|Distance:||1.6 miles (2.6 km)|
|Meets:||A726, A898, M898, A8|
|Route outline (key)|
It starts at the Toll Plaza Interchange, Junction 1, and indeed the terminal junction, of the M898, which becomes the A898 overhead. The eastern continuation of the B815 is the A726, heading east through Erskine.
Heading west, the B815 passes the grounds of Erskine Hospital, and then reaches a roundabout at the entrance to the Hewlett Packard Factory. For the next mile, the road gently curves and undulates past a number of junctions with minor roads and lanes before crossing the M8 and entering Bishopton. The Old Greenock Road (never the A8) is crossed almost immediately before the traffic-light controlled crossroads with the A8.
The 1922 Road Lists state that the B815 ran from Bishopton to Old Kilpatrick, which is on the other side of the Clyde! However, while the road in Bishopton is still called Ferry Road, the 1923 map shows that the Ferry itself was part of the A740 (Paisley - Old Kilpatrick) (later renumbered A726), with the B815 meeting it a little to the east of the modern Toll Plaza Interchange, but not far short of the ferry slips. As such the B815 never actually crossed the river - but Old Kilpatrick was the nearest place to its eastern end.
When the Erskine Bridge was opened and the ferry closed, the B815 was cut back to the new road and the eastern end renumbered A726.