A40
Holborn Viaduct carries the A40
Route information
Part of E30
Maintained by National Highways, English local authorities, South Wales Trunk Road Agent and North & Mid Wales Trunk Road Agent
Length	261.2 mi[1][2][3] (420.4 km)
Major junctions
East end	A1 / A1121 in City of London
Major intersections	see also: A40 road (London) A5 in Greater London M40 in Greater London A34 / A44 near Oxford M5 near Cheltenham A38 in Gloucester A48 near Gloucester A49 at Bridstow
West end	Goodwick (Fishguard)
Location
Country	United Kingdom
Counties	England: Greater London, Buckinghamshire, Oxfordshire, Gloucestershire, Herefordshire Wales: Monmouthshire, Powys, Carmarthenshire
Primary destinations	London, Beaconsfield, High Wycombe, Oxford, Cheltenham, Gloucester, Ross-on-Wye, Monmouth, Abergavenny, Brecon, Llandovery, Llandeilo, Carmarthen, Haverfordwest, Fishguard
Road network
Roads in the United Kingdom Motorways A and B road zones
← A39 → A41

The A40 is a trunk road which runs between London and Goodwick (Fishguard), Wales, and officially called The London to Fishguard Trunk Road (A40) in all legal documents and Acts. Much of its length within England has been superseded by motorways, such as the M40, and has lost its trunk road status, though it retains it west of Gloucester, including its length within Wales. It is approximately 260 miles (420 km) long. The eastern section from Denham, Buckinghamshire to Wheatley, Oxfordshire is better served by the M40 and its former function of linking London with Cheltenham and Gloucester has been taken by the M4, A419 and A417 via Swindon.

The A40 1923 route was from the City of London to Fishguard. The road still begins and ends in the same places, but a number of changes have been made to its route.^[4]

The first change dates from 1935, between Ross-on-Wye and Abergavenny. The original route of the A40 was via Skenfrith, avoiding Monmouth; this road was renumbered the B4521. The A40 was rerouted via Raglan; between Ross and Raglan it replaced part of the A48, between Raglan and Llanvihangel-nigh-Usk it replaced the B4234, and between Llanvihangel and Abergavenny it replaced part of the A471.

Subsequently, the A40 was rerouted within west London. Western Avenue dates from the 1930s, but was originally opened as the A403. After the Second World War, the A40 was rerouted along part of the A219 (west of Notting Hill) and Western Avenue. The old route (via Acton, Ealing, Southall, Hayes, Hillingdon and Uxbridge) was renumbered the A4020.

Initially, the A40 went through the centre of Oxford, via Headington, Magdalen Bridge, the High Street, Carfax and Botley, and over the Swinford Toll Bridge to Eynsham. It was rerouted in the 1930s to follow the first section of the Oxford Ring Road to the north of the city, and then followed a direct line to bypass Eynsham. The old route became part of the A420 to Botley, and the section between Botley and Eynsham was renumbered the A4141,^[5] renumbered again in the 1960s to the B4044.

In central London it is High Holborn and then Oxford Street. At Marble Arch it joins the A5 Edgware Road as far as the Marylebone Flyover to become Westway (classified A40(M) as an elevated motorway) then meets Western Avenue. For the greater part, this section is six lanes, otherwise four lanes. With two exceptions, Western Avenue forms a grade-separated motorway standard dual-carriageway between Paddington and the M40 motorway. The two at-grade intersections are Gypsy Corner and Savoy Circus; both of which are traffic light controlled. At Denham Roundabout, the six lane Western Avenue flows into the M40.

The A40 branches off the Denham roundabout to run as a dual carriageway. After the junction with the A413, the A40 follows the same route as the M40 as a single carriageway, passing through Beaconsfield and High Wycombe. Beyond Stokenchurch the road is much quieter; when meeting the B4009 and A329 those roads have priority. Approaching Oxford, the A40 becomes a busy dual carriageway, carrying traffic from the M40 to Oxford and beyond. The road forms the northern section of the Oxford Ring Road, crossing the A44 and the A34. In Oxford, it passes the Thornhill Park and Ride, where the OxfordTube, The Airline to Heathrow & Gatwick, & Oxford Park and Ride buses stop.

