In previous years the route would leave Place De L'Eperon and continue Rue De La Galere then right on to Quai Louis Blanc before turning right again in to the road (which has no name according to Google) and in turn the tunnel until it reached Avenue de Paderborn and the place in front of the Cathedral.
The new route will possibly be a bit shorter and given the lack of hill through the tunnel it will prevent some, but I bet not all, of the supercars from burning out their clutches on the slow climb.