don't forget wind. Can have a huge effect on it. if you have a strong wind coming across the vehicle that is pass, towards your vehicle, it will be a lot more violent, than if the wind was going the opposite direction
Semi's punch such a large hole in the air, right around the cab doors usually there is a low pressure zone thats big enough to move you towards the truck, then at the bumper, you hit the high pressure zone and it pushes you out. When wind conditions are right, the low pressure zone can be really powerful and will scare teh crap out of you if you're on a bike