The Tate's Cairn Tunnel on Sunday became the latest to join the city's new HKeToll system, with traffic running generally smoothly in the hours after it was switched on.

The toll booths and Autotoll lanes are now out of action and motorists can drive straight through without having to stop to pay fees. The charges will either be deducted automatically or drivers will be sent a bill.

The system has already been rolled out at several other tunnels in the territory, and next month will see its implementation at the Aberdeen Tunnel.

The government says more than 810,000 electronic tags have so far been issued for motorists to use HKeToll.