The road starts at a west-facing GSJ on the A428 (former A45) to the south of Madingley. The A1303 now heads east into the centre of Cambridge whilst the A428 turns northerly to bypass the city. After passing the American Cemetery we reach the M11 which has south-facing sliproads at J13. We then continue east past the park & ride and several of the science buildings belonging to Cambridge University. Any buildings alongside the road are set back and not really visible.
At one of many sets of traffic lights the A1134 ring road comes in from the left and multiplexes with us for a short distance to a mini-roundabout. It is not clear which road is dominant. That road then bears right and we bear left, with the road now actually lined with buildings. For some reason we are now inside the ring road. At traffic lights by the Cambridge & County Folk Museum we meet what used to be a major crossroads in the city. To the left is the former A604 whilst to the right and ahead were the A10; the A45 multiplexed along that to the right over the River Cam.
Now on the former A10, we head northeastwards along Chesterton Road, with the River Cam to our right. We soon reach the Mitcham's Corner gyratory where we cannon off the A1134 ring road (which has taken a much more complicated route to get here) and leave the former A10. That road is met again at the next roundabout (again it has taken a longer route) and now finally we become the junior partner in a multiplex along the ring road. It heads south across the river to meet the A603 then joins the former A45 heading east. At a roundabout near the airport it turns right to continue clockwise around the city and the A1303 regains its number by continuing ahead.
Cambridge - Newmarket
We run along a straight road between the park & ride and the airport runway before the Cambridge northern bypass, now numbered A14, is met once again at J35. We cross this heading due north before turning eastwards once again to pass to the south of Stow-cum-Quy. We continue parallel to the A14 across the fields and skirt Bottisham before reaching the Newmarket bypass. We pass over the A14 and the A11, which join just to the north at J36. For good measure the westbound A14 is joined by a slip road from the A1303 - but no other movements to or from this road are possible.
We continue northeastwards along a dead-straight road across Newmarket Heath, with facilities devoted to horses on both sides. The road remains pleasantly wooded until a roundabout is reached on the A1304 (former A11), where the road ends and the National Stud is also accessible.