Every car is supplied by ash-tray, but sometimes it's uncomfortable to look aside and throw off the ashes into it. Moreover, as far as I know there are people who smoke not taking a cigarette out of the mouth. So, for these very smokers I want to offer a nice idea of a special ash-tray!
Do you remember how parents tuck a napkin under their baby's chin?! So, the principle of a whole new ash-tray is similar working! You should tuck a special napkin with hollow to which ash will fall under your chin. The ash-tray may be done of plastic of some other material, the most important is that it resists heat. Using such breast ash-tray, your hands will be free, so your attention to traffic on road wouldn't be dispersed on minor things…
In general I would strongly recommend you not to smoke at all. I think our health is worth this "sacrifice", but if you find some pleasure in smoking, hope my idea would be to your taste!