Approx. 99 miles, 2 hours, 10 minutes.
The ground is well signposted from the A11 and A47. From the southern bypass (A47) take the A146 into the city. At the traffic lights turn right and follow the outer ring road: Left at the roundabout. Right at the next lights. Follow the inner ring road round to the right, over the river and the ground is on your right. If in doubt follow signs for the the railway station until you get to the river (where the rail station is off to the left and ground on your right). 
The best car park for away fans is Norfolk County Hall, which is well sign posted on the left of the A146, as you follow signs towards the ground from the Southern Bypass. It is was Free!
Rail station; top middle, the blue blob. Coach station; bottom left, Surrey Street. Stadium; botton right, Carrow Road.
(Thanks to www.footballgroundguide for stadium directions.)