The Watford Gap is located at a minor gap between two slight hills in the county of Northamptonshire

Northamptonshire

Northamptonshire is a landlocked county in the English East Midlands, with a population of 629,676 as at the 2001 census. It has boundaries with the ceremonial counties of Warwickshire to the west, Leicestershire and Rutland to the north, Cambridgeshire to the east, Bedfordshire to the south-east,...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. Engineers from Roman times

Roman Britain

Roman Britain was the part of the island of Great Britain controlled by the Roman Empire from AD 43 until ca. AD 410.The Romans referred to the imperial province as Britannia, which eventually comprised all of the island of Great Britain south of the fluid frontier with Caledonia...

 onwards have found it to be an appropriate route connecting the Midlands

English Midlands

The Midlands, or the English Midlands, is the traditional name for the area comprising central England that broadly corresponds to the early medieval Kingdom of Mercia. It borders Southern England, Northern England, East Anglia and Wales. Its largest city is Birmingham, and it was an important...

 with the South East

South East England

South East England is one of the nine official regions of England, designated in 1994 and adopted for statistical purposes in 1999. It consists of Berkshire, Buckinghamshire, East Sussex, Hampshire, Isle of Wight, Kent, Oxfordshire, Surrey and West Sussex...

.

In a width of 400 metre (0.248549094659923 mi) the A5 road, the West Coast Main Line

West Coast Main Line

The West Coast Main Line is the busiest mixed-traffic railway route in Britain, being the country's most important rail backbone in terms of population served. Fast, long-distance inter-city passenger services are provided between London, the West Midlands, the North West, North Wales and the...

 railway, 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 a branch of the Grand Union Canal

Grand Union Canal

The Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...

 all traverse the gap in parallel.
An easy route between the 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...

 and Birmingham

Birmingham

Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...

 areas passes through or close to the small village of Watford, Northamptonshire

Watford, Northamptonshire

Watford is a village and civil parish in the Daventry district of the county of Northamptonshire in England. It should not be confused with the more significant town of Watford in Hertfordshire which is 50 miles to the south. At the time of the 2001 census, the parish's population was 224 people.It...

, located near Daventry

Daventry

Daventry is a market town in Northamptonshire, England, with a population of 22,367 .-Geography:The town is also the administrative centre of the larger Daventry district, which has a population of 71,838. The town is 77 miles north-northwest of London, 13.9 miles west of Northampton and 10.2...

 and Long Buckby

Long Buckby

Long Buckby is a village and civil parish in Northamptonshire, England, midway between Northampton and Rugby. In the 2001 census the parish of Long Buckby had a population of exactly 4,000....

.