The greatest danger that people experience when driving on expressways is the potential for a rear end collision.
The reason this greatest danger exists on expressways is some people don't leave enough room between their vehicle and the vehicle in front of them for an emergency stop.
Should the vehicle in front of you have to suddenly come to a stop then you could end up plowing your vehicle into the rear end of the vehicle in front of you.
Always stay a safe distance back from other vehicles when driving on the expressway so you'll be able to safely stop if you need to suddenly and always be alert.