The example of a "busy highway" is often used in noise assessment for traffic. The "busy" part of the example refers to enough density of vehicles that sound is emanating from every point along the highway. Maybe you guessed a train, which is a possible example except that the locomotive may emit more energy than the cars.

As for which source (point or line) will be louder, the answer is the line source, as will be explained in the next paragraphs. For now, just think of the sound coming at you from a wide range of directions, not just one.