SINGAPORE - To reduce the risk of crane lorries colliding into overhead road structures, these vehicles will have to be fitted with audio warning systems from next year (2017).

These systems will detect if the lorries' cranes have been stowed, and alert the drivers through an audio buzzer in their cabins.

Since 2013, there have been 20 cases of overhead road structures - such as walkway shelters and overhead bridges - being hit by vehicles which are over the height limit.

In June this year, a crane lorry crashed into a walkway shelter at an open-air carpark in Bukit Batok, causing the structure to topple and crush a car.

"Many of these incidents could have been prevented if the drivers had stowed the cranes before setting off," the Land Transport Authority (LTA) said in a press release on Wednesday (Nov 30).

Under the new regulations, all lorries mounted with cranes after Jan 1, 2017 are required to have the audio warning systems.

All existing lorries with cranes have until Sept 30, 2017 to comply with this requirement, the LTA added.

For cranes which can be fully stowed, a limit switch is to be installed at the base of the crane, and linked to an audio buzzer in the driver's cabin.

When the crane boom is fully stowed, it will rest on a mechanical lever of the limit switch. When it is not, the lever is lifted and this triggers an audio warning to the driver.

For crane booms which cannot be fully stowed, an angle sensor can be installed on the inner boom, instead of a limit switch. This sensor will alert drivers when the crane is not fully stowed and is above its maximum stowed height.