What feature helps reduce the risk of vehicles crossing into opposing lanes on expressways?

Barriers or medians are designed specifically to prevent vehicles from crossing into opposing lanes on expressways, significantly enhancing road safety. These features create a physical separation between lanes of traffic moving in opposite directions, which helps reduce the likelihood of head-on collisions that can result from vehicles accidentally straying into oncoming traffic.

Traffic lights and access roads are not typically used on expressways, as they are more common in urban or residential areas where intersections are necessary. Rumble strips serve a different purpose; they alert drivers through noise and vibration when they are drifting out of their lane or approaching a hazard, but they do not provide a physical barrier to prevent lane crossover in high-speed conditions like an expressway. Thus, barriers or medians provide the most effective protection against vehicles unintentionally entering opposing lanes.