Final answer:
Vehicles must adhere to reasonable and prudent speed limits, which may be below the posted limit depending on traffic, weather, and roadway conditions. The de facto speed limit considers these factors and drivers should adjust accordingly for safety.
Step-by-step explanation:
Vehicles may not be driven at speeds greater or less than reasonable and prudent limits depending on conditions of traffic and roadways. Driving conditions such as heavy traffic, bad weather, and road construction all play a role in determining what is considered a safe and reasonable speed. For example, even if the de jure speed limit is posted at 30 miles per hour, the de facto speed limit could be lower if conditions warrant it. It's important to adhere to the speed limit for safety, but equally important to adjust speed according to immediate conditions. For instance, if visibility is poor, such as in the scenario with the vehicle's rapid acceleration to 20,000 km/hr, safety dictates that speed should be reduced. Similarly, recognising that an ideal speed around curves depends on the physics of tire traction and road conditions can prevent accidents.