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Agantry (also known as asign holder,road sign holder,sign structure orroad sign structure) is atraffic sign assembly in which signs are mounted orrailway signals are supported on an overhead support. They also often contain the apparatus fortraffic monitoring systems andcameras, oropen road tolling systems.
Gantries are usually built on high-traffic roads or routes with several lanes, where signs posted on the side of the highway would be hard for drivers to see. Gantries may becantilevered or one-sided on the left, right and center (sometimes referred to as ahalf-gantry orbutterfly gantry), or they may be bridges with poles on each side. Similar gantries are used inrailway signalling or to suspendoverhead lines onmulti-tracklines.
Gantries are commonly used on urban highways in Canada to support overhead signs, with half-gantries used to place signs near exits where space does not permit having signs to the right side of the roadway. Gantries may also be used to hold cameras for toll road entrances/exits and to hold electronic information signs.
Across Canada, highway signage on gantries is generally green, with blue being used for various specific purposes. For example, on Ontario's400 series highways, blue signs are used to indicate outercollector lanes, while the standard green signs are used for inner express lanes. Blue signs are also used to indicate Express Toll Routes (such asOntario Highway 407). Overhead blue signs are also used to indicate roads going into airports.
The style of gantry used are mostly truss gantries. Older gantries have truss supports (round or box) and newer ones are now supported by cylindrical legs. In most jurisdictions in Canada, signs that are mounted on overhead gantries are installed perpendicular to the roadway. In Québec, however, signs are angled slightly face-down towards the roadway such that the sign face is directed towards the motorists below. InNew Brunswick, the opposite is true: signs are angled slightly face-up to capture and reflect more sunlight towards the roadway.
Hong Kong's highways use agantry crane type to support signs. The road signs are usually located on top and some have lights to indicate open or closed lanes.
Gantry signs are being installed at various locations around the trunkmotorway network as increasing amounts of traffic mean thatroad signs at the side of the carriageway are frequently obscured bylarge goods vehicles. They may also consist ofvariable-message signs, and more recentlyActive Traffic Management, to close lanes due to accidents and for other reasons. They can also be used to specify temporary speed limits. Gantries in theUnited Kingdom display exit (junction) numbers, distances to junctions / exits (1 mile, 1/2 mile, 1/4 mile, 1/3 mile, 3/4 mile, 2/3 mile) and destinations reached, and if necessary what lane to use for them.
Gantry signs are used frequently in the U.S., particularly in urban areas wherefreeways have an exit every mile to fit in with the grid system. These half-gantries usually have the exit number and the road or street that can be reached. Gantries can also span the whole road, such as atmajor junctions.
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On railways, gantries span multiplerailway tracks and carry eitherrailway signals,overhead lines or both. A signal gantry is also used where to improve the visibility of multiple signals, for example around a sharp curve.[1]
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