British supermarket giant Asda, a subsidiary of US behemoth Wal-Mart, is to invest £2.4m (US$3.6m) is rolling out 'Techno-trollies', a new system which dramatically reduces the number of trolleys taken from stores.

The rollout comes after a hugely successful trial at six stores in England, Wales and Scotland. Prior to the trial, Asda stores lost almost four in five of its trolleys each year. But the 'Carttronics' system has slashed this to less than one in 20.

Now Techno-trolleys will be rapidly rolled out to another 37 locations, ensuring that the stores responsible for seven in ten of all trolleys lost each year are covered by the end of 2002. The first, Irvine in Scotland, is being installed this week.

Techno-trolleys technology involves using radio waves to mark the boundary around the store where trolleys can freely circulate. When a trolley passes through this invisible boundary, a signal is sent to a receiver on the trolley which tells it to lower a brake onto the wheels bringing it to a controlled stop.

New trolleys cost up to £100 each, and the new scheme will minimise the cost of replacing those lost from each store's fleet, ensuring they're always available to customers and cutting the risk to the local environment from abandoned trolleys.

"Our new system will put an end to trolley traumas, keeping them available to shoppers at the store," said Chris Woodcock, Asda's trolley contracts manager.