Star.pngStar grey.pngStar grey.pngStar grey.pngStar grey.png

Single carriageway

From Roader's Digest: The SABRE Wiki
Jump to navigation Jump to search
Single Carriageway
Overhead Gantry - Geograph - 1222184.jpg
Birmingham's A38(M) is an example of a multi-lane single carriageway road
Cameraicon.png Pictures related to Single carriageway
No pictures uploaded (Upload?)
Quick Links
Single track road • Dual carriageway


A Single carriageway road is a road where there is a single continuous surface to the road, with no physical barrier separating the directions of travel. It is the most common form of road standard in the United Kingdom and Ireland. The term does not refer to the number of lanes - whilst most single carriageway roads have one lane per direction of traffic (known as S2), two lanes per direction of traffic (known as S4) can be found in many locations. Up until the early 1980s, it was common to find three-lane single carriageway roads (known as S3), where the central lane was designed for use by traffic wishing to overtake slower vehicles but these roads (colloqually known as suicide lanes for obvious reasons) are now very rare - probably the best example is on the A6 near Shap, Westmorland.

The widest single carriageway road in the United Kingdom is the A38(M) Aston Expressway in Birmingham, which is 7 lanes wide and uses Tidal Flow.

Single carriageway roads are generally found on routes with low to medium volumes of traffic.

Single Carriageway Types

These designations can be used in multiple ways and have multiple implications. The basic rules are:

  • If there is an even amount of lanes in both directions (and/or non-priority shared lanes) OR are 1-way streets they are designated as Sx or WSx, x being the total amount of lanes.
  • If one direction has more lanes than the other than the larger number of lanes come first then the smaller number after such as Sx+y or WSx+y, with x being the larger amount of lanes and y being the smaller amount of lanes.
  • If the carriageway is purposefully wide, except for turning lanes then the S is substituted for WS.
  • Personal discretion if bus lanes are included in the amount of lanes.
  • Turning lanes are not included in the number, unless they form from a running lane, or are significantly long.
  • Single Carriageways with a hard shoulder are extremely rare, and normally gets a WS destination.
  • Cycle lanes are discarded from the number of lanes, including contraflow lanes.

S1

B983 near Machrihanish - Geograph - 23107.jpg
Cameraicon.png Pictures related to S1
View gallery (319)

S1 refers to normally a Single Track, it's only wide enough for 1 vehicle in 1 direction. In rural areas with very low traffic these can be two way roads, however on busier routes or urban areas it can make up parts of 1 way streets.

S2

19814352.jpg
Cameraicon.png Pictures related to S2
View gallery (4734)

S2 is a typical road, normally provides both directions of travel with their own dedicated lane, normally overtaking is permitted. Two-lane 1 way streets come under S2

S3

A30 S3 - Coppermine - 15015.jpg
Cameraicon.png Pictures related to S3
View gallery (28)

S3 roads are hard to come-by now, they were common as they allowed overtaking in both directions, even when there was oncoming traffic (as long as oncoming traffic wasn't over taking). Most S3s were converted into WS2 or S2+1. Most S3 nowadays are found on Gyratories or 1-way roads which have three lanes.

S2+1

A96 Near Huntly - Coppermine - 2309.jpg
Cameraicon.png Pictures related to S2+1
View gallery (132)

S2+1 Are S3 roads, however one side of the road has priority or dedication of using the middle lane.

S4

The Hawthorns - Geograph - 13405.jpg
Cameraicon.png Pictures related to S4
View gallery (61)

S4 are single carriageway roads with two lanes of traffic in both directions.

WS2

A303 Ilminster Bypass June 2002.jpg
Cameraicon.png Pictures related to WS2
View gallery (57)

WS2 are roads which have two lanes of traffic, 1 lane in either direction. However are extra wide which have some benefits such as vehicle separation being larger, or if a vehicle or something is partially blocking the carriageway, it may not affect the flow of traffic. However does encourage faster traffic and potentially unsuitable overtaking.

S5,S6,S7

Single carriage roads with more than 4 lanes are most common as brief stretches near junctions. Where they exist, they can be described with an 'S' followed by the total number of lanes. The A38(M) is the widest single carriageway road in Great Britain, and is an S7; a notable S6 is The Mall in London between Trafalgar Square and Buckingham Palace. Another example of an S6 is the A60 Trent Bridge at the boundary of West Bridgford and Nottingham.






Single carriageway
Road Basics
Physical layoutSingle track • Single carriageway • Dual carriageway • High Quality Dual Carriageway • Road Widths • Urban Streets • Abandoned Road
Legal typesAll-purpose Road • Special Road • Motorway • Trunk road • Principal road • Classified Numbered road • Classified Unnumbered Road • Unclassified road • Primary Route • Non Primary Route • Right of Way • Unadopted road
Road numbers1922 Road Lists • Classification • Defunct road • Euroroutes • MoT Maps • National Cycle Network • Numbering principles • Numbering anomalies • Disputed Numbers • Recycled number • Unallocated numbers • Fictional Road Numbers • Junction numbers • Essential Traffic Routes
Road FeaturesArterial Road • Automatic Bollard • Balancing Pond • Belisha Beacon • Bott's Dots • Bypass • Cannon • Cats' Eyes • Cattle Grid • CD Lanes • Central Reservation • Chopsticks • Crash Barrier • Cuttings and Embankments • Cycle Lane • Emergency Phone • Escape lane • Expressway • Fingerpost • Flare • Ford • Gore • Green Bridge • Green Wave • Hairpin bend • Hard shoulder • Island • Junction • Layby • Level Crossing • Local Access Road • Managed Motorways • Milestone • Multi Lane Drop • Multiplex • No-Car Lane • Nose • Oxbow Road • Parapet • Petrol station • Play Street • Raised Pavement Markers • Ramp Metering • Retaining Wall • Road Studs • Roadside Art • Roadside Quarry • Roadworks • Secret motorway • Signage • Smart Motorway • Snow pole • Speed Limit • Spur • Street Lighting • Surface Dressing • Temporary terminus • Throughpass • Tidal Flow • Tiger tail • Toll booth • Traffic cone • Traffic Signals • Tunnel • Vehicle Recovery • Walking and Cycling Friendly Road • Weaving • Wig-Wag Signals • Winter Maintenance • Zip merge
Traffic CalmingBuild-Outs • Chicane • Dragon's Teeth • Home Zone • Low Traffic Neighbourhood • Pinch Point • Quiet Lane • Rumble strips • Safety Cameras • Sleeping Policeman • Speed bump
Public Transport FeaturesBus Lane • Bus stop • Guided Busway • Park and Ride • Tramway • Trolleybus System
Other termsAnderson report • Guildford Rules • Highway Authority • Highway Code • Model Traffic Area • Motorway alphabet • Pre-Worboys • Primary Destinations • Roads by 10 • Transport alphabet • Worboys report
AcronymsAADT • ADS • ANPR • ATM • DfT • GSJ • HA • HATO • HE • HETO • HQDC • LAR • LILO • LTN • MOVA • NCN • NMU • NRA • PBU • POPE • PTS • PFI • RCS • SABRE • SCOOT • SSD • SON • SOX • SRN • TEN-T • TERN • TfL • TII • TOTSO • TRO • TSM • TSRGD • UTC • VAS • VMS • VSL

SABRE - The Society for All British and Irish Road Enthusiasts
Discuss - Digest - Discover - Help