The many accidents involving lorry-mounted cranes clearly show that it is extremely risky to depend on the driver to remember to lower the crane before driving off ("Lorry driver held over collapse of walkway shelter"; June 18).

I previously wrote in to suggest that the authorities implement a compulsory interlock system on such vehicles to prevent them from being driven off when the crane has not yet been lowered ("Do more to stop tall vehicles hitting overhead structures"; Nov 15, 2012).

The Land Transport Authority said that it would do a feasibility study on my suggestion ("LTA to keep educating drivers of tall vehicles on safety aspects"; Nov 22, 2012). I have heard nothing about the matter since then.

The LTA was testing a height detection system ("LTA to test alert system for drivers of tall vehicles"; Nov 6, 2012). However, it will be extremely costly to "protect" every overhead pedestrian bridge, flyover and other such structures in Singapore.

Besides the question of reliability in all weather and lighting conditions, the driver may not know that the height warning is for him and may not be able to stop the vehicle in time.

There is also no guarantee that there will not be any damage to vehicles or injuries to people should a collision occur.

An interlock system will be much better and more cost-effective, because it stops the hazard at the source.

Ong Hong Bee