A roundabout interchange is a type of interchange between a controlled access highway, such as a motorway or freeway, and a minor road. The slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges.
A roundabout interchange is similar to a rotary interchange, which uses a rotary rather than a roundabout. Roundabouts may also be used in conjunction with other interchange types such as a standard or folded diamond interchange, but such use should not be confused with a roundabout interchange.
Roundabout interchanges are extremely common in the United Kingdom and Ireland with hundreds on the motorway network alone. However, recent cost cutting has meant that dumbbell interchanges are increasingly used instead. These are essentially diamond interchanges with roundabouts instead of signals or stop signs where the slip roads meet the minor road. They are cheaper than roundabout interchanges as only one bridge is required instead of two.
Roundabout interchanges are much less common in North America but have been built more frequently since 1995, to improve safety, and to reduce traffic delays and bridge widening costs. However, many of the older and more dangerous rotary-style overpass interchanges have been signalized to improve throughput and safety, such as the former Drum Hill Rotary (now Drum Hill Square) in Chelmsford, Massachusetts, in New England, where such interchanges are unusually common.
A divided diamond, in which the minor road is separated into four intersections, rather than two, also acts like a roundabout interchange, but it is more square in shape and, typically, has traffic light control.
The three-level stacked roundabout is a variation on the roundabout interchange in which both roads are grade-separated. It is similar to the three-level diamond interchange except that the small square of that latter interchange is enlarged to a true roundabout. If the roundabout is sufficiently large, the interchange may require only two levels. [1]
Three-level stacked roundabouts are quite common in Britain because they use less land than other four-way junctions where both roads are grade separated. However, they have lower capacity for turning movements – some have had direct-linking slip roads added later in an attempt to solve this problem. Examples of such junctions are found at Lofthouse, West Yorkshire (M1/M62; 53°43′55″N1°30′47″W / 53.73194°N 1.51306°W ) and Swanley, Kent (M20/M25; 51°23′19″N0°11′38″E / 51.38861°N 0.19389°E ).
A roundabout, also known as a rotary or traffic circle, is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.
The M4, originally the London-South Wales Motorway, is a motorway in the United Kingdom running from west London to southwest Wales. The English section to the Severn Bridge was constructed between 1961 and 1971; the Welsh element was largely complete by 1980, though a non-motorway section around Briton Ferry bridge remained until 1993. On the opening of the Second Severn Crossing in 1996, the M4 was rerouted over it.
The M40 motorway links London, Oxford, and Birmingham in England, a distance of approximately 89 miles (143 km).
The M2 is a 26-mile (42 km) long motorway in Kent, England, and was built to bypass a section of the A2 road in Kent, which goes through the Medway Towns, Sittingbourne, and Faversham. It provides an alternative route to the Port of Dover, which supplements the M20 motorway located further to the south. The terminal junctions of the M2 intersect with the A2, which come together to form a 62-mile (100 km) long trunk road from London to Dover.
The M180 is a 25.5-mile (41 km) motorway in eastern England, starting at junction 5 on the M18 motorway in Hatfield, within the Metropolitan Borough of Doncaster, South Yorkshire, and terminating at Barnetby, Lincolnshire, some 10 miles (16 km) from the port of Immingham and 14 miles (23 km) from the port of Grimsby. The A180 road continues to the east for Grimsby, Cleethorpes and Immingham. Scunthorpe, Lincoln, Hull, Brigg, Bawtry and the Isle of Axholme can be accessed using the motorway. Humberside Airport, the now-closed Doncaster Sheffield Airport, and the Killingholme, Humber and Lindsey oil refineries are close to the motorway. The road forms part of the unsigned Euroroute E22 and is the main route along the south bank of the Humber Estuary.
The M271 is a 3-mile (4.8 km) long motorway near Southampton in Hampshire, England. Construction began in 1973 and it opened in 1975. It provides part of the route to Southampton Docks from the M27, which in turn makes up another part of the route to the docks from the nearby M3 Motorway.
The Denham Roundabout is a road junction in Denham, Buckinghamshire. It was originally opened in 1943 in conjunction with the completion of the new Western Avenue route into west London. The Western Avenue took over the classification of the A40, with the previous route to London, via Uxbridge and Ealing, being reclassified as the A4020. The roundabout also included a new link to A412 that formed part of the outer London orbital route.
The A194 road is a road in Tyne and Wear, England. It runs northeast from its start at junction 65 of the A1(M) near Washington, and the first 3 miles (4.8 km) are motorway standard, designated the A194(M). There are intermediate junctions with the A182 and the A195 before the motorway section ends at the A184 junction. The junctions were unnumbered until 2013 when they were designated J1 to J3.
The West Cross Route (WCR) is a 0.75 mile segment of dual carriageway of the A3220 route in West London running north–south between the northern elevated roundabout junction with the western end of Westway (A40) and the southern Holland Park Roundabout. It runs through Shepherd's Bush to its west and Notting Hill to its east.
The A1058, known locally as the Coast Road, is a major road in Newcastle upon Tyne and the adjoining borough of North Tyneside in the North East. It runs from the Newcastle Central Motorway to the coast, terminating between Whitley Bay and Tynemouth. From west to east it connects Newcastle city centre with Jesmond, Heaton, Wallsend, Battle Hill, Howdon, Meadow Well, North Shields, Whitley Bay and Tynemouth. The road has existed since December 1924, when it was opened by then-transport minister Wilfrid Ashley.
The A405 is a 4.8 miles dual carriageway road in Hertfordshire, England, from the A41 at Leavesden Green, near Watford, to the A414 at Park Street Roundabout near St Albans.
The A412 is a road in England between Slough and Watford. It was the main artery for this corridor and used to continue to St Albans prior to the construction of the M25. It provides interchange to the A4 in Slough, the A40/M40 at the Denham Roundabout, the M25 in Maple Cross, the A404 in Rickmansworth town centre, the A411 on a partially grade separated dual carriageway in Watford town centre, and the A41 in North Watford.
The A3220 is a primary A road in London, England. It runs north from Clapham Common to the A40 Westway at Ladbroke Grove.
The A4232, which is also known either as the Peripheral Distributor Road (PDR) (Welsh: Ffordd Ddosbarthu Ymylol) or the Cardiff Link Road (Welsh: Ffordd Gyswllt Caerdydd), is a distributor road in Cardiff, the capital of Wales.
The A345 is a secondary A road in Wiltshire, England running from Salisbury to Marlborough and the A4. The road is a main south–north link across Salisbury Plain, which is renowned for its rich archaeology, and passes many ancient points of interest along its way.
The A899 is a road in West Lothian, Scotland, connecting Broxburn to Livingston.
The Magic Roundabout in High Wycombe, Buckinghamshire, England, is similar to the complex roundabouts in Hemel Hempstead and other places. It is located on the junction of the A40 and A404 roads.
The A40 is a major trunk road connecting London to Fishguard, Wales. The A40 in London starts in the City of London and passes through six London Boroughs: Camden, Westminster, Kensington & Chelsea, Hammersmith & Fulham, Ealing and Hillingdon, to meet the M40 motorway junction 1 at Denham, Buckinghamshire.
Handy Cross roundabout is a major road interchange at Handy Cross, High Wycombe, Buckinghamshire; the junction for High Wycombe, the M40 motorway and the A404 dual-carriageway. It is the terminus of the A4010 which runs to Aylesbury.
This is a list of roundabouts in the state of Massachusetts in the United States. Intersections that are called traffic circles or roundabouts in the rest of the US are referred to as "rotaries" in Massachusetts, as well as other parts of New England including parts of Connecticut, New Hampshire, Maine Rhode Island, & Vermont.