Driving a car is a high cognitive-load task requiring full attention behind the wheel. Intelligent navigation, transportation, and in-vehicle interfaces have introduced a safer and less demanding driving experience. However, there is still a gap for the existing interaction systems to satisfy the requirements of actual user experience. Hand gesture as an interaction medium, is natural and less visually demanding while driving. This paper aims to conduct a user-study with 79 participants to validate mid-air gestures for 18 major in-vehicle secondary tasks. We have demonstrated a detailed analysis on 900 mid-air gestures investigating preferences of gestures for in-vehicle tasks, their physical affordance, and driving errors. The outcomes demonstrate that employment of mid-air gestures reduces driving errors by up to 50% compared to traditional air-conditioning control. Results can be used for the development of vision-based in-vehicle gestural interfaces.