The A40 passes under the A34, reverting to single carriageway for 10 miles (16 km) until the dual carriageway just east of Witney with a grade-separated junction. The dual carriageway finishes at a roundabout. For the rest of Oxfordshire and Gloucestershire until Cheltenham, other than for a few short stretches, the road is single carriageway. A height of 820 feet (250 m) above sea level is located 3 miles (4.8 km) west of the A429 junction. Before Andoversford the A436 breaks off to the west to try to take traffic away from descending into the centre of Cheltenham itself. The road travels through Cheltenham town centre along at least two parallel routes (neither is part of a one-way system: Sandford Road and Montpellier Terrace make up one part, Thirlestaine Road and Suffolk Road the other). Becoming a dual carriageway, it passes GCHQ in Cheltenham and the three-level stacked roundabout junction with the M5 motorway. In February 2015, the Witney Oxford Transport Group proposed the reopening of Yarnton railway station as an alternative to improvements to the A40 road proposed by Oxfordshire County Council.^[6][7]

The A40 is the Gloucester bypass, most of which is dual carriageway. The junction with the A48 to Chepstow is at Highnam. For the remainder of Gloucestershire, and a part of Herefordshire, the road is single carriageway until Ross-on-Wye. There it connects with the M50 motorway, and forms part of the high quality dual carriageway between South Wales and the English Midlands. From Ross-on-Wye to Monmouth the road follows the Wye Valley, an Area of Outstanding Natural Beauty, crossing the Wales–England border a mile east of Monmouth. Just west of Monmouth are twin tunnels; these are the only tunnels on the A40. Near Raglan, the A40 has a grade separated junction with the A449. The A40 continues as a dual carriageway to Abergavenny.

At Abergavenny is the A40 junction with the Heads of the Valleys road, (A465) and the A4042. Now the A465 becomes the primary route between the Midlands to the South Wales Valleys and Swansea; there is a dual-carriageway route to Carmarthen via the A465, M4 and A48.

The A40 becomes single carriageway and continues through Abergavenny, following the north side of the Usk valley through the eastern part of the Brecon Beacons National Park until Brecon. At Bwlch between Abergavenny and Brecon, the A40 is 660 feet (200 m) above sea level. The A40 is dualled for over 1.5 miles (2.4 km) as it approaches a junction east of Brecon with the A470 north, which is the main north–south road through mid-Wales. Continuing as a dual carriageway, the A40 and A470 concurrent bypass Brecon to the south, crossing the River Usk here. At the western end of the bypass is a further junction with the A470 south. Beyond this point the A40 continues as a single carriageway, now south of the River Usk, and roughly follows the northern edge of the Brecon Beacons National Park. A height of 820 feet (250 m) above sea level is located less than 1 mile (1.6 km) east of Trecastle. In Llandovery the road crosses the Heart of Wales railway and the River Tywi; the road, railway and river then run parallel until Llandeilo, where the National Park ends and the railway turns south. The A40 continues west along the Tywi valley to Carmarthen where as a dual carriageway it forms the eastern bypass, meeting the terminus of the A48 at Pensarn. Here the A40 returns to being a primary route westwards.

At Carmarthen the A40 crosses the River Tywi twice with two 90-degree junctions and continues on 10 miles (16 km) of dual carriageway as far as St. Clears, where the dual carriageway ends at the junction with the A477 trunk road. Now the A40 is a mixture of 2 or 3 lane single-carriageway to Haverfordwest and Fishguard. This section of road is controlled by the Welsh Government (formerly 'Welsh Assembly Government'), which describes it as "one of the lowest standard sections of the Trans European Road Network in the United Kingdom".^[8]

