The road used to terminate at the seaside town of Bridlington, until the opening of the Driffield by-pass caused the final section to be renumbered as the A614.

[3] There are a number of scheduled monuments that lay alongside the A166, most notably in the area of Garrowby Hill: In 1983, the Driffield by-pass was built and became the route of the A166, which had previously gone through the centre of the busy market town.

In 2008, a feasibility study was carried out and proposals were put forward on behalf of the East Riding of Yorkshire Council for an alternative crossing of the River Derwent at Stamford Bridge.

Alternative routes included utilising the disused York to Beverley railway line crossing downstream from the current bridge.

The report concluded that the best options did not score well enough for the Regional Transport Board to take forward and should not be pursued.

From here the road gradually turns in an easterly direction until it is required to cross the River Derwent at Stamford Bridge.

There are several places where the road has been widened to allow slower traffic ascending or descending to pull to the left and allow faster vehicles to pass.

Travelling in an easterly direction, the road follows an ancient green lane until it reaches the village of Wetwang.