Final answer:
Trucks are required to stop at weigh stations on highways to ensure they are not overloaded, which helps maintain road safety and infrastructure. While at weigh stations, secondary checks for illegal substances or contraband may also be conducted.
Step-by-step explanation:
Trucks must stop at all weigh stations on the main highways primarily for the reason that they can be weighed to determine if they are overloaded. This is important for several reasons, including road safety, infrastructure preservation, and legal compliance.
Overloaded trucks can cause more wear and tear on road surfaces, increase the risk of accidents due to tire or mechanical failure, and thus pose a significant risk to both the driver and other road users. Additionally, by enforcing weight limits, authorities can protect bridges and overpasses from potential damage that could be caused by excessive weights.
While the primary purpose is to check for weight compliance, these stations can also serve secondary functions. For instance, law enforcement officers at weigh stations may use technologies like gamma ray-, x-ray-, or neutron-scanning devices to reveal the contents of trucks, which can help in detecting illegal substances or contraband. However, these are supplementary checks and not the main reason for the existence of weigh stations.