Guided Light Transit (GLT, french: Transport sur Voie Réservée or TVR) was the name of

guided bus Guided buses are buses capable of being steered by external means, usually on a dedicated track or roll way that excludes other traffic, permitting the maintenance of schedules even during rush hours. Unlike trolleybuses or rubber-tired tra ...

technology and associated infrastructure designed and manufactured by

Bombardier Transportation Bombardier Transportation was a Canadian-German rolling stock and rail transport manufacturer, headquartered in Berlin, Germany. It was one of the world's largest companies in the rail vehicle and equipment manufacturing and servicing industry ...

(now

Alstom Alstom SA is a French multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the AGV, TGV, Eurostar, Avelia ...

). It was installed in two French cities: Nancy and

Caen Caen (, ; nrf, Kaem) is a commune in northwestern France. It is the prefecture of the department of Calvados. The city proper has 105,512 inhabitants (), while its functional urban area has 470,000,Nancy system is in operation, however it will be withdrawn in February 2023 and replaced by trolleybuses. The Caen system has been abandoned and now rebuilt as a conventional

tram A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport are ...

way by 2019. Both of the systems in these cities are referred to as " tramways on tyres", and in common with

systems they use a surface guidance system and in normal operation are powered by electricity drawn from an

overhead wire An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipmen ...

. However, while the vehicles are guided by a central guidance rail, they ride on rubber tyres, not on

rails Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail transport) or railway lines, the running surface of a railway Arts and media Film * ''Rails'' (film), a 1929 Italian film by Mario Camerini * ''Rail'' ( ...

. There has been disagreement about whether they should be called "trams", for that reason and also because they are capable of being steered and operating independently of the guidance rail, using auxiliary diesel engines. GLT is effectively a model of guided

dual-mode bus A dual-mode bus is a bus that can run independently on power from two different sources, typically electricity from overhead lines like a trolleybus or from batteries like a hybrid bus, alternated with conventional fossil fuel (generally diesel ...

, but when GLT vehicles use a

pantograph A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...

to collect current, as do those in Caen, they are not commonly considered to be

trolleybus A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tramin the 1910s and 1920sJoyce, J.; King, J. S.; and Newman, A. G. (1986). ''British Trolleybus Systems'', pp. 9, 12. London: Ian Allan Publishing. .or troll ...

es. English transport publications generally refer to the GLT and the competing Translohr system as "

rubber-tyred tramway A rubber-tyred tram (also known as tramway on tyres, french: tramway sur pneumatiques) is a development of the guided bus in which a vehicle is guided by a fixed rail in the road surface and draws current from overhead electric wires (either ...

s", but rarely simply as "tramways", as they are not tramways in the conventional sense, but neither are they buses when pantograph-equipped and operating in service as designed (''i.e.'' in electric mode). GLT was one of the few models (together with the

Innovia APM Innovia APM is a rubber-tired automated people mover system (APM) currently manufactured and marketed by Alstom as part of its Alstom Innovia, Innovia series of fully automated transportation systems. The technology was introduced in 1963 by West ...

) of rubber-tyred vehicles produced by Bombardier's transport division, which is otherwise focused on

rail transport Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a p ...

Characteristics

GLT and the similar Translohr are often described as the tram equivalent of

rubber-tyred metro A rubber-tyred metro or rubber-tired metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tires that run on rolling pads inside guide bars for traction, as well as traditional ...

technology, but this is not strictly accurate; while the GLT follows a central rail, the rail does not support the vehicle, and the actual wheels which are as independent as those of a regular

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...

. The wheels of rubber-tyred metros, on the other hand, are bound and guided by their rails in the same way as are steel-wheeled trains. Unlike trams and Translohr vehicles, GLT vehicles have a

steering wheel A steering wheel (also called a driving wheel (UK), a hand wheel, or simply wheel) is a type of steering control in vehicles. Steering wheels are used in most modern land vehicles, including all mass-production automobiles, buses, light and ...

, though it is not used when following a guidance rail. On the GLT line in Nancy, more than one-third of the 10-km route has no

guide rail A guide rail is a device or mechanism to direct products, vehicles or other objects through a channel, conveyor, roadway or rail system. Several types of guide rails exist and may be associated with: * Factory or production line conveyors * Pow ...

