Usually found on concrete roadways,Interstates & freeways. They are grooves imbedded in the road surface to dissapate water during heavy/moderate rains. Sometimes can go for a mile or more only to reappear again.
Depending on the tread patterern & size of the motorcycle tire,they can cause a front wheel shimmy,some more severe than others.
I've encountered them on Interstates in the West,Ca. is fond of them,& on I-81 & 70 ,WVA,I-64 around Charleston,NY & PA. in the East.
No big deal really,just relax your grip on the handel bars & you'll be O.K..