How does radius posting work?

How does radius posting work? When posting a truck, you may enter the distance you are willing travel from your starting point in order to pick up a load. Also, you may enter the distance are you willing to drive from your destination point to drop off a load. For example, you can post a truck in Houston, TX with radius 90 miles going to San Francisco, CA with radius 40 miles. Radius truck posting broadens your posting and therefore allows you to find more freight to haul.