Why Are Residential Roads Higher In The Middle Than At The C

Why are residential roads higher in the middle than at the curb?

In residential road design, a common feature is that the center of the street is higher than the edges or curbs. This engineering feature is primarily implemented to facilitate efficient water drainage, prevent flooding, and maintain the structural integrity of the roadway. The slight incline, or crown, typically ranges from 1% to 2%, meaning that the center of the road rises approximately one to two inches higher than the edges over a span of 10 to 12 feet. This slope directs rainwater and surface runoff toward the curbs and drainage systems located alongside the road, helping to prevent water accumulation on the surface, which could lead to hydroplaning hazards for vehicles and damage to the pavement.

The rationale behind this design is rooted in hydrological and structural considerations. Proper drainage is critical in maintaining the longevity of roads, especially in areas with frequent or heavy rainfall. If roads were perfectly flat, water would collect on the surface, causing deterioration, potholes, and increased maintenance costs. By elevating the center, water naturally flows away from the surface towards installed catch basins, storm drains, and ditches. This ensures that water does not pool on the roadway, which could compromise the pavement’s structure or cause standing water that invites accidents.

Furthermore, the crown of a road helps distribute weight more evenly across the surface, reducing stress on the pavement materials. It also assists in maintaining the road’s shape over time, as water runoff keeps the surface dry and free of erosive elements. Overall, the slight elevation in the middle of residential roads plays an essential role in prolonging roadway life, improving safety, and managing stormwater efficiently, which is a fundamental aspect of roadway construction and urban planning.

Sources:

- Federal Highway Administration. (2022). Road Design Factors. Retrieved from https://www.fhwa.dot.gov

- American Association of State Highway and Transportation Officials (AASHTO). (2011). A Policy on Geometric Design of Highways and Streets.

- U.S. Geological Survey. (2020). Drainage and Roadway Design. https://pubs.usgs.gov

- National Asphalt Pavement Association. (2018). Pavement Design and Drainage. https://www.asphaltpavement.org