The **longitudinal markings** on roads are lines that extend along the roadway and have different meanings depending on their type. A **continuous line** is one of these markings, and its main function is to prohibit drivers from crossing it or driving over it. This is because it indicates a movement restriction, generally for safety reasons, such as in areas with low visibility or where changing lanes could be dangerous.

When we encounter a **longitudinal marking consisting of two continuous lines side by side**, its meaning is the same as that of a single continuous line. This means that these lines should not be crossed or driven over, reinforcing the prohibition and increasing road safety.

Therefore, the correct answer is that a longitudinal marking of two continuous lines side by side has the same meaning as a continuous longitudinal marking, as both indicate a movement restriction for vehicles.