Duterte said this as the Land Transportation Office reported that 60 percent of motorcycles in the city are not registered.
Lawyer Gomer Dy, LTO chief, said at least 50 percent of these unregistered motorcycles are driven by minors and drivers without license.
Dy and the mayor discussed the issue Sunday at the "Gikan sa Masa, Para sa Masa" (From the masses, to the masses) television program over ABS-CBN.
Duterte ordered a deeper public discussion on the city's traffic system as it has implemented the P140-million new traffic signalization system since December.
Dy said motorcycle drivers figured in most traffic violations. He said dealers are also to blame for allowing buyers to bring the vehicles with them even if these are not registered.
Duterte said he will issue an executive order to stop this practice.
"You [dealers] will be charged as part of the violation. At the very least you are part of the civil liability," he warned.
The mayor ordered a crackdown on unregistered motorcycles last year amid rising cases of killings and other crimes involving motorcycle-riding men.
Motorcycles ply the streets of Davao like taxi cabs at night time.
Dy said last month motorcycles composed majority of at least 360,000 vehicles in Southeastern Mindanao that are not registered with the LTO.
LTO, which regulates vehicles and issues licenses to drivers, warned the non-registration of vehicles is posing danger to the public, as it could not be determined if they are safe to use and if their drivers are licensed.
Human rights groups also pointed out that perpetrators of summary killings in the city used motorcycles without plate numbers. (Walter I. Balane/MindaNews)