This will grow to nine million tonnes by the end of 2011.

They could hold up to 40 people or 45 tonnes of cargo.

These changes increased the weight of the vehicle to 38 tonnes.

This increased to 7000 tonnes per day by 2006, a 6-fold increase from 1970.

The weight of the vehicle went up to 8 tonnes.

Within 40 years, that figure has shot up to almost 80 million tonnes.

The overall weight was also increased to over 18 tonnes.

By 1894, the production rose to 7,000 tonnes per day.

Now it has been restricted from 2001 to 20 000 tonnes.

By 2003, global production had increased to 4.38 million tonnes.