The Philippines is under a nationwide smoking ban under Executive Order 26 (E.O. 26), which revolves around smoking in public places. E.O. 26 does not include private vehicles, which are not considered an enclosed public space. The Executive Order, however, does not define smoking in private vehicle with the windows down as smoking in public. This is a point of contention as it’s almost the same as smoking in public, but as the EO allows, smoking inside a vehicle is indeed legal.
However, there’s a catch to this and it involves public utility vehicles.
Under the Appendix 1 of Republic Act 10930, there is a violation listed under Light Violations where it states that "Failure to display No Smoking and/or allowing personnel or passenger to smoke inside the vehicle." Failure to do so results in 1 demerit point.
This means that smoking in a public utility vehicle violates both R.A. 10930 and E.O. 26, and are punishable by both. For PUV drivers, this means they may receive double penalties under the impending demerit system of the LTO if they allow or fail to display a No Smoking sign in their vehicle.
The executive order includes a definition for a public place as "all places, fixed or mobile, that are accessible or open to the public or places for collective use, regardless of ownership or right to access, including but not limited to, schools, workplaces, government facilities, establishments that provide food and drinks..." This is also in tandem with its definition of "Public Conveyances" which refers to modes of transportation servicing the general population, such as, but not limited to, elevators, airplanes, ships, jeepneys, buses, taxicabs, trains, light rail transits, tricycles, and other similar vehicles.
In summary, one can smoke in their own private vehicle without breaking either law, but smoking in a PUV is subject to penalties under both.