Have you ever thought about a road? It is something one does not usually give much thought to outside of coming across traffic congestion or the occasional pothole.
Road are designed to have a pitch that allows water and debris to flow to the gutters. This is great as the gutters flow into sewers and keep the streets clutter free. There is a bit of wear that build up over time near the edge of the gutters, but since traffic drives in the middle 90% of the road the wear does not impact the average driver. Who it does impact is pedestrians, when sidewalks are not in place.
The same small break in the road that a truck or car would glide over can cause a pedestrian to lose balance or fall down. This is especially true of our children or retired neighbors whose balance is compromised due to their life stage. Something to think about next time you are driving around and notice a neighborhood which lacks sidewalks.