One of the two main arterial roads into London from the West, the other being the A40 (Western Avenue). However, whereas the Western Avenue starts right at the edge of London, the key section of the A4 is really only from the [M4]? into the centre. The rest of the A4 is an important route in West London but is mirrored by the faster M4.
Traffic from the [M4]? elevated section is deposited after the Chiswick Roundabout onto Cedars Road in Chiswick This section consists of a series of upgraded suburban roads, fronted by houses much like the Western Avenue further north.
After this section the [Hogarth Roundabout]? is encountered. THis is a key junction for traffic joining from the southwestern arterial roads, and is a congestion blackspot. It is characterised by a sixties single-lane flyover from the southwest onto the Great West Road, which the A4 becomes after the junction. This then rises onto another sixties flyover, this time taking traffic over the Hammersmith gyratory system.
After dropping down from the flyover, the A4 runs next to the Piccadilly Line and District Line, rising again at West Kensington Station to pass over the West London Line and bring traffic to a screaming halt at Earl's Court, next to the attractive (more so than most) Tesco. After the junction with Earl's Court Road, the A4 turns into a rather precarious single carriageway road, the [Cromwell Road]?, with 2 or sometimes 3 lanes in each direction. It passes Sainsbury's and crosses Gloucester Road before reaching South Kensington and the Natural History Museum. The road progressively narrows from here on into the West End. As [Brompton Road]? it passes [Harrods]? and turns into Knightsbridge before reaching Hyde Park Corner.
After this only buses can traverse the A4 out of London along the Piccadilly bus lane, and drivers are subject to the congestion charge. After Green Park Station, it approaches Piccadilly Circus eastbound but uses [Pall Mall]? and St. James's St westbound. Finally it traverses Trafalgar Square, the Strand and the Aldwych, leaving [Fleet Street]? to approach its final destination, [Holborn Circus]?.
Traffic on the A4 is very heavy in rush hour. For drivers approaching London, if you can, it's much easier to come in by Tube - you can leave the M4 at junction 3 and take The Parkway south to get towards [Hatton Cross Station]? which is on the Piccadilly Line. A faster option might even be to leave the car at Reading. If you do need to use your car, then leave plenty of extra time and beware that traffic crawls from Hammersmith most of the way into London in the mornings, and vice versa particularly on Friday afternoons and Sunday evenings.
History: the route that is now the A4 (London to Bristol Trunk Route) is a pretty old coaching route, some of which coincides with Roman routes, too. However the section through Brentford and Chiswick was built new in around 1925 as an early bypass for the even then heavy congestion though Chiswick & Brentford High Streets. This newly opened stretch of road led to rapid ribbon development of industry through the Brentford section, which became know as the 'Golden Mile'. The old Smithkline Beecham building (now bought by Barrets for a housing development, but listed) and the Tarmac (now Carillion) building are typical of the architecture of the time.