We have a 20 foot wide gravel over shale access driveway that is side by side with a neighbors 15 foot wide gravel over shale driveway such that it appears to be one 35 foot wide gravel street.
There are three homes that share the 20 foot wide portion and there is one house that owns the 15 foot wide portion. The length of the shared section is about 220 feet to where the 20 foot wide side ends and the 15 foot wide side continues on another 300 feet to the last house. We live in the first house off pavement.
We and the residents of two other homes that use our 20 foot wide side all drive slowly on the gravel, mostly to try to keep dust production minimal.
One of the residents of the home accessed by the 15 foot wide side (a Woman who will go unnamed) likes to drive faster on her side. Curiously her side develops a washboard surface (as does a particular spot on our side where she crosses over onto our side) whereas our side remains smooth. Periodically one of her male relatives comes over and smooths out the washboard with rake and shovel. It reforms the same as before after a couple of months.
The drivers on our side probably stay in the 5 to no more than 10 mph range. I estimate that the faster driving neighbor is typically moving at 15 - 20 mph. She also generates a fair amount of dust in the dry season.
My conclusion after years of observation of this "phenomena" is that the development of the washboard is related to slipping of the drive tires and bouncing of the suspension. It seems there is a threshold speed above which the wash boarding forms and then gets worse and worse.
P.S. She is a nice lady in most all regards but refuses to slow down even though we complain about the dust she generates. I refuse to help her male relative smooth out the washboard because it slows her down once they develop. I have explained this all to him and he understands and knows I will help him with most anything else he needs a hand with.
I display my joy at seeing her suffer from her self induced annoying ride, when I am outside and see her bouncing along, by smiling at her and waving as she drives by.
Edited by ckent323, 19 June 2018 - 06:09 AM.