Frequently Asked Questions

Importance of Drainage

Before any questions are asked, it is important to discuss the importance of drainage.

Roads need to support the trucks driven on them. Dry dirt is fairly strong. It will support a significant amount of weight. Dirt quickly loses strength when it becomes wet, which is why drainage is so important. Most of our work is focused on getting water away from the road without allowing infiltration of underlying soils.

Crown

The most basic element affecting roadway performance we can control is crown. Water goes downhill, so it does not get off the road as freely when there is a flat area. In areas the water doesn’t get off we tend to have more potholes. We try to keep a minimum of 4% crown. On a 28 foot wide road a 4% crown means the edge of the road is almost 7 inches lower than the center. Although it is important to have drainage, drivers may not feel as comfortable if there is too much crown. For that reason we try to have a maximum 6% crown, which leaves the edge about 10 inches lower than the center. In areas where we have thrown a lot of loose material to the center we will exceed 6% with the understanding the traffic will soon pack the center of the road and bring it down closer to 6%. A crown of 4%-6% is generally recommended by experts.

Importance of Drainage

Before any questions are asked, it is important to discuss the importance of drainage.

Roads need to support the trucks driven on them. Dry dirt is fairly strong. It will support a significant amount of weight. Dirt quickly loses strength when it becomes wet, which is why drainage is so important. Most of our work is focused on getting water away from the road without allowing infiltration of underlying soils.

Cutting Berms

Roads have crown to drain water to the side of the road, but water still needs to get into the ditch. If water doesn’t drop down into the ditch where we want it to run, it will drop into a ditch it makes for itself, in a washout along the side of the traveled portion of the road. Grass tends to grow up along the side of the road. This grass collects additional dirt. This dirt will end up being higher than the road, preventing water from reaching the ditch. We don’t blade dirt berms out into the ditch as that would fill in the ditch in short order. Berms are bladed up onto the road. There are usually large clumps of sod and a significant amount of dirt. We leave these clods in a windrow along the side of the road (about 1’-3’ from the edge) to allow the sod to decompose. The windrow is then spread across the road after 1-2 weeks. The dry dirt will essentially turn to dust and traffic will cause it to become airborne. The pieces of sod may still be uncomfortable to drive on for a period. Although we don’t like driving on it, this sod must be removed from the side of the road for the road to properly perform.

Blading Technique

When motor grader operators perform normal blading they drive on the right hand side of the road. The operator uses the moldboard to cut material and deposit it in a windrow at the center of the road. The cutting is intended to establish the proper crown and remove imperfections from the roadway, such as potholes and wheel tracks. Several miles may be cut successively. On the return trip the operator drives on the opposite side of the road and spreads the windrow across the side that was not cut. This loose material will temporarily fill in imperfections on the side that is not cut. The next time the road is bladed the operator will make a point of cutting the side that was not previously cut and repeating the process.

Some roads have deep potholes or corrugations (rumble strips near stop signs) and require more aggressive blading. More aggressive blading may encompass a pass in each direction with the scarifier in order to get under larger potholes or corrugations. The next pass involves cutting each side and depositing the loose material to the center of the road. The next and final pass involves spreading the windrow out on each side. This operation clearly takes more time than normal blading. In order to provide some attention to all roads sooner, we direct operators to perform aggressive blading only after all other roads have been bladed normally.

There are many names for the rough area that occasionally develops before a stop sign, including washboard, rumble strips, corrugation, chatterboard, etc. Grader operators do not cause it. Washboard is caused by vehicles that are excessively accelerating or decelerating. Pickup trucks are the biggest culprit. As the pickup excessively accelerates it spins on the rock. If there is any type of irregularity on the road the tire will start bouncing, throwing material every time it makes contact with the road. A similar action takes place while braking too much.

Washboard will develop any place people slow down or speed up, including at stop signs, curves, and occasionally at a driveway. Once it begins to develop, everyone using the road is affected. Grader operators require favorable weather conditions to cut underneath the washboard, but it will quickly develop again unless drivers regulate their behavior.

