Why do some countries drive on the left and others on the right?

It is estimated that around 35% of the world drives on the left, including the UK, Australia, Japan, India, and more. In fact, around 75 countries drive on the left. While driving on the left is believed to have originated because of the Roman empire, the actual answer is a lot more complicated than that.

In a normal bi-directional traffic flow, keeping to the left or right side is essential to avoid collisions and keep the traffic flow smooth and predictable. The term left-hand drive generally refers to the position of the steering wheel. For example, if the traffic follows through the right side of the road, vehicles will be left-hand drive as the steering wheel and the driver will be positioned on the left to get a better view of the traffic, especially during overtaking maneuvers. 

Right-Hand driving countries will overtake on the left, while left driving countries will overtake on the right. As of today, 165 countries follow right-hand traffic, while 75 countries follow left-hand traffic. The whole road network is also built with traffic direction in mind, meaning roundabouts will circulate clockwise in LHD countries.

Depending on the driving side, most manufacturers produce two different configurations. Almost all automobile manufacturers, namely, BMW, Mercedes-Benz, Ford, Chevy, and more, cater to the worldwide audience, hence they produce both RHD and LHD cars. 

Other mechanical differences in passenger vehicles include wiping direction of windscreen wipers, giving priority to the driver. The windshield wiper and headlight levers will also be switched up according to the steering wheel position.  

Headlamps also get a different beam pattern. In low beam operation, the light pattern is spread asymmetrically, concentrating on one side of the road to minimize glare on oncoming vehicles. In LHD countries, the headlamps throw forward and leftward, while in RHD countries, the throw is forward and rightward. Some modern vehicles are also capable of shifting the beam direction depending on the location or a manual switch.  

As expected, the steering wheel position will also affect safety regulations in some cases, unless the manufacturer redesigns the chassis with reinforcements. 

All the archeological and historical evidence points to the Roman Empire, who used to drive their chariots and carts on the left. Since the Romans occupied most of Europe, the custom spread throughout the land including the UK and other countries.

One of the predicted reasons why they started driving on the left is because of safety. Most of the Roman population was right-handed, meaning they got on their horses from the left. Since getting on was easier if the horse was on the left side without obstructing traffic, people started riding on the left. Since the Romans built a comprehensive road network across Europe, the whole population started riding/driving on the left. It also allowed them to quickly greet other road users or whack them with swords. It also avoided the chance of scabbards hitting other road users.

Soon after, Napoleon invaded Europe and decided everyone should drive/ride on the right since he was left-handed and more comfortable on the right-hand side of the road. Some territories like the UK and Sweden who were not under the new rule continued to ride on the left.

As the 1700s came around, traffic started to become more prominent as big wagons started hauling goods across the land. Since the drivers used to sit on the horses instead of a driver’s seat and because most of them were right-handed, they were used to whipping the horses on the right. This meant they had to sit on the left horse, eventually leading to everyone driving on the right. Sitting on the left also allowed drivers to check for wheel clearance when they encountered traffic.

When the colonization of North America began, they continued to follow British tradition and started driving on the left. Although driving on the left gave the drivers a better view of the ruts and road edges, the rising traffic caused the shift, so that drivers can see the clearance between the nearest wagon. 

This is one of the main reasons why most of North America started driving on the right, compared to other British colonies. Being a much bigger country, hauling large wagons was essential for building cities.

So, the whole of North America eventually shifted to the right after independence. The first keep-right law in the US was passed in 1792 for the Philadelphia and Lancaster turnpike. Later, several other states followed suit including Massachusetts in 1821. Now, almost all the states excluding the Virgin Islands follow the right-hand traffic rule.

Unlike the US, several states in Canada continued driving on the left till the second world war came around. 

However, some special purpose vehicles like postal service trucks, garbage trucks, parking enforcement, and more have the driver’s seat on the right side for easier access and convenience.

Similarly, almost all French colonies drive on the right. Although Japan was not part of the colonization, they did involve the British to build railways, all of which drove on the left side, eventually leading to all traffic driving on the left.

Vehicle imports also played a significant role for some countries, and they started following the neighboring country’s driving styles. Unlike Japan, Korea currently drives on the right after it passed to American and Russian influence following the second world war. 

In North America, the Ford Model T was the first mass-produced vehicle with a left-positioned steering wheel. This eventually led to all other manufacturers following the same trend. Several countries like the UK have tried to shift to the right, but because of the significant costs involved, decided against it.

In some cases, where neighboring countries follow different traffic sides like in Africa and some parts of Asia, drivers will have to switch sides as soon as they enter the new country using simple traffic lights to enable the switch. 

The most recent traffic switch was done by Samoa in 2009, where the whole country shifted from RHD to LHD, mainly to allow cheaper importation of cars from neighboring countries like Australia, New Zealand, and Japan. Samoa is also the third country to make the switch. The country started driving on the right initially because it was a German colony, but after it gained independence in 1962, the government wanted to swap sides for economic reasons and cheaper imports. 

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