You don't need to become an expert in road design just because you're in charge of hiring a team to create private roads for a housing development, but it does help to understand some of the basics. Knowing what a well-designed road needs allows you to double-check the proposal made by a road construction crew so you don't end up wasting money on an access way that fails after only a few years. Whether you're looking to add dirt, gravel, or paved roads, they all need the right crowning to last.
What is Road Crowning?
Most people assume that roads are flat, but they're actually curved so that the center point is higher than both sides. This is known as the crown, so obviously applying the necessary shaping to the road as it's being made is called crowning. Most crowning is basically invisible, but dirt roads with little gravel coverage often need such a high slope that it's easy to see the gentle curve.
Why Does Crowning Matter?
A perfectly flat and level road does not drain quickly enough for safe driving conditions. Not only does standing water on a roadway cause accidents, it also damages the road by directly eroding gravel roads or dissolving the bonds holding the materials together on a paved surface. In fact, it's estimated that about 90% of the issues with roadways are caused by moisture. Without proper drainage, your road will quickly develop ruts, potholes, collapsed shoulders, and other serious problems that are costly to fix. No amount of sealing cracks and filling potholes can permanently fix a road that has drainage problems.
How Much Crowning Is Necessary?
There's no magic number for sloping that will work for every road. Experienced road installation crews can determine the perfect amount of slope for crowning your road based on the specifications, but some general guidelines include
- About 1/2 inch of rise on gravel roads for every foot of width in a lane, which is 5 inches of rise for a road with two 10 foot wide lanes
- Only 1/4 inch of rise for the same distance on a paved road, resulting in a 2 1/2 inch rise on the same width
- An increase of at least 1/4 of an inch of rise per foot when the road is sloped to prevent water from running straight down the lanes.
Of course, some gravel roads need 3/4th of an inch of rise for the crown to work properly, while paved roads can also need more than just 1/4th of an inch. This is why it's essential to choose a road construction company that has the engineering skills to consider all the other factors affecting drainage before settling on the perfect amount of slope for your road.
How is Crowning Done?
You can't just pour on a little extra asphalt in the middle of the road and watch it magically settle into a smoothly curved slope. Paved roads must be built from the graded dirt up so that the rise is incorporated in every layer of material. Failing to do this can cause the surface of the road to sink down and crack due to a lack of support.
Since gravel roads are cut directly into the dirt before being covered, the crown is cut with the clearing and grading equipment. An attachment called a moldboard allows the operator to carefully pack and move dirt to create a gentle and even slope. It takes a very experienced heavy machinery operator to create a perfect crown in one pass, so most crews work in sections and verify the dimensions with laser levels before moving on to the next area. If you're looking for a company to construct roads for you, check out one like Lien Transportation Co.