to be modified to look real?
Sure. The ones representing cut stone would be appropriate for an older two lane highway while a pair of concrete ones would be better for a modern four lane highway. Don't forget matching wing walls as appropriate.
Suggestion - Google images of "highway tunnels" and see what turns up. There are many variations, including no portals at all.
Thanks, Jim
JIm, would they be as high as the RR type?
I think you're asking a huge question. I would imagine that the size and shape of an auto tunnel would depend on many things. I'm sure that Uncle Sam has federal standards.
Your best bet is to do some resarch but I don't see why the tunnels designed for railway use couldn't be used as is. It's your railroad and your layout!
I know the Pennsylvania Turnpike's route is that of the planned South Pennsylvania. Were some of the railroad tunnels already bored before the work stopped on the railroad? I know the portals are rather high.
Gene
The "Westrock" tunnel is a great example of a double bore;it is functional, very good workmanship, and just plain old good looks. This is at the Hamden/New Haven town line at West Rock on the Wilbur Cross Parkway.
Rich