Glen Roundabout lies on the A8 in the west end of Port Glasgow, near the Greenock boundary, on the south bank of the Clyde. It is one of three roundabouts that were built when the A8 was realigned around what is now Port Glasgow Retail Park in 2006. It is located where the old and new lines of the A8 through west Port Glasgow meet.
The roundabout is a fairly simple 3 arm roundabout, with the A8 turning around 90 degrees from south to west, where it closely parallels the Gourock Branch of the Inverclyde Line railway for around 400m to Bogston station. The other arm is the now unclassified Brown Street, now singled having been the A8 dual carriageway until the new road opened. The even earlier A8, Ardgowan Street passes under the current A8 at 90 degrees immediately north of the roundabout.