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. But unlike trolleybuses or rubber-tired trams; for part of their routes guided buses are able to share roadspace with general traffic along conventional roads, or with conventional buses on standard buslanes.
Guided buses may be articulated, allowing more passengers, but not as many as light rail or trams that do not also freely navigate public roads.
There are only a few examples, but more have been proposed in various countries.
The first guided busway in the United Kingdom was in Birmingham, the Tracline 65, 1,968 feet (600 m) long, experimentally in 1984. It has since been removed. Several guided busways have been planned or built in the United Kingdom.
In Mannheim, Germany, from May 1992 to September 2005 a guided busway shared the tram alignment for a few hundred metres, which allowed buses to avoid a congested stretch of road where there was no space for an extra traffic lane. It was discontinued as the majority of buses fitted with guide wheels were withdrawn for age reasons. There are no plans to convert newer buses.
The kerb-guided bus (KGB) guidance mechanism is a development of the early flangeways, pre-dating railways. The Gloucester and Cheltenham Tramroad of 1809 therefore has a claim to be the earliest guided busway. Earlier flangeways existed, but were not for passenger carrying.
Guided buses are to be distinguished from rubber-tyred systems that cannot run other than along a dedicated trackway, or under fixed overhead power lines.
Optical guidance relies on the principles of image processing. A camera in the front of the vehicle scans the bands of paint on the ground representing the reference path. The signals obtained by the camera are sent to an onboard computer, which combines them with dynamic parameters of the vehicle (speed, yaw rate, wheel angle). The calculator transmits commands to the guidance motor located on the steering column of the vehicle to control its path in line with that of the reference.
Optical guidance is a means of approaching light rail performance with a fast and economical set-up. It enables buses to have precision-docking capabilities as efficient as those of light rail and reduces dwell times, making it possible to drive the vehicle to a precise point on a platform according to an accurate and reliable trajectory. The distance between the door steps and the platform is optimized not to exceed 5 centimetres (2 in). Level boarding is then possible, and there is no need to use a mobile ramp for people with mobility impairments.
The Optiguide system, an optical guidance device developed by Siemens Transportation Systems SAS, has been in revenue service since 2001 in Rouen and Nîmes (only at stations), France, and has been fitted to trolleybuses in Castellon (Spain) since June 2008.
Other experimental systems have non-mechanical guidance, such as sensors or magnets buried in the roadway. In 2004, Stagecoach Group signed a deal with Siemens AG to develop an optical guidance system for use in the UK.
Two bus lines in Eindhoven, Netherlands, are used by Phileas vehicles. Line 401 from Eindhoven station to Eindhoven Airport is 9 km (5.6 mi) long, consists largely of concrete bus lanes and has about 30 Phileas stop platforms. Line 402 from Eindhoven station to Veldhoven branches off from line 401 and adds another 6 km (3.7 mi) of bus lanes and about 13 stops. The regional authority for urban transport in the Eindhoven region (SRE) has decided not to use the magnetic guidance system any more for some years. In 2014 the manufacturer, APTS, was declared bankrupt.
The Douai region in France is developing a public transport network with dedicated infrastructure. The total length of the lines will be 34 km (21 mi). The first stage is a line of 12 km (7.5 mi) from Douai via Guesnain to Lewarde, passing close to Waziers, Sin-le-Noble, Dechy and Lambres-lez-Douai. 39 stop platforms will be provided with an average distance between the stops of 400 m (440 yd). A number of stops will be placed at the right side of each lane. Central stops between both lanes will be placed at locations with limited space at the right side. This requires vehicle to have doors on both sides.
On November 3, 2005, a licence and technology transfer agreement was signed between Advanced Public Transport Systems (APTS) and the Korea Railroad Research Institute (KRRI). KRRI was to develop the Korean version of Phileas vehicle by May 2011.
Since June 2013, 3 miles (1.5 miles each way) of the Emerald Express (EmX) BRT in Eugene, Oregon has used magnetic guidance in revenue service on an especially curvy section of the route that also entails small radius S-curves required for docking. The driver controls braking and acceleration.
On kerb-guided buses (KGB) small guide wheels attached to the bus engage vertical kerbs on either side of the guideway. These guide wheels push the steering mechanism of the bus, keeping it centralised on the track. Away from the guideway, the bus is steered in the normal way. The start of the guideway is funnelled from a wide track to guideway width. This system permits high-speed operation on a narrow guideway and precise positioning at boarding platforms, facilitating access for the elderly and disabled. As guide wheels can be inexpensively attached to, and removed from, almost any standard model of bus, kerb guided busway systems are not tied to particular specialised vehicles or equipment suppliers. Characteristically, operators contracted to run services on kerb-guided busways will purchase or lease the vehicles themselves; as second-hand vehicles (with guide wheels removed) have a ready resale market.
The kerb-guided system maintains a narrow track while still enabling buses to pass one another at speed. Consequently, kerb-guided track can be fitted into former double-track rail alignments without the requirement for additional land-take that might have been necessary were a disused railway to be converted into a public highway. Examples include the Cambridgeshire Guided Busway and Leigh-Salford-Manchester Bus Rapid Transit; in both schemes, it has proved possible to provide space for a wide multi-user path for leisure use alongside the kerb-guided double track. Both the Cambridgeshire and Leigh-Salford-Manchester schemes have reported greatly increased levels of patronage (both on the buses themselves and the adjacent paths), high levels of modal transfer of travellers from private car use, and high levels of passenger satisfaction. 
Tram-like guided busways include:
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