Astrophysicist

Stellar motion, as observed from Earth, comprises two components: radial and transverse velocity.  And so with traffic: look at it directly in the dark and it's hard to tell if it's coming or going.  (You generally haven't time to measure the Döppler shift of its lights, or the wavelengths from a car horn).

So, don't be dazzled by looking directly at the metal-&-silica lump rocketing toward you: observe respective motion between its limb and "the ISM", or background noise.  Glance sideways to use the parallax between your window sill and the "celestial canopy" of the tarmac beyond: that will show you the speed of your own motion as observer, to gauge any closing speed with respect to another car.

Click the image to come back to “Life”

It may not be on the scale of Keplerian mechanics, but any physical contact WILL result in conservation of momentum in just the same way if your car makes Close Encounters of the Third Kind ... dissipating energy via frictional heat and big/scary sounds.  And we'd rather that stayed in the stellar photosphere, no?