I assume that the mesh is totally different : the jacket is a high poly with subsurf while the road is a low poly flat mesh. It is like applying smooth on a cube : you get black artifacts on all edges.
I said that they are not intended to be used at the same time.
I didn't meant that it is not possible to use bump and Disp at the same time : it is just not always convenient.
French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.