St Clears to Haverfordwest dualling There were plans in 2002 for a major improvement of the 23-mile stretch between St Clears and Haverfordwest which included upgrading to a dual carriageway; described as an extension of the national motorway network to the West Wales coast by virtue of the route from the M4 motorway being entirely dual carriageway.^[9] The £60 million scheme was subject to a European Environmental Assessment. Within a couple of years, the project appeared to be dying a very quiet death, causing local newspapers to report it being an election stunt for the two marginal constituencies that would best benefit from the improvements. The following Welsh elections saw both constituencies change the party of majority. The political party at the centre of the row instead directed the project deferment to damning environmental statements by Friends of the Earth Cymru.^[10][11] The scheme was officially scrapped in 2008 after a Welsh Assembly committee decided to abandon the proposals. Instead, it recommended upgrades to the existing route including bypasses around Robeston Wathen and Llanddewi Velfrey using a three-lane option. This was welcomed by the Friends of the Earth, saying "The dual carriageway on the A40 would increase traffic levels, increase the emission of greenhouse gases, it would be harmful for the environment, it would be hugely expensive. That money would be better spent on improving public transport, on health, on education, there's no need for it. We think the assembly committee has come to the right decision".^[12]

Whitland Bypass The last improvement to the A40 on this section prior to the Welsh Assembly Government having the devolved responsibility for this road was a 4.1 kilometres (2.5 mi) £8 million bypass around Whitland. Constructed in 1994, the road started east of Black Bridge on the original A40, then running north of the town before to a new roundabout just west of Llain Cottage. The Secretary of State for Wales was asked a written question by Rhodri Morgan about adding a second carriageway to the Whitland bypass scheme, to which John Redwood replied "There are no proposals to add a second carriageway to the Whitland bypass. The design capacity of a single carriageway two-lane highway is more than adequate to cater with the anticipated traffic flows for the foreseeable future."^[13]

Llanddewi Velfrey Bypass A new bypass has been granted approval by the Welsh Assembly Government at Llanddewi Velfrey in Pembrokeshire. The scheme would improve the A40 between Llanddewi Velfrey and Penblewin, to the west of St Clears and meet the aim of the targeted investment in infrastructure along the east–west road corridor in south Wales.^[14] From the east, it is proposed that a roundabout would be created just north of Glenfield Farm, where the straight section from St Clears ends at Bethel Chapel, and then take a new route north-west of the town of Llanddewi Velfrey, south-west over Pentroydin Fawr and Penttroydin Fech farms with cattle underpasses, a new underpass beneath the existing Llanddewi Velfrey to Llanfallteg road, before going over the original A40 at Ffynnon Wood. To the west of Ffynnon Wood, the road would then cross back over the original A40 to the east of Henllan Lodge in a way to maintain the tree lined avenue to Henllan, then run parallel to the A40 on the north side of the existing A40 to a new roundabout at Penblewin and the junction with the A478.^[15]

This was originally known as the Blue and Purple routes during the Consultation in 2006^[16] for which 75% preferred the blue route, and only 20% preferred the red route. 54% felt the section from Ffynnon Wood and Penblewin Roundabout needed improvement, with both orange and purple routes preferred by 42% of the respondents. Welsh Water/Dwr Cymru expressed concerns with the red route affecting water mains and sewers, and Henllanfallteg Community Council felt the red route would not improve the quality of life in Llanddewi Velfrey. Pembrokeshire County Council expressed concerns that the route planned was a single carriageway, and that within seven years, a dual carriageway would be required.

Robeston Wathen Bypass A new bypass has been constructed between Penblewin and Slebech Park making the road straighter and with a '2+1' road layout to help improve overtaking opportunities.^[17]

Starting to the west of Toch Lane (approx. 2 kilometres (1.2 mi) east of Slebech), the route travels eastwards for 4.6 kilometres (2.9 mi), passing 200 metres (660 ft) south of Robeston Wathen, and ending 0.5 kilometres (0.31 mi) east of the village, just west of Flimstone Lane.

Construction started on the route in February 2009, with the works completed and the new road opening 1 March 2011. The road was built by Costain. The scheme was nearly £14 million over the initial budget of £27.6 million, eventually costing £41.4 million. The Welsh Assembly Government explains this increase as being the result of inflation and land costs, saying the original budget did not include either, as well as additional statutory procedures, additional works following some design standards, and the increase in VAT.^[18]

The Kell The Kell is located on a section of the A40 that forms a north–south corridor between Fishguard, 17 kilometres (11 mi) to the north and Haverfordwest, 7.5 kilometres (4.7 mi) to the south, close to Treffgarne and Spittal. The improvement saw about 0.48 kilometres (0.30 mi) of new trunk road commencing at a point on the trunk road approximately 622 metres south of the centreline of the junction of the A40 trunk road with the C3059 road to Spittal and extending in a generally northerly direction to a point approximately 112 metres south of the junction of the trunk road with the C3059 road to Spittal.^[19] This resulted in the road being rerouted through pasture to the east of the original road, taking a right hand bend about 160 metres (520 ft) south of The Old Mill, taking a 5.5% gradient, and rejoining the original road 210 metres (690 ft) north of The Kell. The original road has subsequently been converted to an access road for The Old Mill, Beavers Lodge and The Kell, accessing the new road at The Old Mill.

