As spring arrives and the snow melts, we’re reminded of the fragility of our transportation infrastructure in Cook County. Many of our roadways are improved cart paths and logging roads built over swamps and rock. Water – the natural enemy of a functional roadway – finds the weakest spots in our county road system. Here’s how it starts:

Frost heaves and boils. Throughout the winter and spring, water freezes and thaws within the roadbed. As the temperature drops in fall and winter, the layers of the roadway freeze in layers called ice “lenses.”  Differential frost heaves can occur around culverts bedded in poorly drained base materials, forming seasonal dips and heaves.

Spring rolls around and the roadway thaws from the top down. Water trapped above the still frozen subgrade can “boil up” and find a path to the surface in the weakest spot. Frost boils then appear as sporadic wet, soft areas on otherwise dry, firm gravel roadways and are often an indication of weak subgrade. In terms of maintenance, there’s not much we can do except keep heavy truck traffic off a road and let it “heal.”

Frozen culverts.  Culverts move water under the roadway. Culverts exposed to cold air often freeze in the winter. If frozen solid, water can pond up on one side. One of our maintenance activities is to identify a frozen culvert and “steam” it by using hot pressurized water.

Sinkholes and washouts. Despite our best efforts, water occasionally travels through the roadbed around a frozen culvert, removing material as it flows. If enough material is removed, the road collapses in a sinkhole.

Likewise, moving water can overwhelm a ditch or a culvert. When water runs over a roadway, it can wash away enough material to make it impassable. If possible, we prevent washouts by maintaining clear paths for water to leave the roadway. Still, every spring water finds its way over or around one of our older compromised culverts. When that happens, you'll see us out in our red trucks and “high vis” vests with plenty of orange traffic cones, making note of areas where repairs are needed once road conditions allow.

Our goal at the highway department is to ensure the safety of the traveling public and gradually improve the overall quality of our county roadways. In the meantime, we’ll keep mending the heaves, bumps and boils of spring.