The most serious traffic accidents for pedestrians occur on **conventional roads**. This is because on these roads, which are outside cities, vehicles tend to travel at **higher speeds**. When a pedestrian is hit under these conditions, the injuries are usually more severe and there is a higher probability that the accident will be fatal.

In contrast, within cities, although pedestrian accidents are more common, vehicles tend to go slower, which reduces the severity of injuries. Additionally, on highways and expressways, although vehicles also travel fast, there are fewer pedestrians, which decreases the frequency of these accidents. Therefore, the combination of high speed and the presence of pedestrians on conventional roads is what makes accidents more serious on these roads.