09/04/2026
UNDERSTANDING GRAVEL ROAD MAINTENANCE
Washboarding is one of the most common complaints about our gravel roads. Although a grader can smooth the road, washboards can return quickly when the underlying material is not suitable for a long-lasting road surface.
WHY DO WASHBOARDS FORM?
Vehicle tires repeatedly push and bounce loose gravel into small ridges. Washboards develop faster when:
* The road is dry
* Traffic is heavy or traveling too fast
* The gravel does not contain enough fine binder
* The particles are mostly the same size and do not lock together
* The road surface is not adequately compacted
* Existing washboards are not cut to their full depth
A road may have been graded recently and still develop washboards again. This does not necessarily mean the operator failed to maintain it. It often means the existing material will not stay bound together.
NOT ALL GRAVEL IS ROAD-SURFACE GRAVEL
Good road gravel contains a properly graded mixture of larger rock, smaller rock, sand, and fine binder material.
For example:
* Gravel with too few fines stays loose and develops washboards.
* Material containing too much clay may become dusty when dry and muddy when wet.
* Gravel containing mostly one particle size does not lock together properly.
* Properly graded gravel contains different particle sizes that fit together and enough binder to hold the surface in place.
The Department is often working with locally available soils and lower-grade gravel from our pit. A grader can reshape this material, but it cannot change its quality or add the missing binder.
WHAT WOULD CREATE BETTER ROAD CONDITIONS?
Longer-lasting improvements would require:
* Testing the existing soil and gravel
* Improving or stabilizing weak soil beneath the road
* Trucking in better soil, binder, or higher-grade surface gravel
* Adding the correct amount of moisture
* Properly compacting the new material
* Maintaining an adequate crown and drainage
* Placing enough gravel to replace material lost through traffic, weather, and maintenance
For a typical 24-foot-wide road, one mile would require approximately 3,750 tons of material. That is nearly 190 truckloads if each truck carries 20 tons.
Based on current regional material, trucking, equipment, and labor costs, properly improving one mile would cost approximately:
$250,000 PER MILE
That is a general planning estimate. The cost could be lower when suitable material is nearby or higher when it must be hauled a long distance.
If the soil and road base underneath also need to be removed, stabilized, or rebuilt, the cost could reach $500,000 or more per mile.
For perspective, properly improving only 10 miles could cost approximately $2.5 million.
STAFFING ALSO AFFECTS FREQUENCY
A realistic maintenance assignment would be approximately 10 road miles per operator. Tribal Roads Operators are responsible for more than 50 + miles each. That is over five times the desired coverage, before accounting for travel, weather, equipment breakdowns, repairs, and other road-maintenance responsibilities.
Technical references: NDDOT Gravel Surfacing Specification and FHWA Gravel Roads Construction and Maintenance Guide
