Here's me on day one, the car still in the parking lot, looking a little terrified at

the prospect of driving.

Not because I was tired, or because I hate driving.

It was because in Australia, you drive on the left side of the road,

whereas in the US, you drive on the right.

Most countries in the world — about two-thirds — drive on the right side.

Which leaves one third that drives on the left.

You might be wondering why people who drive on the left don't just switch over to the right.

The thing is, left-hand side traffic was the worldwide norm for a long time.

So how come a split now exists?

Well, the reason boils down to two main factors:

One, the fact that most people are right-handed.

And two, the fact that countries were using different forms of transportation at the time

formalised road rules began to emerge.

Back in the middle ages — way before cars existed — people mainly travelled around on horseback

or by foot.

People kept to the left so they could keep their dominant hand closer to the centre of the road.

Remember this was a time when people often carried weapons on them — such as swords,

knives or daggers — while travelling because of bandits and outlaws.

Also, people almost always mount horses from the left side — and it's safer to mount

from the roadside than in the middle of the road.

This left-side travelling continued for years across the world until about the time of the

French Revolution.

There was a big class distinction on the roads of France at the time — the wealthy would

drive their carriages on the left and force poorer people to travel to the right.

But by the end of the revolution, the aristocracy began travelling on the right to blend in

with the lower classes, and France's roads effectively became right-side travel.

So you had France travelling on the right, and places like England travelling on the left.

Throughout Britain it was more a matter of custom than widespread regulation until 1835,

when parliament passed a law forcing traffic to keep left.

In France, the keep-right rule was established more firmly by this guy.

As Napoleon conquered countries across Europe, those countries were forced to switched sides.

Meanwhile in the US, one particular wagon was a big driving force for keeping to the right.

The Conestoga wagon became popular in the late 1700s, as a way to transport heavy goods.

These massive wagons could hold thousands of kilograms worth of cargo, and needed teams

of horses to pull them along.

There was no driver's seat, so the driver would usually sit on the rear left horse — so

they could still hold a whip in their right hand.

Because of this, the wagons travelled on the right, so the driver — sitting on the left

— would have more visibility over the rest of the road.

In 1792, Pennsylvania officially passed the first keep-right law in the US, to this turnpike.

Twelve years later, New York enforced right-hand travel on all public highways, and it slowly

spread across the rest of the US.

In time, more and more countries shifted to the right.

As they found themselves surrounded by converted land neighbours, it was just easier to follow suit.

When the US started putting steering wheels on the left, that became extra incentive to switch.

Cars initially had the wheel on the right, following horse-drawn buggies.

Ford was the first to put the wheel on the left with the Model T in 1908.

Initially, it was just to make disembarking easier.

But car manufacturers soon realised it was better — and safer — for the driver to

sit more towards the centre of the road.

And because the US is such a big car exporting country, this was an extra push for more countries

to switch over to the right, so they could use the cars.

Obviously not everyone made the switch.

British colonies remained on the left, and still do for the most part.

And other countries like Japan and Thailand, which were never British colonies but had

dealings with the British, have also kept to the left.

But most countries switched to the right in the early to mid 20th century.

In fact, only three places have switched back from right to left in recent times.

In Japan, Okinawa was controlled by the US after WWII and made to drive on the right.

It switched back to the left on July 30, 1978, after being returned to Japan 6 years previously.

Timor-Leste switched to the left under Indonesian rule in 1975.

And Samoa switched over in 2009, so they could import old Australian cars

instead of more expensive US cars.

The Samoans had a smooth changeover — they got a two-day national holiday to ease traffic,

and a three-day ban on alcohol sales to deter accidents.

But they had a relatively small population at the time of about 180,000 people.

So what would happen in a country with a lot more people

— and a lot more that could go wrong?

Sweden switched from left to right in 1967.

With a population of about 7.8 million people at the time,

there was a lot to prepare for H-Day.

Road markings had to be repainted, bus stops relocated, intersections and one-way streets redesigned,

and about 360,000 street signs changed.

At precisely 5am on September 3, Swedes were directed to switch over to the right.

The whole process cost 628 million kronor — the equivalent of more than $400 million today.

But the country's road networks and infrastructure a lot more sophisticated now than they

were 50 years ago — not to mention there are a lot more people and cars.

A switch nowadays would be a lot harder and cost a lot more.

It's the main reason why we won't see another country switching sides any time soon —

it would be a huge logistical exercise that would cost a lot more than people

are willing to spend for something that isn't needed.

If it ain't broke, don't fix it.

In the end, it only took a day or two for us to be comfortable driving on the other

side of the road — and it's probably what travellers will have to keep doing.

You may have noticed that most left-side driving countries are actually

islands, which helps justify not switching over.

For the few that do share borders with right-side driving countries, most of the time it's

a non-issue - you'd have to go through customs first, so you'd go through border security

on one side and exit out the other.

But for a few countries, they've come up with some inventive solutions.