A road has many influences that factor into how it is used as well as how efficient it is. In order for a road to become and official road, it has to have some sort of traffic. It must have a destination. So simply put, traffic (cars) make up a road. The road then influences the speed of the cars traveling. Depending on the size (capacity) of the road, influences the speed as well as the traffic. The speed limit of the road determines the wear and tear of the road and the amount of repairs it receives. A road with less traffic will take longer to fall into disarray and most likely stay unmaintained for longer periods of time. A road with higher traffic and speeds will be maintained more. However, higher speeds mean higher accident rates. More accidents means more traffic. Other factors that determine how a road can be used is the type of development around the road and the route of the road itself. A residential area causes for lower speeds than a more commercial area. The route of a road can affect the speed and as well as the amount of accidents. A windy road that has many blind turns and on a mountain side will have a lower speed as well as a higher amount of accidents (depending on traffic) than a straight forward road with the same amount of traffic and speed.
There are plenty of other factors that influence the use of the road and the outcomes. This was a simple diagram to show you that every element interacts with at least one other element to affect the overall system. To create a larger more complex system, we could talk about how weather conditions could affect the use of the road over a short period or over a longer period leading to the degradation of the road.