Tyres of a moving truck acquire negative charge by friction from the road. Parts of the metal body of the truck near the tyres then become positively charged by induction and sparks may be produced. This can cause flammable material in the truck to catch fire or explode.
That is why trucks carrying inflammable liquids usually have a metal chain dangling to the ground at the rear. Oil tanks and pipes are earthed to prevent static electricity from building up.
Aircraft tyres are made of slightly conductive rubber so that during touchdown, the charges that have built up on the body of the aircraft during flight can be discharged harmlessly.