Fishguard Bypass The Fishguard Bypass was planned to provide a more direct route with greater capacity to the Port of Fishguard at Goodwick avoiding the town centre of Fishguard. It was constructed during the late 1990s and opened in 2000. It takes the form of a three-lane carriageway on an approx. 10% gradient around the western edge of Fishguard. It runs from its highest point at Rafael roundabout 1 km south of Fishguard town in a generally northerly direction to its lowest point at Windy Hall roundabout where it rejoins the old A40 route at Gasworks Hill. The bypass is concurrent with a section of the A487 trunk road with the A40 dominant.^[20][21]

County	Location	mi[1] [2] [3]	km	Destinations	Notes
Greater London	City of London	0.0	0.0	Goswell Road (A1 north) / London Wall (A1121 east) – Angel, Islington	Eastern terminus; southern terminus of A1; western terminus of A1211
	City of London-Camden boundary	0.6	0.97	New Fetter Lane (A4 west) / Hatton Garden (B521) / Charterhouse Street	Eastern terminus of A4
	Camden	1.2	1.9	Theobalds Road (A401 east)	Eastern terminus of A401 concurrency
		1.3	2.1	Kingsway / Southampton Row (A4200)	No access from A40 east to A4200, from A4200 south to A40, or from A4200 north to A40 east
	Camden-Westminster boundary	1.6– 1.7	2.6– 2.7	A400 (Bloomsbury Street / Tottenham Court Road / Charging Cross Road) / Shaftesbury Avenue (A401 west) / A501 – Camden Town, West End, Westminster	West End and Westminster signed westbound only; western terminus of A401 concurrency
	Westminster	2.2	3.5	Regent Street (A4201)	No right-hand turns
		2.7	4.3	Orchard Street (A41 west) / North Audley Street	Eastern terminus of A41
		2.8	4.5	Portman Street (A4380 north) / Park Street	Southern terminus of A4380
		3.0	4.8	Ring Road south (Park Lane / A4202 south) / A402 west (Bayswater Road) to A4 / A3 – Westminster, Notting Hill, Knightsbridge, Victoria	Knightsbridge and Victoria signed westbound only; eastern terminus of A5 / Ring Road concurrency; southern terminus of A5; eastern terminus of A402
		3.1	5.0	Wigmore Street (A5204 east) / Seymour Street	No access from A40 to A5204; western terminus of A5204
		3.5	5.6	Old Marylebone Road (A501 east) / Sussex Gardens (A4209 south-west)	No access from A40 to A501, from A40 east to A4209, from A501 to A40 west, or from A4209 to A40 east; north-eastern terminus of A4209
		3.6	5.8	A40 jumps from concurrency with A5 to the Westway without any direct connection^
		4.7	7.6	To Ring Road south - West End, Paddington	Grade-separated junction; eastbound exit and westbound entrance
	Kensington and Chelsea-Hammersmith and Fulham borough boundary	6.0– 6.3	9.7– 10.1	A3220 south – Hammersmith, Shepherd's Bush, Earl's Court, Westminster	Grade-separated junction; Westminster signed eastbound only
	Hammersmith and Fulham	6.5	10.5	A219 – Harlesden, White City	Grade-separated junction; Eastbound exit and westbound entrance
	Ealing	8.1– 8.3	13.0– 13.4	A4000 / B4492 – Harlesden, Willesden, Acton, Park Royal
		9.5	15.3	Park Royal (central)	Grade-separated junction; eastbound exit only
		9.4– 10.0	15.1– 16.1	A406 (North Circular) / M1 / M4 / A41 / A1 – Wembley, Ealing
		10.9– 11.5	17.5– 18.5	Perivale	Grade-separated junction
