The reason a car appears to be approaching you at a speed higher than its actual speed is due to the Doppler effect. The Doppler effect is a phenomenon observed with waves, including sound waves and electromagnetic waves, such as light. It occurs when there is relative motion between a wave source and an observer.
When a car is moving toward you, the sound waves it generates are compressed in front of it, causing the sound waves to have a higher frequency. This increase in frequency makes the pitch of the sound higher than what you would hear if the car were stationary. As a result, the car's engine and other noises seem higher-pitched, and this is often described as the car "sounding" faster.
Similarly, the Doppler effect affects light waves, although in most everyday situations, the effect is negligible for visible light because the speeds involved are much smaller than the speed of light. However, for objects moving at very high speeds (close to the speed of light), such as stars or galaxies, astronomers must consider the Doppler effect when interpreting their observed spectra.
In summary, the apparent increase in speed when a car approaches you is an illusion caused by the compression of sound waves due to the relative motion between the car and the observer.