Beware of the Park Avenue Viaduct southbound (downtown) on weekdays. Back before August 2008 this elevated ramp alongside Grand Central Terminal and its corresponding Murray Hill tunnel bypassed the busy crosstown thoroughfares of 34th and 42nd. That is still the case, but only for northbound traffic. Downtown-bound traffic has in fact worsened to the point it makes no sense to be on the viaduct. Take Lexington or 5th around instead. What put a halt to two-way traffic in the tunnel back in 2008 was the need to protect pedestrian safety on 33rd Street.