Truck drivers have always appreciated having a great amount of horsepower under the bonnet (or under the cab). It is always good to be able to boast about it to fellow truck drivers, but in fact ample power is a safety feature which facilitates the truck driver's ability to hold the same average speed as car drivers, an important part of overall road safety.
A minimum number of horsepower
While the overall Gross Train Weights of truck combinations had grown after WW II, some trucks still had relatively small and weak engines (it was primarily the Swedish truck manufacturers, and in particular Volvo, that played a major role in the introduction of powerful turbocharged engines).
For this reason, the imposition of a minimum number of horsepower per tonne GTW was discussed in legal circles in a number of European countries.
The Germans pave the way
Germany has always been a leading country when it comes to automobile and truck design, and a major proportion of its transportation is performed by trucks. As a result of this, German legislators decided to introduce a minimum horsepower per tonne train weight in the late 1960s. Since a number of European manufacturers of heavy trucks wanted to sell trucks in Germany, this influenced to a great extent the growth of extra powerful engines, a trend which has been present ever since.
There were two different ways available when designing stronger engines; extremely large (and heavy) naturally aspirated engines with up to ten cylinders and volumes of up to 18 litres, and smaller (12 to 14 litres) efficient and fairly light turbocharged engines. German manufacturers were among those who chose the first alternative, while the second was chosen by the Swedish manufacturers.