The A306 links the A3 at Putney Heath to the A4 at Hammersmith. For a road ending less than 7 km from Piccadilly Circus, it is surprisingly rural for much of its length.
The route starts on Putney Heath, by Wimbledon Common, at the last set of traffic lights on the A3 leaving London – which is the second set entering London because of those at the Robin Hood junction.
The closure of the Robin Hood Gate entrance to Richmond Park has diverted a lot of traffic onto Roehampton Lane, making it much busier than before. It sweeps down the hill to Roehampton, to reach the junction with the South Circular Road at Barnes Common. This junction was for long known as the Red Rover after the pub on the corner, and while the pub has now changed its name, the title is still used on road signs on its approaches. Across Barnes Common now, along Rocks Lane, past Barnes railway station in its rural setting, and on to Barn Elms.
From here to Hammersmith the road is known as Castelnau - a common name in the south of France (it means "New Castle" in the medieval "Langue d'Oc") but unusual in west London. This has probably the longest bus lane in London (although the former one on the M4 was definitely longer), which helps to control the flow at the pinch point ahead: Hammersmith Bridge. The first Hammersmith Bridge was built in the 1820s and was the first suspension bridge in London. It was replaced by the present bridge in 1887. It has been subjected to terrorist attacks no less than three times, in 1939, 1996 and 2000, although the most extensive damage was done in 1984 when something in excess of the weight limit managed to dislodge the chains from their bearings on the towers. Now a width limit is also imposed. No large vehicles are allowed, but small buses may cross, one at a time.
Hammersmith Bridge was closed to motor traffic in April 2019 after cracks were discovered in the bridge's pedestals. The following year, it was closed to all traffic completely.
After the bridge, the A306 passed under the Hammersmith Flyover, to end on the Hammersmith gyratory. As this part is now completely detached from the section the other side of the Thames, its present and future status is uncertain.
