Mr Chadchart wrote on his Facebook page that he boarded both inbound and outbound trips of bus route No.8, which runs between Happy Land in Bang Kapi and Phra Phuttha Yodfa bridge (Saphan Phut), to experience its service first-hand.
"The drivers were not speeding much (probably because of heavy traffic)," he said in his posting in Thai.
"The bus conductors told me that they have no salaries and they earn money from the tickets sold," the minister wrote.
"This is why they have to race and get as many passengers as possible, and they're working from 5am to 5pm."
In contrast, Bangkok Mass Transit Authority (BMTA) employees have monthly salaries and also earn some money from the tickets sold, he said.
He attributed the poor bus service to the overall mismanagement by joint private-public bus route operators.
Half of the city's buses are jointly managed under franchises by the public and private sector, while the other half are overseen by the BMTA. The management will have to find ways for them to co-exist and improve the quality of the service, he added.
According to Mr Chadchart's Facebook poll on the quality of service by Bangkok buses, route No.8 was voted the poorest service with 223 votes, followed by route No.44 (31 votes), route No.1 (23 votes), routes No.16 and 92 (18 votes) and routes No.75 and 122 (17 votes).
On Thailand's popular webboard pantip.com, internet users also criticised the notorious bus route No.8.
"If you want the bus to stop at a bus stop, it will stop at the next one. The bus won't slow down when it's going down a bridge and it will go full throttle from midnight onwards," Pantip.com user 888324 said.
Another Pantip.com user going by the name Mr Pandajungk said, "I don't know if I'm riding a bus or a roller coaster anymore!"
"Bus route No.8 is legendary. When I'm in a rush, I'll ride it," commented an internet user going by the alias Jacob MICRO.
"Some of the No.8 buses are painted pink, but the service is still from hell," internet user Phmatzue wrote on the webboard.