The A5183 road is a de-trunked section of the A5. It covers the section between Junction 9 of the M1 motorway

M1 motorway

The M1 is a north–south motorway in England primarily connecting London to Leeds, where it joins the A1 near Aberford. While the M1 is considered to be the first inter-urban motorway to be completed in the United Kingdom, the first road to be built to motorway standard in the country was the...

 and Edgware

Edgware

Edgware is an area in London, situated north-northwest of Charing Cross. It forms part of both the London Borough of Barnet and the London Borough of Harrow. The area is identified in the London Plan as one of 35 major centres in Greater London....

 in north London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, largely along Watling Street

Watling Street

Watling Street is the name given to an ancient trackway in England and Wales that was first used by the Britons mainly between the modern cities of Canterbury and St Albans. The Romans later paved the route, part of which is identified on the Antonine Itinerary as Iter III: "Item a Londinio ad...

. The renumbering was to prevent drivers of heavy southbound vehicles assuming that a low number '5' indicated a superior quality road which this stretch is not as it is narrow in many places.

The main beneficiary of this renumbering is the city of St Albans

St Albans

St Albans is a city in southern Hertfordshire, England, around north of central London, which forms the main urban area of the City and District of St Albans. It is a historic market town, and is now a sought-after dormitory town within the London commuter belt...

 that used to be 'host' to both the A5 and the A6. A similar subterfuge has been made with that part of the A6, which is now renumbered to the A1081 road

A1081 road

The A1081 road in Hertfordshire, England broadly follows and replaces the former route of the A6 south of Luton in Bedfordshire.It runs from Luton Airport south via Harpenden to St Albans and then bears southeast via London Colney to High Barnet, where it meets the A1000 .The route was renumbered...

.

A bypass has been built around the small town of Redbourn

Redbourn

Redbourn is a village and civil parish in Hertfordshire, United Kingdom, lying on Watling Street, 3 miles from Harpenden, 4 miles from St Albans and 5 miles from Hemel Hempstead. It has a population of around 6,000.-History:...

. The former route of the A5 can still be seen passing through the middle of the town, now reduced to an unclassified road.