Traffic Sign Design/Overview
At the most basic level a traffic sign can be in the form of a vertical sign, a road marking or an electronic device.
- 1 Vertical Signs
- 1.1 Picture Signs
- 1.2 Worded Signs
- 1.3 Types of Signs
- 1.4 Further Reading
- 2 Road Markings
- 3 Electronic Devices
Vertical signs are used to communicate information to all users of the public highway. They can be split into three basic forms: warnings, regulations and information. These traditionally have been triangular, circular (round) and rectangular (oblong) but, as always, life is never as simple as that.
The modern use of pictures for informing all users of the public highway evolved from an agreement at the Vienna Convention on Road Traffic that standardised on international traffic laws in 1968. The Signs and Signals element expanded on the Geneva Protocol on Road Signs and Signals in 1949, and formed the basis for the current set of symbols approved for use on the public highway by the Department for Transport.
The DfT allow the use of a prescribed set of symbols on vertical traffic signs, these symbols fall into one of three categories:
- General Symbol Drawings (S Series)
- Tourist Symbol Drawings (T Series)
- Approved Tourist Symbol Drawings (AT Series)
The first two categories are in general use and form the basis for the signs we actually see. These pictorial signs are split into five categories by the DfT:
Warning signs (P500 series)
Signs warning of hazards to road users.
Regulatory signs (P600 series)
Signs warning of restrictions or instructions to road users.
Railway and tramway level crossings (P700 series)
Signs warning of trains or trams crossing the road ahead.
Miscellaneous informatory signs (P800 series)
Various signs not covered by any of the above series.
Bus, tram and pedal cycle facilities (P900 series)
Signs for public transport and pedal cyclists, as well as information about these facilities for other road users.
Because of the complex nature of the messages that need to be communicated to drivers and other road users, it is not always possible to use just symbols, so many of the above categories include worded elements to either clarify or embellish the message being communicated by the picture signs.
Worded signs generally started out as a means of directing motorists to destinations, but the sometimes complex messages that need to be communicated often require some form of wording to clarify or embellish the meaning of the picture sign.
All worded vertical signs on the public highway use a set of standard typesets (fonts), these being:
- Transport Medium – Light letters on dark backgrounds
- Transport Heavy – Dark letters on light backgrounds
- Motorway White – For route numbers on blue backgrounds
- Motorway Black – For route numbers on yellow backgrounds
The proportions of these typesets or "alphabets" as the DfT calls them, are the same for all sizes of typeset used. The size of typeset is referred to as the "x-height", which refers to the height of the lower case X in the alphabet, with each character set onto what is referred to as a "tile", which is twice the size of the x-height. The width of the tile defines the spacing between characters, and thus the overall size of the worded sign.
Another unit of measurement called the "stroke width" is used to design the spacing of worded signs. A stoke width is not a fixed size, but a proportion of the x-height: there are 4 stroke widths (sw) to the x-height and each tile is 8sw high. The characters are set 2sw up from the bottom edge of the tile and upper case characters extend to a height of 5.6sw.
Using the fixed proportion fonts allows sign designers to design a sign, then adjust the size of the sign to suit visibility requirements without compromising the overall proportional look of the sign. The symbols used in all sign designs are also in stroke widths and scale according the chosen x-height.
Worded signs are defined by the DfT into the following categories:
- Warning signs (P500 series)
- Regulatory signs (P600 series)
- Railway and tramway level crossings (P700 series)
- Miscellaneous informatory signs (P800 series)
- Bus, tram and pedal cycle facilities (P900 series)
- Directional signs (P2000 series)
- Signs for road works (P7000 series)
Types of Signs
Beyond the technical terminology, a whole host of phrases has evolved either through official processes or through popular culture.
- Driver Location Signs – Signs to identify a location in case of emergency
- Route Confirmation Signs – Signs that confirm the route and destinations
- Butterfly Sign – Diverge of two major roads
- Chopsticks – Sign indicating the start of motorway restrictions
- Flag Sign – Pointy ended signs
- Fork Sign – Signs found in advance of Grade Separated Junctions
- Gantry Sign – Overhead sign on busy roads
- NO Sign – Original Chopsticks
- Snow Warning Signs – Signs to indicate when roads are closed due to bad weather
- Traffic Sign Design - Materials – Materials used in sign faces
- Pre Worboys – Information on signs installed before 1964
- Primary Destinations – Primary Destinations are key destinations on direction signs
- Regional Destinations – Super Destinations shown on direction signs
- Worboys Report – Review of British traffic signs in 1962–63
Road markings can be formed using thermoplastic, cold plastic, preformed material or paint, and may be laid as permanent markings or as temporary markings at road works. The DfT categorise all road markings under:
- Road markings (P1000 series)
Applied Road Markings
In general, the use of thermoplastic applied screed is the most popular form of road marking material. Complex shapes such as pedestrian/cycle symbols are available as preformed shapes that are applied to the carriageway, but typically the thermoplastic material is applied to the road using either a screed dragbox or a screed pram.
