Hahaha I get it now, thank you. Nonetheless, I still stand by my comment.

Oh snap I thought surfing was when you transfer from one car to another. This sport sounds kind-of knarly but you could lose you head doing it in a tunnel standing atop a car.

So basically it would be safer to do it on a non-L train since it wouldn't be subject to weather conditions and wind? Harder to slip on the A train I'd bet.