Back when I was a small child people routinely threw trash out of the car window in the U.S. Then it was made a serious infraction backed up with a hefty, enforced fine.
Within a few years it stopped and the roadsides were clean. That is the only way to stop it. Make it very painful in the wallet to do it.
The remaining small amount of roadside litter here (U.S.) now mostly comes from improperly tarped open-bed vehicles.
Local Hua Hin and regional Thailand news articles and discussion.
My brain is like an Internet browser; 12 tabs are open and 5 of them are not responding, there's a GIF playing in an endless loop,... and where is that annoying music coming from?