Samut Prakan police arrested 78 motorcyclists and seized 85 motorcycles allegedly modified for road racing.
Police manned checkpoints on major roads in Samut Prakan on Friday night until the early hours of Saturday and made the arrests.
Samut Prakan police chief Pol Maj Gen Nithithorn Jintakanon said 25 of the 78 arrested motorcyclists are under 18 and two of the 78 tested positive to drug abuses.
The alleged drug abusers will be sent for mandatory rehabilitation while those under 18 will be sent for an attitude adjustment in a military camp for seven days while the rest were fined, Nithithorn added.
Police also checked 26 motorcycle spare parts shops and found that one shop sold exhaust pipes that were illegally modified to make noises louder than allowed by the law. Twenty-one illegally-modified exhaust pipes were seized from the shop, Nithithorn said.
He added that police also found 18 big-bike motorcycles making noises louder than allowed by the law so they were prohibited from use for 30 days.