WHy

is it that when im in a car traveling at some speed and i observe another car traveling at my speed plus some arbitrary amount (lets say +5mph) i observe that cars motion at less than the actual difference in speed between my car and it.

tl;dr

why do cars going alot faster than me on the highway look like they are going maybe 3-4mph past my window

>>4
NO

when a car passes me going 10mph faster, it appears to be going 4-5mph past me

it should appear that they are going the full 10mph faster. It should be no different than if i was at a stand still and a car was driving 10mph past me, but this isnt the case. In both cases, at the end of the hour, the other car is 10miles in front of me, why does it appear different when im traveling faster?