In the west, its route starts in the town of Shenfield at the junction of the A1023(51°37′50″N0°19′16″E / 51.6305°N 0.3212°E / 51.6305; 0.3212 (A129 road (western end))), where it is called Hutton Road. From the town the road soon becomes Rayleigh Road and it runs through the adjacent town of Hutton and through a rural area until it enters the boundary of Billericay and becomes London Road. In the centre of Billericay the A129 is named Sun Street,at this point the road is one way and is only accessed from the Crays Hill direction. Drivers wishing to continue on this road have to turn right on the roundabout at Sun corner onto the B1007 Laindon Road, then turn left at the roundabout onto the A176 which rejoins the A129 which then becomes Southend Road. To the south of Billericay the road enters the village of Crays Hill and becomes Crays Hill. On exiting the village it is again London Road.