		11.9– 12.3	19.2– 19.8	A4127 – Harrow, Sudbury, Greenford	Grade-separated junction
		13.3– 13.9	21.4– 22.4	A312 – Heathrow Airport, Hayes, Southall, Yeading, Northolt	Grade-separated junction; Heathrow, Hayes, Southall and Yeading signed westbound only, Northolt eastbound only
	Hillingdon	14.4– 14.9	23.2– 24.0	A4180 – Ruislip, Heathrow Airport, Hayes, Southall, Yeading	Grade-separated junction; Ruislip signed westbound only, Heathrow, Hayes, Southall and Yeading eastbound only
		16.3– 17.2	26.2– 27.7	A437 / B466 – Hillingdon, Ruislip, Ickenham	Grade-separated junction
		17.5– 17.9	28.2– 28.8	B467 – Uxbridge, Harefield, Ickenham, Ruislip	Grade-separated junction; Ruislip signed eastbound only
Buckinghamshire	Denham	18.5– 19.1	29.8– 30.7	M40 north-west to M25 – Oxford, Birmingham, Beaconsfield, Watford A4020 east (Oxford Road) – Uxbridge, Denham A412 south (Denham Road) – Slough	Birmingham and Beaconsfield signed westbound only, Watford eastbound only; eastern terminus of A412 concurrency; western terminus of A4020
		19.7	31.7	A412 north (Denham Avenue) – Rickmansworth, Higher Denham, Denham Green	Western terminus of A412 concurrency
		20.6	33.2	A413 north (Amersham Road) – Amersham, The Chalfonts	Southern terminus of A413
	Beaconsfield	25.5	41.0	A355 to M40 / M25 – Heathrow Airport, Slough, Amersham, London, Wycombe	London and Wycombe signed westbound only
	Loudwater	28.7	46.2	M40 east – London, Flackwell Heath A4094 south – Maidenhead, Bourne End, Wooburn Green	Flackwell Heath signed westbound only; M4 junction 3; northern terminus of A4094
	High Wycombe	31.7	51.0	A404 to M4 / M40 – Maidenhead, Marlow, Amersham
		32.1	51.7	A4128 north (Arch Way) – Great Missenden	Southern terminus of A4128
	High Wycombe-West Wycombe boundary	33.5	53.9	A4010 south (Chapel Lane) to M40 / A404 – Marlow	Information signed eastbound only; eastern terminus of A4010 concurrency
	West Wycombe	34.1	54.9	A4010 north (Bradenham Road) – Aylesbury, Princes Risborough	Western terminus of A4010 concurrency
Oxfordshire	Great Haseley-Great Milton-Tiddington-with-Albury boundary	47.6	76.6	A329 (Rycote Lane) to M40 south – London, Wycombe, Wallingford, Thame, Stadhampton, Moreton	Brief concurrency
	Great Milton-Tiddington-with-Albury boundary	49.1	79.0	A418 north-east (Oxford Road) – Aylesbury, Tiddington	Tiddington signed eastbound only; south-western terminus of A418
		49.7– 50.3	80.0– 81.0	M40 – London, High Wycombe, Birmingham, Banbury	M40 junctions 8-8A
	Wheatley	51.9	83.5	Wheatley, Holton, Waterperry	Grade-separated junction; no westbound exit
	Headington	54.6	87.9	A4142 south (Ring Road) / A420 west (London Road) / Bayswater Road – City centre, Cowley, Headington, Barton	Northern terminus of A4142; eastern terminus of A420
	Marston	56.3	90.6	Marston, Elsfield	Grade-separated junction
	Cutteslowe	58.3	93.8	A4165 (Banbury Road) – Summertown, Kidlington, Gosford
		58.7	94.5	A44 west (Ring Road) / Woodstock Road (A4144 south) / Five Mile Drive to A34 / M40 / A420 – Midlands, Evesham, Newbury, Oxford city centre, Wolvercote, Oxford Airport	Swindon signed eastbound only; eastern terminus of A44; northern terminus of A4144
	South Leigh-Witney boundary	66.2	106.5	B4022 – Witney East	Grade-separated junction; westbound exit and eastbound entrance
