What was done on the Train level for Uncharted 2 where it constantly goes up and down, left and right was there was 1 main prototype train track created (in your case a road section). And then a ton of variants made of that piece to account for all the possible variations like left turn up 15 degrees, left turn down 35…
Use Loft. Watch this if you don't know those yet: http://cg.tutsplus.com/tutorials/autodesk-3ds-max/using-splines-to-quickly-create-highly-complex-geometry-in-3ds-max/
I'm building a driving game course at the moment. I decided against modular for the reasons you state, it doesn't feel organic and natural, especially for a windy mountain course which is what I'm building. It would probably be more suitable for a city course. What I'm doing now is simply using line and sweep, it's easy…