The A3216 is a surprisingly long A-road in west central London.
The route starts at traffic lights on the A4 by Knightsbridge tube station and heads south along the dead-straight Sloane Street. Apart from a couple of blocks skirting Cadogan Place Gardens, the road is built-up for its entire length. The road soon reaches Sloane Square, its original southern end, where it crosses the A3217. Although the Square is essentially a roundabout we seem to join it at a T-junction rather than a merge.
We leave Sloane Square at traffic lights directly opposite where we entered and continue south along Lower Sloane Street, which was the original western end of the A3214. We finally leave the dead-straight alignment we've been following since Knightsbridge by bending to the left, after which the A3214 turns left at traffic lights. Now on the original line of the B302, we run southeastwards along Chelsea Bridge Road, with the former Chelsea Barracks (now demolished) on the left and Chelsea Royal Hospital on the right; its grounds merge into Ranelagh Gardens before we cross the A3212 at traffic lights to cross Chelsea Bridge over the River Thames.
On the Surrey bank of the river we skirt the eastern edge of Battersea Park to reach the Queen's Circus roundabout, which gives access only to unclassified roads. A short distance further on we cross the A3205 at traffic lights and go under the railway line from Victoria to Clapham Junction immediately afterwards. We zigzag under a couple more railway lines, one by Queenstown Road station on the Waterloo line, before our route straightens out once more.
The road heads south along the largely residential Queenstown Road. It bends to the left to cross the A3036 at traffic lights and then continues along the leafy Cedars Road to end at traffic lights on the A3 on the northern edge of Clapham Common.
An amended OpenStreetMap trace for this route awaits uploading to the SABRE Wiki.