|To:||Spittleborough Roundabout (SU102828)|
|Length:||7 miles (11.3 km)|
|Meets:||A346, A4361, M4, A3102|
|Route outline (key)|
It starts on the A346 on the eastern edge of Chiseldon and heads westwards around the village, with a mini-roundabout at one point.
The road passes south of Hodson before reaching a T-junction near Burderop, where it turns to the right. It then descends Brimble Hill before entering Wroughton, where it reaches a mini-roundabout on the A4361 (former A361).
For many years this was the end of the B4005. However, following completion of the M4, the B4005 was extended west via a short multiplex along the A4361 before leaving Wroughton northwestward. After coming within yards of the motorway our road turns westwards to run parallel as far as junction 16, where it also meets the A3102.