The B3420 is a medium-length B-road in central Hampshire.
The road starts on the A3057 to the east of Goodworth Clatford and only a short distance south of the Andover bypass. It follows Winchester Road from the outset, showing where we'll end up. Initially we follow a fairly straight route across the fields but soon the road begins to descend into the valley of the River Test, which needs a couple of hairpins and some sharp bends in the village of Wherwell.
After going through the narrow streets of the village there's a sharp right-hand bend to cross the river, with the B3048 continuing at 12 o' clock. There are actually a few river channels here and there's another sharp bend, left this time, after the final crossing. The climb out of the valley is considerably less steep than the descent. It's not long before we reach the historic Roman road north of Winchester and then the A30.
The B3420 approaching the modern A34 and A272 near Worthy Down
It would appear that the B3420 ends here as the road on the far side of the staggered crossroads is the A272. However, if we follow that for over 3 dead-straight miles onto Worthy Down we reach a roundabout, part of a GSJ with the A34, where the A272 disappears and the B3420 takes on the road ahead. The road remains straight as it enters the suburbs of Winchester along Andover Road and there's even a (heavily butchered) dual section for a short while.
After meeting the B3041 we go over the railway line and descend into the city centre. At a crossroads signs advise our road is for Southampton whilst all other traffic is directed left onto the B3330. We then continue along Sussex Street although northbound traffic leaves us one block further south and follows a longer course via the station. The two directions meet again by the Plague Monument and the B3420 ends just afterwards at a mini-roundabout on the B3040.
The B3420 was one of the first road numbers which was not allocated in sequence, appearing on 1st April, 1933, when the former A342 was downgraded to a B road, up to the A34 on Worthy Down.
In 1969, when the A34 King's Worthy Link opened, it took over the old A34 route as far as the southern end of Andover Road, ending on what was the A3091.
In 1995, the opening of the M3 over Twyford Down caused all A roads in Winchester to be downgraded, and the A272 was routed over part of the old B3420 mainline from the A34 to the A30. In Winchester, the road was slightly extended down Sussex Street over the former A3091.