The B2031 is a short B-road just inside the southern section of the M25.
It starts at a mini roundabout on the B2030 on the western edge of Caterham and heads west, passing through Chaldon. To the left is Six Brothers Field, one of the National Trust's smallest holdings (and named after the donor and his five brothers). The road then crosses Alderstead Heath where it bends sharply southwards.
Eventually it passes over the M23 just to the south of junction 7 to terminate immediately afterwards at a 'give way' junction on the A23 at Merstham.
An amended OpenStreetMap trace for this route awaits uploading to the SABRE Wiki.