Definition
- LHD=Left handed driving
- RHD=Right handed driving
- LHT=left handed traffic
- RHT=Right handed traffic
- LH=left handed
- RH=right handed
The terms right and left-handed driving refer to the position of the driver and the steering wheel in the vehicle and are, in automobiles, the reverse of the terms right- and left-hand traffic. The rule also includes where on the road a vehicle is to be driven, if there is room for more than one vehicle in the one direction, and the side on which the vehicle in the rear overtakes the one in the front. For example, a driver in an LHT country would typically overtake on the right of the vehicle being overtaken.
In LHT, traffic keeps left and cars usually have the steering wheel on the right (RHD: right-hand drive) and roundabouts circulate clockwise. RHT is the opposite: traffic keeps right, the driver usually sits on the left side of the car (LHD: left-hand drive), and roundabouts circulate anticlockwise.
Most low-beam headlamps produce an asymmetrical light suitable for use on only one side of the road. Low beam headlamps in LHT jurisdictions throw most of their light forward-leftward; those for RHT throw most of their light forward-rightward, thus illuminating obstacles and road signs while minimising glare for oncoming traffic.
When it comes to auto parts, the sides are determined by the position of the driver in the vehicle, facing forward. Meaning, looking over the hood, and sitting in the driver’s seat, your left hand is the left side, your right hand is the right side.
If you walked into a local parts store, say in the USA, where 99% of the vehicles are left hand drive (LHD), they will usually ask if you need a part for the driver or passenger side. If they sell you a part for the Driver side, it will be for the left side.
In Australia, the same question at their local parts store would be the opposite, their Driver side would get you part for the Right side.
And for auto lamps, it is :
LHD=RHT, LH=left side=driver side, RH=right side=passenger side
while RHD=LHT, LH=left side=passenger side, RH=right side=driver side;
both based on the driver in the vehicle, facing forward.