A bigger road was completed in 1925, named the Great West Road (A 4), moving in much the same direction and forming the notional northern boundary of Isleworth. A six-lane dual carriageway for most of its length, with attendant cycle paths, it fulfilled the purpose of bypassing the bottlenecks of Brentford and Hounslow high streets to relieve the old road from London of traffic heading to and from Windsor and beyond. A later branch extension off this new road, named the Great South West Road, carried traffic south-westwards and this had the additional effect of relieving the London Road of traffic heading to and from Staines-upon-Thames and beyond.