[1] There have been a number of notable changes in this important east–west route which follows the north Sussex border with Kent and Surrey.

Both routes are winding and narrow and both have bridges with single file traffic.

The section from the west of Felbridge as far as Three Bridges has been improved and partially rerouted.

In the late 1980s, it was rerouted along the newly constructed Copthorne Link Road to Junction 10 of the M23, and in the early 1990s was multiplexed south along the M23 to Junction 11 at Pease Pottage, and along the then newly constructed SW Crawley Bypass.

The section west of Crawley was upgraded to dual carriageway, and the route now follows Horsham's Northern Bypass (opened 1989; traffic previously went through the town) to its junction with the A24, then multiplexes south with the A24 (West Bypass), now also dual carriageway, to Broadbridge Heath where instead of going through the village it follows its bypass together with the A281.