The speed of light is 300,000 km/s, or about 671,000,000 miles per hour. Quite a few orders of magnitude larger than 90 mph.

The kinetic energy of an object depends on both its mass and its velocity. A fly against your car is light enough, and the velocity of your car is small enough, that a collision between a car and a fly does nothing to the car. Once you approach lightspeed though, even a speck of dust could wreak havoc