I am up and down the 304 regularly from Si Maha Phot to BKK.
Some of the 304 is duel cartridge way and some 3 lanes. Its got its good sections with smooth running and good lighting then you come up against sections with no lighting and for about 5km in some sections, you can't use the nearside lane as it's so bad you risk damaging your vehicle or motorbike.
If like me you use it regularly you know where to avoid the worst parts. You effectively drive along lane hopping all over the place to miss potholes etc.
Then there are sections where there is lighting but its never on, could be faulty or not wired up or the local authorities trying to save a few baht even.
So with all that said couple that lot with Thai drivers on their phones, badly maintained busses and trucks, scooters with no lights on, vehicles on the hard shoulder driving the wrong way against the flow of traffic, , u-turns you got a challenge alright 555.