Final answer:
Truck drivers must check the security of their cargo within the first 50 miles of their trip to ensure safety and compliance with regulations.
Step-by-step explanation:
Drivers of trucks and truck-tractors must check that the cargo is all secure within the first 50 miles of the trip. This is essential for safety reasons as the initial portion of a trip can reveal issues with the cargo's security due to changes in speed, direction, and road conditions that could potentially cause the cargo to shift. It is also a regulatory requirement in many regions for drivers to perform such checks to ensure that they comply with safety standards.