	Witney-Ducklington boundary	68.0– 68.4	109.4– 110.1	A415 to A4095 – Witney, Abingdon, Faringdon	Grade-separated junction; To A4095 and Faringdon signed westbound only
	Brize Norton-Minster Lovell boundary	70.8	113.9	B4477 – Carterton, RAF Brize Norton, Minster Lovell	Grade-separated junction; westbound exit and eastbound entrance
	Burford	74.8	120.4	A361 (The Hill) to A424 – Lechlade, Chipping Norton, Stow, Burford, Faringdon	Faringdon signed eastbound only
Gloucestershire	Northleach with Eastington-Hampnett boundary	83.9	135.0	A429 – Cirencester, Stow, Northleach, Bibury, Turkdean, Bourton
	Shipton	89.9	144.7	A436 west / Shipton to A417 – Gloucester, Kilkenny	Eastern terminus of A436 concurrency
	Andoversford	90.7	146.0	A436 east – Stow-on-the-Wold, Bourton-on-the-Water	Western terminus of A436 concurrency
	Charlton Kings-Cheltenham boundary	95.8	154.2	A435 south (Cirencester Road) / Haywards Road – Cirencester, Seven Springs, Colesbourne	Information signed eastbound only; eastern terminus of A435 concurrency
	Cheltenham	96.1	154.7	A435 north (London Road) to B4632 – Cheltenham town centre, Evesham, Broadway, Prestbury, Winchcombe	Information signed westbound only; western terminus of A435 concurrency
		97.0	156.1	A46 (Bath Road) – Stroud, Leckhampton, Shurdington, Birdlip
		98.8	159.0	Princess Elizabeth Way (A4013 north) - Swindon Village	Southern terminus of A4013
	Badgeworth–Churchdown boundary	100.1– 100.7	161.1– 162.1	M5 – The South West, Midlands, Tewkesbury, Bristol	The South West and Midlands signed westbound only; Tewksbury and Bristol eastbound only; M5 junction 11
	Gloucester			A417 south-east / B4063 (Cheltenham Road) – Cirencester, Hucclecote, Longlevens, Churchdown, Innsworth	Airport signed eastbound only
		104.5	168.2	A38 (Tewksbury Road) – Gloucester, Tewkesbury, Twigworth, Longford
		105.8	170.3	A417 to M50 – Ledbury, Gloucester, Hartpury, Maisemore
	Highnam	107.3	172.7	A48 west – Chepstow, Westbury-on-Severn, Minsterworth	Eastern terminus of A48
	Huntley	112.3	180.7	A4136 west (Longhope Road) to A466 – Monmouth, Chepstow, Cinderford, Mitcheldean	To A466, Monmouth, and Chepstow signed westbound only; eastern terminus of A4136
Herefordshire	Ross-on-Wye	121.4	195.4	A449 north / Ledbury Road to M50 – Midlands, Worcester, Ross-on-Wye	Eastern terminus of A449 concurrency
	Wilton	122.8	197.6	A49 north / B4260 (Wilton Road) – Hereford, Ross-on-Wye, Wilton	Wilton signed eastbound only; southern terminus of A49
	Whitchurch	127.6– 127.7	205.4– 205.5	A4137 to B4229 – Hereford, Goodrich, Symonds Yat (east)	Grade–separated junction; southern terminus of A4137
Herefordshire–Monmouthshire county boundary	Ganarew–Monmouth boundary	130.5	210.0	England–Wales border
Monmouthshire	Monmouth	131.8– 132.4	212.1– 213.1	A466 to A4136 – Monmouth, Chepstow, Forest of Dean
		132.9	213.9	B4293 to B4233 – Monmouth, Trellech, Rockfield	Grade-separated junction; To B4233 and Rockfield signed westbound only; no westbound entrance
	Mitchel Troy–Raglan boundary	138.8– 139.2	223.4– 224.0	A449 south to M4 – Newport, Cardiff	Grade-separated junction; Cardiff signed westbound only; western terminus of A449 concurrency
