It was the first day of a weeklong campaign organised by the department and other relevant state agencies aimed at lowering fatal accidents during the New Year holidays.
It said a total of 524 traffic accidents happened on December 29, resulting in 42 deaths and 565 injuries.
Most fatal accidents were caused by drink driving and speeding (29.77%).
Motorcycle is the vehicle that engaged in most fatal accidents or 83.09%.
It said most fatal traffic accidents happened on the straight sections of highways (58.21%), on secondary highways within the districts (38.17%), and within the rural roads in the villages (32.25%).
The time of highest traffic accidents are between 16.01- 20.00 hrs, and most victims are in working ages (52.88%).
Highest traffic accidents were reported in Chiang Mai with 21 cases yesterday.
But highest fatal accidents were reported in Pathumthani province with four deaths.