A421 road Information (Geography)
|East end||A1 Black Cat Roundabout near St Neots|
|West end||A43 near Brackley|
The A421 is an important road for east/west journeys across south central England. Together with the A428, the A43 and A34, it forms the route from Cambridge through Milton Keynes to Oxford. The section between the A1 (near St Neots) and the A5 (in Milton Keynes) is a national primary route.
The road begins at the A1, just south of St Neots (and the junction with the A428 from Cambridge), at the Black Cat Roundabout. The road bypasses both Great Barford  and Bedford to the south to reach the M1 at junction 13. From there, it swings up through the southern part of Milton Keynes, doubling as the local grid road H8 Standing Way. During this time it crosses the A5 (and connects to it via a short spur which is part of the V6 Grafton Street).
Continuing westwards, as the route approaches Buckingham the road passes close by to the 14th century Thornborough Bridge, the only surviving mediaeval bridge in Buckinghamshire which was bypassed by the new bridge in 1974. Close to here, it then forms the Buckingham by-pass before joining the A43 ( Northampton — M40 junction 10) near Brackley. (On crossing the A43, the route due westward becomes the B4031 through Croughton, Aynho and Deddington to join the A361 to Chipping Norton).
The section from the A1 to the M1 is dual carriageway and fully grade-separated, with the section between Bedford and the M1 completed in December 2010,  winning the British Construction Industry Award in 2011. 
There is a short 3km section of single carriageway from the new flyover (beside Junction 13) to the south-eastern outskirts of Milton Keynes, where dual carriageway running resumes and continues as far as the southwestern outskirts. From here to the A43, the route is single carriageway, with the exception of the bypass around Tingewick.
The route of the A421 widening scheme, between the M1 Junction 13 and Kingston, Milton Keynes.
|Location||Central Bedfordshire, Milton Keynes|
|Proposer||Bedfordshire County Council|
|Cost estimate||£34.5 million|
|Start date||2014 (phase 1)|
|Supporters||Milton Keynes Council, Bedfordshire County Council|
In conjunction with the M1 widening schemes and dualling of the A421 between M1 Junction 13 and Bedford (see above), proposals were also put forward to widen the A421 between the M1 junction 13 Bedfordshire and the Kingston roundabout in Milton Keynes.  Exhibitions were held in June 2005 which rejected proposals to re-route the road in favour of widening the current road. In 2005 the project was given an estimated total cost of £33 million. 
Funding of GB£23.5 million was confirmed by the government for these works, as part of the South East Midlands Local Enterprise Partnership "Local Growth Deal".  As part of the government's pinch point reduction programme, in 2014 work commenced on the A421 in Milton Keynes to improve the Kingston roundabout. That work is now complete. The upgrade work for the final part of the A421, the section running from junction 13 to Kingston, started in September 2018 and is due to be complete by the end of 2020. 
The Oxford to Cambridge Expressway is a proposed grade-separated dual carriageway between the A34 near Oxford and the A14 near Cambridge, via (or near) Milton Keynes. The proposal aims to establish this route by linking existing roads and building new ones. The case for its creation is examined in a Strategic Study for the Cambridge – Milton Keynes – Oxford corridor, published by National Infrastructure Commission in November 2016.  The NIC sees the road as being of national strategic importance by providing an outer orbital route around London, linking Southampton, the M3, M4, M40, M1, A1, A14/M11 and Felixstowe.
This route will absorb the existing A421 and A428 roads between the A14 and the M1, with a new "greenfield" route from M1 J13 to the M40 and onwards to the A34, broadly in the East West Rail corridor. As of November 2019 [update], no announcement has been made on the precise route between the M1 and the A34, let alone the numbering of the route (A34, A421, even A428), although the M1 to M40 section is to be broadly parallel with the existing A421 and will replace it.
The A421 Tingewick bypass has a minor claim to fame as the location of the then fastest speeding incident ever recorded by British police, in March 2003.  Andrew Osborne, 31, of Leamington Spa, was filmed by a mobile speed camera while travelling at 157 miles per hour (253 km/h) on a motorcycle. His friend Neil Bolger, 30, of Gaydon, was clocked at 148 miles per hour (238 km/h). Both were convicted of dangerous driving, imprisoned for 28 days and banned from driving for two years (with a compulsory re-test). 
Blind Martine Brooks drove along the newly constructed A421 Great Barford Bypass (From the A1 Black Cat Roundabout to Bedford) and back to raise money for charity.  The drive took place two days before the official road opening, and she was accompanied by Frank Branston (Mayor of Bedford), Steve Clarke (Teacher and Navigator), and Denise Hubbard (Driving Instructor and Car Owner).
She reached a speed of 65 miles per hour (105 km/h) before doing a flawless three point turn, and returning to the A1.
- The Great Barford bypass opened on 24 August 2006.
- "A421 Bedford to M1 Junction 13". www.highways.gov.uk. 2011. Archived from the original on 15 December 2013. Retrieved 14 December 2013.
- "Winners 2011". www.bciawards.org.uk. 2011. Retrieved 14 December 2013.
- "A421 Miton Keynes to M1" (PDF). South East England Regional Assembly. Archived from the original (PDF) on 2 July 2010. Retrieved 22 July 2009.
- "Bedfordshire Local Transport Plan 2006/07 - 2010/11 - Major projects". Bedfordshire County Council. Archived from the original on 5 March 2016. Retrieved 9 December 2008.
- "£23.5million project unveiled to upgrade A421 to dual carriageway". Milton Keynes Citizen. 7 July 2014. Retrieved 27 January 2015.
- "Construction work begins to dual A421 in Milton Keynes". MK Web. 18 February 2014. Retrieved 27 January 2015.[ permanent dead link]
- "Oxford to Cambridge expressway strategic study: stage 3 report" (PDF). UK Department for Transport. 28 November 2016. Retrieved 3 August 2017.
- "Archived copy" (PDF). Archived from the original (PDF) on 1 October 2006. Retrieved 2006-07-21.CS1 maint: archived copy as title ( link) Thames Valley Police Annual Report 2003/04
- "A421 Great Barford Bypass Third Newsletter - August 2006" (PDF). Highways Agency. Archived from the original (PDF) on 5 June 2011. Retrieved 2008-12-29.
- The Great Barford (A421) Driving Challenge
- Highways Agency response to a query about widening the Berry Farm Underpass to allow for the canal (made under the 'Freedom of Information Act')