The fastest cars are race cars. F1 and rally cars can go much faster than regular cars. In America they also have races to see what car can reach the fastest speed on a straight stretch of road.
But let's answer that question for the passenger cars that we see driving around town.
The maximum speed of Toyota's passenger cars is 180 km/h.
The maximum speed limit in Japan is 100 km/h. However, some flexibility in speed is necessary so that cars going uphill or carrying heavy loads or many passengers are able to maintain their speed and not hold up traffic. In addition, sometimes it's necessary to go beyond the speed limit to avoid danger. That's why we make cars that are capable of traveling faster than the speed limit.
For example, it's necessary to have some flexibility in speed when cars are going uphill or carrying heavy loads or many passengers so that they can go beyond the speed limit when necessary to avoid danger.
After taking various issues into consideration, it was determined that there is no need for passenger cars to travel faster than 180 km/h, and therefore they are equipped with a device called a speed limiter that prevents them from going beyond 180 km/h.