So common peoples way of avoiding being pulled over while smoking a joint while driving or in your car (where your car would smell) is that to smoke a joint at home before you head off to your jouney, that's about to change in UK http://www.honestjohn.co.uk/news/miscellaneous/2015-01/police-to-deal-out-roadside-drug-testing-in-2015/ I'm not sure if other countries do it but this is the first in UK, they usually do it in station not road side so you have slim to non chance of evading.