They didn't. Right hand vehicles are still the norm in most non-North American countries.
Left hand drive.
No
RHD is Right Hand Drive, as in vehicles where the driver sits on the right hand side i.e mail vehicles.
Right hand drive, or RHD, vehicles can be bought at government auctions. There are also dealers who specialize in the sale of RHD jeeps and other vehicles. RHD conversion kits can also be installed on conventional left hand drive vehicles.
You may drive left sided vehicles. You may not drive them on the right hand side of the road.
In Singapore, cars and other vehicles drive on the left of the road, as we do in Britain. This was due to its British past colonial history. So the steering wheel will be on the right as in vehicles in Britain. I believe that any vehicles with left -hand drive have to display a notice on the rear warning that they are a left-hand drive vehicle.
The right side would be the passenger side in left-hand driver organized vehicles. In right-hand drive-organized vehicles, it would opposite.
The flow of traffic is on the left-hand side of the road, but vehicles with the drivers controls on either the left or the right are lawful.
On a left hand drive vehicles, it is on the front right side behind the right headlight
Most countries have laws requiring vehicles to stay on the right hand side of the road, so left-hand-drive vehicles sell far better in most of the world than vehicles with the steering wheel on the right side of the vehicles. This would include the United States, Canada, all of South America, Europe and most of Africa.
I've seen plenty of right hand drive vehicles in Colorado so I'm sure it's fine, you can always give your local DMV a ring and ask though!
The UK doesn't, it drives on the left as does about a third of the World (most being ex British Colonies with the major exception of Japan). You are probably getting confused with right hand drive vehicles which the UK uses, placing the driver in the middle of the road and giving the best view for overtaking. Similarly people who drive on the right have left hand drive vehicles, this was part of the justification for Sweden changing as most of their vehicles were left hand drive as well as their neighbours drove on the right with left hand drive vehicles. A number of countries have switched from left to right but the Japanese after looking at the time (4 years of preparation) cost and chaos caused in Sweden when it changed decided not to try it! The custom of keeping to the left originated from the use of the horse (mounting easier for right hand person on the left) and the wearing of swords (keeps the scabbard from clashing as you pass and the sword away from your enemy).