How are vehicles able to enter and leave the expressway without stopping?

Vehicles are able to enter and leave the expressway without stopping primarily through the use of exits. Exits are specifically designed ramps that allow vehicles to safely transition off the expressway, enabling drivers to reduce their speed and access local roads or highways without interrupting the flow of traffic. This design minimizes the need for stops, which is crucial for maintaining high speeds and reducing congestion on the expressway.

The other choices do involve vehicle movement or roadway interaction but do not facilitate the seamless entry and exit of vehicles onto an expressway. For example, traffic lights are commonly found on regular streets to control traffic, but they can introduce delays that are contrary to the expressway's goal of maintaining smooth flow. Pedestrian crossings are intended for use by pedestrians, not vehicles, and do not play a role in expressway operations. Service roads exist to provide access to properties alongside the expressway but do not serve as direct points for vehicles to merge onto or diverge from the main expressway lanes. Therefore, utilizing exits is the most effective and efficient method for enabling vehicles to enter and leave expressways.