[as of 2011]

France has a long-standing tradition of flirting with technologies based on a concept of rubber tired vehicles being guided by a single track in a tram-like fashion. The pictured monorail steam tramway operated between the towns of Raincy and Montfermeil in the eastern suburbs of Paris between 1868-1870.

Nowadays there are two different technologies associated with rubber tired vehicles being guided by a single track. Both have either developmental or implementational roots in France. One was developed by the French company called Lohr, and is known by the name of the public transport subdivision of the above company, called Translohr. The other was developed by the Canadian company Bombardier, and is known as the Guided Light Transit (GLT) or Transport sur Voie Reservee (TVR) in French . The main difference is that the Translohr system assumes that a vehicle remains "attached" to the guiding rail at all times, while the GLT system assumes an option for a vehicle to detach from the guiding rail and run independently while being steered as a regular bus.

Translohr Technology

The weight of the vehicle is borne by rubber tires, while the vehicle is guided by way of two steel single-flanged guide wheels set at 45 degrees to the road surface and at 90 degrees to one other, converging on upper outer rims of the single guiding rail. This provides for a better traction, but precludes the vehicle from detaching / reattaching to the guiding rail.

Translohr guide wheels

Translohr vehicles do not have a steering wheel. There is higher tendency to associate Translohr vehicles with trams, as they are to follow the guiding rail at all times. These vehicles are usually assigned public transport fleet numbers only, but do not bear licenses plates.

The Translohr system is being implemented in Clermont-Ferrand (Fracne), which pioneered it, followed by Tianjin (China) and Padua (Italy). The Translohr system is currently under construction in Mestre, Italy, near Venice.

Guided Light Transit (GLT) Technology

The weight of the vehicle is borne by rubber tires, while the vehicle is guided by way of one steel double-flanged guide wheel set at 90 degrees to the road surface, resting upon the single guiding rail. This provides for less traction, but does provide an option for the vehicle to detach / reattach to the guiding rail.

GLT guide wheel

While the vehicle can detach from the guiding rail at any given point, reattaching to it requires a designated port. GLT vehicles are equipped with a steering wheel, which is used in unguided mode only. There is higher tendency to associate GLT vehicles with trolleybuses, as they do not have to follow the guiding rail at all times, and could be steered independently in mixed traffic. GLT vehicles are usually equipped with license plates like all buses do.

The GLT system was being implemented in Nancy (France), which pioneered it, followed by Caen (France).

The system in Nancy had suffered from various technological problems including a rush of derailments due to poor traction in curves. Overall, while an option to operate the same vehicle in various modes might seem very appealing, the technology associated with such a provision spells a high rate of failures. The system was closed for a year in 2001-2002 for a patchwork to be completed. Upon the system being reopened, speeds in curves were limited to 10 km/h. Consequently, the GLT system is generally considered a failure and is currently not planned for any other cities. Moreover, Bombardier stopped production of GLT vehicles in 2006.

Translohr and GLT Advantages and Disadvantages

Advantages over traditional rail systems:

- Ability to overtake steep grades up to 13%.
- Quieter ride in curves.
- Depot does not have to be located within the immediate vicinity of lines. [GLT only]
- Does not require continuous rail / power supply infrastructure. [GLT only]
- Option to detach / reattach to the guiding rail. [GLT only]

Claimed advantages over traditional rail systems, reverted upon actual operations:

- Smooth ride.
- Requires less infrastructure.
- Cheaper investment.
- Ability to overtake tighter curves.

Advantages over traditional rubber tired vehicles:

- Longer vehicles with high passenger carrying capacity. [Translohr only]
- Psychological perception of a fixed line based on a presence of a physical rail attracts significantly more riders.
- Additional road safety due to predictable movements.
- Aligned docking at low-floor platforms.
- No need for additional loading equipment for wheelchairs.
- Narrow right-of-way due to precise drivability.

General disadvantages:

- High rate of derailments.
- Expensive rolling stock.
- Complicated technology, and jam-packed design.
- High technology failure rate.
- Complicated / expensive rolling stock maintenance.
- A need for extra rolling stock due to high rate of technical failures and complicated maintenance.
- Excessive / expensive infrastructure installation.
- High wear and tear of road surfaces from rubber tires continuously following the same path.
- High wear and tear of road surfaces due to excessive weight of vehicles.
- Excessive / expensive maintenance and frequent replacements of road surfaces within the right-of-way.
- Frequent replacements of rubber tires due to excessive wear and tear.
- A need for frequent infrastructure monitoring.
- Not practical in regions prone to snow.
- Sensitive to debris on track.
- Proprietary issues due to dealing with single technology provider / high costs due to absence of competition in procurement.
- Serious danger to bicycles and motorcycles due to large gaps surrounding the guiding rail. [Translohr only]
- Excessive noise produced by guiding wheels. [Translohr only]

Additional disadvantages if compared to traditional rail systems:

- Poor quality of ride.
- Excessive friction resistance for rubber tires and added power consumption.
- Excessive centrifugal force in curves, prompting slow speed in curves. [Especially true for GLT]
- Limited vehicle length. [GLT only]
- Fragility of guiding wheels.
- Complicated derailment management.

Additional disadvantages if compared to traditional rubber tired vehicles:

- Vehicles are confined to the guiding rail. [Translohr only]
- Reattachment to guiding rail at designated ports only. [GLT only]
- Poor steering / low controllability of movement in unguided mode. [GLT only]