What is required for a driver to legally park on a highway in Illinois?

In Illinois, it is essential for drivers to ensure that their vehicle does not obstruct traffic when parking on a highway. This requirement helps maintain the flow of traffic and reduces the risk of accidents that can occur from vehicles blocking lanes. Parking in a manner that obstructs traffic can create hazards for other drivers, potentially leading to collisions or congestion.

The other options may imply certain conditions but do not address the primary safety concern of ensuring that other vehicles can pass without difficulty. Therefore, ensuring that a vehicle parked on a highway does not impede the movement of traffic is a critical legal requirement for safe driving practices.