WOAH..how did you do that without photoshop? it appears as if the bus was stopped because the wheels weren't spinning. that, or you used a high shutter speed to stop motion, and then motion blurred the edges of the bus. Do share your secret please!
You applied motion blur only to the front and rear of the bus, or to the road as well?
My guess is that you panned to 'freeze' the bus and create actual motion blur for the rest of the elements. Then you applied selective motion blur to the bus, taking care to exclude the center of the bus, and also the D700 picture and bus route number...
am I right?