Final answer:
In your situation, the car moving in the opposite direction would appear to be moving faster due to relative velocity, which is the combination of your speed and the other vehicle's speed as observed from your reference frame.
Step-by-step explanation:
When you are riding in a car and observing two other cars passing by, one moving in the same direction as you and the other in the opposite direction, the car moving in the opposite direction will appear to be moving faster. This is due to the concept of relative velocity. Relative velocity is the velocity of an object as observed from a particular reference frame, and it can be calculated by vector addition of the velocities involved. From your perspective in the car, you are adding the velocity at which you're moving to the velocity of the car coming towards you. This sum is greater than the velocity of the car moving in the same direction as you, making the oncoming car appear faster.
For example, imagine you're moving at 30 mph and the car going the same direction passes you at 40 mph, while the car coming towards you also passes at 40 mph. In this case, the car going the same direction is traveling at a relative speed of 10 mph (40-30), while the car coming towards you appears to be moving at 70 mph (40+30) relative to you.