I do not think anyone should be able to drive while under the influence of marijuana even if they are not under the immediate effects. It significantly delays your reaction time and is overall just a completely unsafe idea. If you are going to smoke marijuana do not plan on driving.
After using marijuana, via smoking, it stays in your system for an extended period of time, while the true effects of the high go away fairly quickly. Once this initial high has passed, marijuana no longer effects a persons ability to drive. If a person attempts to drive while still high, they are more likely to drive in a conservative and slow manner.