, and steering is controlled entirely by the driver on those sections. The Nancy GLT system is operated by the ''Société de Transports de l'Agglomération Nancienne'', or ''STAN''. With two articulation points and a total length of , GLT vehicles are shorter than most modern trams, but long compared with conventional buses. They are designed to look like trams, but they are unidirectional and have bus-like

rear-view mirror A rear-view mirror (or rearview mirror) is a flat mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's rear window (rear windshield). In cars, the rear-view mirror is usually affixed to ...

s. They have 100%

low floor Accessibility is the design of products, devices, services, vehicles, or environments so as to be usable by people with disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i. ...

s, have 40 seats, and have standing room for as many as 105 passengers. In Caen, where the central guidance rail has been installed on all sections of the passenger-service route, the vehicles collect their power from a

, returning it through the central guidance rail, and use their

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

s and steering wheels only while travelling to and from the depot. Use of a pantograph effectively requires that a surface guidance system be used, to ensure the vehicle remains approximately centred below the

, so that its pantograph does not slip out from underneath the wire. The Caen vehicles thus cannot move laterally away from the overhead wire except when running in diesel mode (as conventional buses), and for this reason the Caen route is not commonly considered to be a

system. Nancy's fleet of 25 GLT vehicles use dual

trolley pole A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" (electrified) overhead wire to the control and the electric traction motors of a tram or trolley bus. It is a type of current collector. Th ...

s to collect and return their electric power, in order to allow the use of existing wires constructed for use by the town's previous generation of trolleybuses and to permit operation, where desired by the transport authority, away from the guide rail. The Nancy vehicles follow a guidance rail on about 60% of the route, and thus the Nancy route uniquely is considered to be both a rubber-tyred tramway and a trolleybus line. The system was first brought into use for passenger service in February 2001, but operation was suspended from March 2001 through March 2002 while Bombardier performed upgrades to the vehicles. In Caen, the GLT fleet began operation in November 2002, incorporating the changes made to Nancy's vehicles during the upgrade. They were operated by the ''Compagnie des Transports de l'Agglomération Caennaise'' under the name ''Twisto'' until 2017, when the system was shut down and replaced by a conventional

tram system A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport are ...

Advantages

While the GLT's central guidance

rail Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail transport) or railway lines, the running surface of a railway Arts and media Film * ''Rails'' (film), a 1929 Italian film by Mario Camerini * ''Rail'' ( ...

is not significantly less expensive than the rails needed by regular trams, the overall system can be installed at a lower cost since existing trolleybus wires can be used without the installation of tracks, and not all new sections need have either rails or electric wires installed; even if the entire passenger route is equipped with guidance rails and wires, as in Caen, the depot need not be located immediately by the track, saving planners from having to find space for a new yard in what may be a central and high-valued area of the city. Another advantage over trams, which was particularly of interest to planners in Nancy, is that rubber tyres give significantly more traction than steel wheels, and so can be used to climb steeper hills, up to a

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

of 13%. The Nancy route T1 includes a section with a 13% grade. Compared to buses, the use of a guidance rail allows GLT vehicles running in parallel lanes to pass closer together than drivers could safely steer. They can also draw up to level, tram-like platforms that allow for easier boarding, and give access to passengers dependent on

wheelchair A wheelchair is a chair with wheels, used when walking is difficult or impossible due to illness, injury, problems related to old age, or disability. These can include spinal cord injuries ( paraplegia, hemiplegia, and quadriplegia), cerebr ...

s without requiring the time-consuming deployment of ramps or 'kneeling' systems.

Disadvantages

The GLT systems in place have experienced some mechanical problems which, though they have largely been resolved, have discouraged some other cities from adopting the technology. The vehicles have shown a tendency to move erratically when running free, and do not respond well should the driver mistakenly attempt to steer while following the guidance rail (for example, to avoid a pedestrian or animal running into the street). In addition, due to the tyres running over the same spot in the road, in both Nancy and Caen there has been significant rutting of the roadway, resulting in extensive repairs at significant cost to the operator. This could be considered to add to the already high running costs. Ride quality is also said to be poor, not much of an improvement on a bus, due to the four-wheeled design, whereas trams have

bogie A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...

s. Guidewheel mechanical failures have occurred, causing the trolleybus to swerve off the roadway. This is due to the high

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

s exerted on the wheel when rounding corners. Due to this, a speed limit of 10 km/h is now enforced on corners. One of the main aims of the system, to achieve a lower cost per kilometre than trams, has failed. Other French tramways achieve a cost per kilometre at least 10% lower than that for the guided bus. Similarly, the cost per person of the vehicles is also noticeably higher with the guided bus than a tram. Where

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

fall is an issue, this system may not be practical: since the guide rail forms the return leg of the electrical circuit, accumulation of ice and snow on the rail could cause intermittent power interruptions to the vehicle. Also, as the vehicle does not place a significant portion of its weight on the guide wheel (most of it being supported by the rubber tyres), snow packed into the flangeways or atop the rail by road traffic could lift the guide wheel off the rail, leading the vehicle to go off course. Critics of the system also point out that, unlike a conventional tramway, GLT is a

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