The B172 is a short B-road in the vicinity of Epping Forest.
It starts on the A113 at Abridge and heads north over the River Roding and across fields to go under the M11, before turning to head west. It then crosses the Central Line, originally at a level crossing adjacent to Theydon Bois station but now uses a bridge just to the south. Theydon Bois itself lies on the far side of the tracks and the road goes through the village before entering Epping Forest. It ends at the Wake Arms Roundabout at Jack's Hill on the original line of the A11.