Daily police patrol enforcement of driving laws and behaviors, start writing tons of tickets, start towing illegally parked cars, tow away vehicles that are uninsured/unregistered/unroadworthy, arrest and tow anyone driving without a license. Fixing the problem is easy, all they have to do is get the lazy RTP mafia to go out and do their jobs. The longer the lawlessness goes on the worse things will get, and Thailand is one of the worst in the world for road safety. The WHO has already commented on it, and the lack of follow through by the Thai government is well known.
https://www.who.int/thailand/activities/ccs-roadsafety