	Llanfoist Fawr–Abergavenny boundary	147.6– 147.9	237.5– 238.0	A465 (Heads of the Valleys Road) / A4042 south – Merthyr Tydfil, Hereford, Newport, Pontypool	Pontypool signed westbound only; northern terminus of A4042
	Abergavenny	149.5	240.6	A4143 south / MT Street to A465 – Llanfoist, Merthyr	Northern terminus of A4143
Powys	Crickhowell	155.2	249.8	A4077 south (New Road) – Llangattock, Gilwern	Northern terminus of A4077
	Cwmdu	156.7	252.2	A479 north to A470 – Builth Wells, Tretower, Cwmdu, Talgarth	Southern terminus of A479
	Llanfrynach	166.7	268.3	Llanfrynach, Groesffordd, Llangors, Pencelli	Grade–separated junction
	Brecon	167.4	269.4	A470 north / B4601 – Builth Wells, Brecon	Eastern terminus of A470 concurrency
		169.8	273.3	A470 south / B4601 – Cardiff, Llanfaes	Western terminus of A470 concurrency
	Sennybridge	177.2	285.2	A4067 south – Ystradgynlais, Swansea	Northern terminus of A4067
Carmarthenshire	Llandovery	189.7	305.3	A4069 south (Broad Street) – Llangadog	Northern terminus of A4069
		189.9	305.6	A483 north (New Road) – Builth Wells	Eastern terminus of A483 concurrency
	Llanwrda	193.9	312.1	A482 north-west – Lampeter, Pumsaint	South-eastern terminus of A482
	Llansadwrn	196.3	315.9	A4069 (Station Road) – Llangadog, Brynamman, Bethlehem
	Manordeilo and Salem	201.5	324.3	A483 south (Rhosmaen Street) to M4 – Llandeilo, Swansea	Western terminus of A483 concurrency
	Carmarthen	214.8	345.7	A485 north to A484 – Lampeter, Cardigan	Southern terminus of A485
	Llangunnor	216.2	347.9	A484 north / B4300 (Heol Llangynnwr) – Carmarthen town centre, Llangunnor	Eastern terminus of A484 concurrency
		216.7	348.7	A48 east / A484 south to M4 – Swansea, Llanelli, Burry Port, Kidwelly	Western terminus of A484 concurrency; western terminus of A48
	Carmarthen	217.2	349.5	A4242 east – Town centre	Western terminus of A4242
		217.6– 217.8	350.2– 350.5	B4312 – Johnstown	Grade-separated junction; no eastbound exit
		218.4– 218.5	351.5– 351.6	Llanllwch to B4312 – Johnstown	Grade-separated junction; To B4312 and Johnstown signed eastbound only
	St Clears	225.5– 225.9	362.9– 363.6	A477 west / A4066 south to A478 – Pembroke Dock, St Clears, Laugharne, Pendine, Tenby	To A478 and Tenby signed westbound only; eastern terminus of A477; northern terminus of A4066
Pembrokeshire	Llanddewi Velfrey–Narberth boundary	235.9	379.6	A478 – Cardigan, Narberth
	Llawhaden	239.3	385.1	A4075 south / B4314 to A477 – Pembroke Dock, Tenby, Robeston Wathen, Llawhaden	Northern terminus of A4075
	Haverfordwest	246.2– 247.4	396.2– 398.2	A487 north / A4076 south – Town centre, Milford Haven, St Davids	St Davids signed westbound only; southern terminus of A487; northern terminus of A4076
	Scleddau	258.8	416.5	A4219 north to A487 – St Davids	Southern terminus of A4219
	Fishguard and Goodwick	260.0– 261.2	418.4– 420.4	A487 – Fishguard, Cardigan, St Davids	Western terminus
	1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Incomplete access

• 
  High Holborn
• 
  New Oxford Street
• 
  Marble Arch
• 
  The Hoover Building on A40 was a Tesco supermarket and is now apartments
• 
  A40 at Monmouth
• 
  Western end of A40 at Goodwick

• British road numbering scheme
• Trunk roads in Wales

• Edward Platt, Leadville: A Biography of the A40 (Picador, 2001). ISBN 0-330-39263-8.

51°52′42″N 2°01′51″W / 51.87824°N 2.03084°W / 51.87824; -2.03084