Under what conditions is it illegal to drive?

Driving under the influence of drugs or alcohol is illegal because it significantly impairs a driver's ability to operate a vehicle safely. When a person is under the influence, their coordination, reaction times, and judgment are compromised, which increases the risk of accidents and endangers not only the driver but also passengers, pedestrians, and other road users. This is why laws are strictly enforced regarding blood alcohol content (BAC) limits and the use of controlled substances while operating a vehicle. The legal framework surrounding DUI (driving under the influence) suggests that this offense is one of the most serious traffic violations due to its potential for severe consequences, including accidents and fatalities.

In contrast, wearing headphones or being distracted by a passenger, while problematic, do not carry the same level of legal sanction as driving under the influence. Furthermore, driving below the speed limit is not illegal and is often encouraged as a safe driving practice unless it's impeding traffic flow or violating specific road conditions.