The definition of a terrorist in our dictionary is "A person who uses or favours violent and intimidating methods of coercing a society".

Since most of society uses the roads, we believe that someone who uses violence and intimidating methods to coerce the driving public into giving way etc can fairly come into the definition of "terrorist".

And if some jerk who chases you up the motorway at 140kph or deliberately uses his vehicle to try to knock you off your bike doesn't qualify as a terrorist, no-one does.