Research in 1969 by J. J. Leeming showed that countries driving on the left have a lower collision rate than countries driving on the right. Logic: It has been suggested that this is partly because humans are more commonly right-eye dominant than left-eye dominant. In left-hand traffic, the predominantly better-performing right eye is used to monitor oncoming traffic and the driver's wing mirror (side mirror). in an RHD car (that drives on the left) with manual transmission, the driver has the right hand, which for most people is dominant, on the steering wheel at all times and uses the left hand (and left foot) to change gears. So it seems driving on the left is safer, but is it natural? yes it is as we know that Cyclists, motorcyclists and horse riders typically mount from the left-hand side, with motorcycle side stands almost always located on the left. So it is natural for a passenger to sit in a car from left side. Further more; In road racing , mo