We don’t like to have windrows along roads, but sometimes they are necessary. For example, windrows are temporarily created in the center of the road while blading, but are spread out before the end of the day. They are also used to give sod a place to decompose before it is spread across the road. Outside of storing decomposing sod, the sole purpose of a windrow is to collect loose rock that is not able to work into the roadway. Loose rock will not work into the road when it is frozen in the winter or during a dry spell in the summer. In these circumstances the loose rock may either be bladed off while pushing snow or rolled off the road by traffic, so we collect it into a windrow to preserve it for future usage. When proper moisture returns the loose rock is to be spread across the road to encourage it to work in.

New concrete bridges have a crown built in them, but older bridges were built flat. New timber deck bridges are still built flat. The flat deck requires the approaching roadway to be flat; flat roads encourage potholes. The same thing happens where the rock road meets the pavement. The approaching roadway has to transition from a normal crown to being flat where it touches the edge of the pavement. Again, flat areas tend to encourage potholes.

Driveways need to be shaped to meet the road; the road should not be shaped to meet the driveway. Too often the crown on the side with the driveway will become flat or tipped the wrong direction as it goes over the driveway. For a vehicle passing the driveway the crown changes before and after the driveway, causing the vehicle to be thrown around some. Improper crown going through the driveway causes water to either sit on the road or run down the middle of it. The crown should be carried through the driveway on both sides of the road. Operators will occasionally reshape the road, causing the driveway to be undercut. The drop created needs to be fixed. If it is not fixed, please contact the road department so we can direct it to be fixed.

Weight limits are placed to allow us to continue usage of old bridges in a safe manner. The posting indicates the maximum gross weight of a vehicle. It takes into account the fact that longer trucks may not have all axles on the bridge. Exceeding the posted limit exposes the operator to significant liability, and endangers the operator and other vehicles on the road.

Poweshiek County has 255 bridges, of which 50 have some type of weight restriction. One half of our bridges were built before 1970, with several being built before WW I. We attempt to keep these usable and to replace them as funds permit, but the average cost of replacement is roughly $200,000. We use an objective set of criteria to determine the order in which bridges are replaced. Similarly we use an objective set of criteria to determine which bridges we work on. The choice between replacement and repair is generally dictated by specific conditions of a given bridge.

The Iowa DOT is able to provide 24-hour snow removal service on Interstate 80. Poweshiek County does not have the resources in equipment or labor to accomplish the same. Also, county pavements were not designed with the same geometrics; they are narrower, the foreslopes are steeper, the curves are sharper, etc. Rock roads are much more problematic. At times the snow is level from fence to fence, with no indication of where the road or ditches are. It is difficult enough to plow such a road in the daylight. Working in the dark unnecessarily increases the chance of damage to equipment and exposes operators to additional risk. Operation in the dark is limited to emergencies.

Obstructions

We try to keep the roadway as safe as possible. We don’t want drivers to run into an object that would cause them to come to an immediate stop. We limit the existence of these fixed obstacles on the roadway. When we can’t remove a fixed obstacle from the roadway (for example, a bridge) we often place a guardrail to lessen the severity of an impact.

We work to keep the roadway safe, but we recognize vehicles occasionally leave the roadway and go into the ditch. We are obligated to accommodate power poles in the ditch, but try to minimize the hazards of fixed obstacles by removing any that are not necessary. Retaining walls around culverts are generally built in a way that would cause them to act as a fixed obstacle. A vehicle striking the retaining wall would stop abruptly, increasing the chance of injury. If residents wish to improve the area around their culvert they have an option of placing a metal apron, which is acceptable for use in the ditch.

Chapter 318 of the Iowa Code prohibits obstructions in the right-of-way, and requires the county to have them removed. It also prohibits fences along the edge of the road, which is occasionally done to allow livestock to graze the ditch. In accordance with the Code, any work performed in the right-of-way requires a permit from the agency in charge of the road.

Trees and brush look nice, but they are not something we want in our ditches. They increase the collection of drifting snow, provide shade that prevents ice on the road from melting, obstruct visibility, get in the way of many maintenance activities, create hazards when branches fall, and present a hazard to vehicles that leave the roadway. When time is available we work to remove trees from the road right-of-way. Individuals are free to do as they please on their private property, but we work to prevent new trees from being placed in the right-of-way. Smaller plantings like native grasses and flowers do not present a hazard and are acceptable.