London Buses is trialling satellite technology as a replacement for its £50m real-time tracking system.

The organisation is updating its existing Automatic Vehicle Location (AVL) application and will update it with more accurate, modern technology.

London Buses first introduced AVL 15 years ago and is now looking to newer systems to increase performance as the fleet expands to 10,000 vehicles over the next few years.

The company has started limited trials of global positioning system (GPS) technology in place of microwave-based roadside beacons.

'What we've done is review where the industry is going and with our expansion we are looking at 10,000 buses. The original system was never designed to cope with that number of vehicles,' said Melanie Alexander, business manager in the technical services group at London Buses.

Currently all the capital's buses are fitted with radio systems and a modem on the ticket machine, which communicates with control systems in 80 bus garages and a central control hub in Chingford.

Some 5,000 beacons are attached to lamp-posts across the city. Every 30 to 60 seconds, the bus?s location is calculated using microwave signals from the beacons and odometers on the bus wheels.

Controllers can move vehicles around they become bunched together or services are running late or early, and passengers are told when buses are due, with the Countdown signs.

London Buses wants new systems that will last the next 10 to 15 years, following an increase in buses and services, mainly instigated by Mayor Ken Livingston.

'We are trialling GPS to replace the beacons and thinking about GPRS for data transfer, but we won't make any firm decisions until the summer,' said Alexander.

London Buses is looking at GPS-based systems in Hong Kong and New York, but Alexander says there have been problems with both, which are much smaller operations than London.

'AVL is already the biggest system in the world, and no-one has delivered a GPS system to the scale or time of this,' she said.

The cost of the system will be worked out when London Buses has decided exactly what technology to opt for, likely to be around mid-2004.