This article is about the original B3123 in Bristol.
For the current B3123 near Exeter, see B3123
.For the reserved route in Wells, see B3123 (Wells)
(former B3123) Jacob's Wells Road
The B3123 originally ran to the west of Brandon Hill Park in Bristol, forming a curved link between what was then the B3122 and the A4018.
By 1926, the B3122 here had been upgraded to become part of the A36 (later A4) with the opening of the Portway. The existence of the route, being entirely north of the Avon, yet receiving a 3 zone number, gives evidence that the A4018 formed part of the original 3 / 4 zone boundary.
Today, the road is in the 4 zone, being north of the A4, and is numbered B4466. This change presumably happened in 1935 when the A4 was extended west along the former A36 route.