|Distance:||6.2 miles (10 km)|
|Meets:||M11, A10, A1301, A1134, A14, A10|
|Route outline (key)|
The A1309 follows the former route of the A10 through Cambridge, although it is only well-defined at its ends due to the dominance of other roads it multiplexes with inside the city's ring road. Through traffic on the A10 is now signed to use the M11 and A14 instead.
The A10 is left behind at M11 J11 and heads northwards into town. A dualled section leads to traffic lights where a spur of the A1301 heads off to the right and a slip road peels off to the left to access the Park and Ride. Full access is provided at the next set of traffic lights. The road then goes over the Cambridgeshire Guided Busway (used by park and ride buses), then adjacent sets of traffic lights provide access to Waitrose and the mainline of the A1301.
The road continues north along Trumpington High Street. As the road leaves the village and becomes more rural again a set of traffic lights is reached on the A1134 Cambridge Ring Road, which is some distance from the city centre on this side. The southern section of the A1309 ends here as roads inside the ring road take precedence. Through traffic on the A1309 would continue ahead along the A1134.
The former A10 continues into the city centre along the present A1134 Trumpington Road. When that road bears left along The Fen Causeway, the quickest way back to the A1309 is to turn right along the A603, which skirts the eastern side of the city centre to rejoin the A1134 just to the south of the River Cam. Following the A1134 across the river leads to a roundabout in the suburb of Chesterton, where the A1309 finally reappears after over 3 miles in a multiplex.
The A1309 continues northeastwards along Milton Road through the suburbs. On the edge of town the Guided Busway turns left at traffic lights at what used to be a level crossing, then the Cambridge Science Park is passed. A short dualled section leads to A14 J33, where the A1309 ends and the A10 reappears.