What causes washboarding on Iowa's farm to market roads?
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On August 14th 2009 Terry Hagen was headed eastbound on a gravel road when he lost control of his motorcycle, hit the guide wire in the ditch and was thrown from his motorcycle. Mr. Hagen died as a result of the injuries suffered in the accident. There is no word on whether he was wearing a helmet.
Gravel roadways in rural Iowa present much different challenges than do paved roads. First of all most of those gravel roads were constructed as farm to market roadways, meaning they were for heavy agricultural equipment with tires much larger than a motorcycle tire. Agricultural equipment tires on gravel can cause deep ruts or what I describe as sort of a rock stream bed with high sides, from where gravel has been pushed aside by the wide tires. After the rut in created a smaller tire can be forced in a direction not intended, thus causing a loss of control with a result similar to the one with Mr. Hagen.
Counties grade these roads on a regular basis, or at least are supposed to. One problem that regularly occurs is referred to as corrugation or “washboarding”. Washboarded gravel produces an uncomfortable ride and can lead to the same loss of control or having less control of a car or motorcycle. Like the surface of a washboard the gravel surface has a series of smaller ridges perpendicular to the tire’s direction causing the car or cycle to vibrate and skip as it moves over the washboard.
What causes washboarding? According to the Road Management & Engineering Journal, Preventing Washboarding, June 2000, there are several known causes.
There are several conditions that cause or aggravate washboarding on county gravel roads.
1. Lack of moisture. Rainfall reduces the occurrence of washboarding.
2. Traffic including hard acceleration or braking aggravates the condition.
3. Washboarding is most likely to occur at intersections. Cars stopping or starting can aggravate washboarding, making it far worse. Like moguls being created and moving down a ski slope washboarding is a collectively created phenomena.
4. Poor gravel quality.
What does this mean to us about how to know if we are likely to encounter washboarding on gravel roads? This tells us a great deal about how we might change our driving habits to avoid losing control of a car or motorcycle and being in an accident.
Watch the rainfall and know that if there hasn’t been a lot of rain you’re more likely to encounter washboarding. If you don’t know the recent rainfall history you can still get some idea of what the weather has been like. Look in the ditches and farm fields for standing water; if no standing water and the dirt looks dry then rain probably hasn’t fallen, meaning you’re more likely to encounter washboarding.
Second, as you approach intersections assume there is washboarding. Better safe than sorry. This means you should slow down well before the intersection ahead.
Third, slow down.
Lastly, most people won’t know the difference between good and “bad” gravel, so just assume it’s all bad gravel and drive cautiously.
For a a photo of washboard, follow the link.
One last thing about this accident doesn’t indicate to me washboarding had any effect. The diagram shows Mr. Hagan pulling away from an intersection after turning from S-14 onto 290th Street. Was it a deer or something else that caused him to lose control? We don’t know.