ERP: The advantages

Drivers pay only when using the roads Makes drivers more aware of "true cost" of driving Motorists encouraged to choose whether, when and where to drive May choose a different route, destination, time of travel, or not to travel at all May encourage car pools or use of public transport Smoother ride for those choosing to pay

The boxes come with cards slotted inside them which can be topped up with "credit" at approved outlets, in much the same way as pay-as-you-go mobile phone cards work.

As the car crosses the gantry's laser, the appropriate fee is removed from the total on the card.

At peak times the fee is at its highest - which can be S$3 (�1.20) on particularly busy roads - at others it is free.

Drivers can tell when the system is switched on as illuminated signs on the gantries read "ERP in operation".

The ERP certainly discourages drivers from entering the city at peak times, however, the Singaporean Government - acutely aware of the size constraints of the small island - employs several other methods to cut down on jams.

These include restricting the number of cars that can be bought.

Residents must apply for a Certificate of Entitlement (COE), often costing many thousands of dollars, before they can even be permitted to buy a car.

CEOs are carefully restricted in number and can only be sold on with permission.

Greater jams

Public vehicles - such as taxis and buses - are further restricted in their speed, with alarms fitted to all vehicles which sound continuously if the driver exceeds 80km/h (50mph), even on expressways (motorways).

This is partly designed to reduce accidents caused by speeding drivers, but also to maintain a constant pace to reduce congestion caused by stop-start driving.

The ERP works well on some routes but on others, motorists simply queue up at the approach to the gantries waiting for the switch-off time.

Sometimes this can lead to gridlocks for up to 15 minutes before the evening switch-off time of 1900, creating greater jams than the system is designed to avoid.

If Britain is to adopt a route pricing scheme, the lessons learned in Singapore indicate that it may not be a solution in isolation.

But it could be more successful as part of a more comprehensive public transport set-up, perhaps even with greater controls on car buying.