It sure is. I have noticed that generally, unless otherwise noted, everything on a city track is legal as long as you don't touch the walls. Since nothing was noted you're fine if you get up on that curb without hitting the armco. It is possible under the tunnel and up the hill before the hairpin as I found last night.

I'm note sure it is any faster though.
Careful in sector three as the curbs (the actual curbs, not the red and whites) there in the middle esses coincide with invisible walls if I remember correctly.
The only city track I can think of that has extra restrictions is Rome with the large run off in the last turns.