A key part of the project was the construction of the "missing link", a short line of track that would have connected the existing Metropolitan line to the former British Rail Croxley Green branch line at their closest point; this would have been achieved by a new junction near Baldwins Lane, about 1.0 kilometers northeast of Croxley station and a viaduct and a bridge to carry the Metropolitan line over the A412 Watford Road dual carriageway and the Grand Union Canal to the former BR line.