Road markings communicate messages about hazards and regulations that apply to the public highway: white is generally used for most general road markings, with yellow reserved for communicating regulations on waiting, loading and stopping. Road markings can be applied on the actual road carriageway, applied to the kerb or used on the footway but, in general, each type of road marking will have a specific location of use.
Road studs are used to supplement longitudinal road markings. Traditionally they relied on reflecting light back from the headlights of an approaching vehicle using either glass reflectors or by using high intensity retroreflective material. Recent developments in solar power have seen the introduction of LED road studs, which charge a battery through the daytime that then powers the LEDs through the dark periods.
Typically, road studs are deployed where traffic flows are high, or there is no street lighting, or where there the road is susceptible to fog. Road studs are always provided on motorways and regulations require that road studs are used in double white lining systems.
Four colours are prescribed for use by the DfT:
- White – to indicate traffic lanes
- Red – to indicate a line of studs that shouldn't be crossed or the left hand side of the running carriageway
- Amber – to indicate a line of studs that shouldn't be crossed or the right hand side of the running carriageway
- Green – to indicate a line of studs that may be crossed
(Definitions of use are more comprehensive and outlined in the Traffic Signs Manual.)
Numerous devices exist to give variable information to motorists and other road users: these include traffic signals, lane control devices and variable message signs (VMS) and car park guidance signs (CPGS).
Traffic signals provide guidance to all road users on the suitability to proceed. Road based users are presented with a combination of red, amber and red illuminated signals, with a series of prescribed options for dedicated movements. Non motorised users are presented with just red and green illuminated signals to indicate the suitability of crossing the road. These can include symbols for pedestrians, cyclists and equestrians.
A less common prescribed configuration of illuminated signals provides a facility to signal control access for less well used facilities such as level crossings, moving bridges, tunnels, airfields and premises for emergency services. These are often referred to as "Wig-wags". A pair of flashing amber lights is a further configuration, that is generally used to indicate regular short periods of activity, such as school crossing patrols or children accessing a school.
Although uncommon on the public highway there are illuminated signals for trams, which are illuminated in white as: a near-vertical bar to indicate the tram may proceed (the equivalent of a green traffic light), a solid dot to indicate the tram must stop if possible (the equivalent of an amber light), or a horizontal bar to indicate that the tram must stop (the equivalent of a red light).
Categories as defined by the DfT:
- Traffic signals (P3000 series)
- Signals for crossing facilities (P4000 series)
Lane Control Signs
Where the use of lanes can be varied, typically through tunnels for routine maintenance, to provide for tidal differences at toll booths or to provide a tidal flow lane, a set of symbols are prescribed for use by the DfT. These signals indicate with an illuminated green arrow (facing down) that a lane is open for use, or an illuminated red cross to indicate a lane is closed. A less used symbol, an illuminated white arrow pointing down and to the left is used to indicate that traffic must move to the left hand lane as soon as it is safe to do so.
Category as defined by the DfT:
- Lane control signs (P5000 series)
Variable Message Signs
The use of static signs does provide a suitable means of communicating information to motorists, however some signs are required to communicate variable information to motorists. These have taken the basic form of a flap type sign, slightly more advanced rotating prism type signs and the most advanced matrix type signs.
The most basic of flap type signs are generally used as triggers to diversion routes when key roads are closed due to incidents, with the message being changed by a police officer, traffic officer or maintenance operative. Prism type signs are generally more expensive and are typically used for locations that require regular display of a variable message (side winds, moving bridge or tunnel closures) or where the signs are difficult to access on foot (on high speed roads, on bridges or in tunnels).
Matrix signs are now mostly illuminated units, whilst the original matrix signs displayed messages using coloured disks that flipped from black to luminescent yellow. There are numerous different applications of matrix type signs prescribed for use:
- Central Reserve Post Mounted Signals
- Slip Road Mounted Signals
- Gantry Mounted Signs
- Enhanced Message Signs – typically two lines of text
- Message Sign Mark 3 (MS3)
- Message Sign Mark 4 (MS4)
Another more recent development is for managed/controlled motorways, where variable message signs used to display more detailed information on incidents, lane closures and speed limits.
More information on VMS is available on the Highways Agency Website
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