It's a lesson that most of us learn years before were old enough to drive: Red means stop, green means go. Simple enough. But what happens when you live in a culture where green also means blue?

Drive around Japan long enough and you'll find “go” signals in different kinds of blue. “Is this signal broken?” you might ponder. “Did some careless workers install the wrong bulbs?” The answer, as Atlas Obscura points out, is not in the wiring, but in the Japanese language.

Hundreds of years ago, the Japanese language included words for only four basic colours: black, white, red, and blue. If you wanted to describe something green, you'd use the word for blue-ao. That system worked well until the word midori began showing up to describe green. Even then, midori was considered a shade of ao. This sudden switch-over had lasting effects in Japan.

Today you'll still see green things doubtfully labelled blue. A fruit seller might sell you an ao-ringo (blue apple) only to disappoint you that it's actually green. Likewise, green bamboos are called aodake (“blue bamboos”) and an inexperienced employee may be called aonisai, meaning a “blue two-year-old”. And that brings us to traffic lights.

Initially, Japan's traffic lights were green as green can be. Despite this, the country's official traffic documents still referred to them as ao. International traffic law commands all “go” signals must be represented by green lights, and Japanese linguists objected to their government's decision to continue using the word ao to describe what was clearly midori. The government decided to compromise. In 1973, the government passed through an order that traffic lights use the bluest shade of green possible-still technically green, but noticeably blue enough to justifiably continue using ao nomenclature (命名法).

So, while it may appear that Japan uses blue traffic lights, the government assures us it's actually just a very blue shade of green-green enough to satisfy international regulations blue enough to still be called ao. Don't ever say the government never solved anything.

Driving a car is not just handing controls and judging speed and distance. It requires you to predict what other road users will do and get ready to react to something unexpected. When alcohol is consumed, it enters your bloodstream and acts as a depressant (抑制药), damaging eyesight, judgment and co-ordination (协调), slowing down reaction time and greatly increasing the risk of accidents. Even below the drink driving link, driving will be affected.

Alcohol may take a few minutes to be absorbed into the bloodstream and start action on the brain. Absorption rate is increased when drinking on an empty stomach or when consuming drinks mixed with fruit juice. To get rid of alcohol from the body is a very slow process and it is not possible to speed it up with any measures like taking a shower or having a cup of tea or coffee.

The present Road Traffic Ordinance states clearly that the limit of alcohol concentration is:

●50 milligrams of alcohol per 100ml of blood; or

●22 micrograms of alcohol per 100ml of breath; or

●67 milligrams of alcohol per 100ml of urine (尿液).

Drivers who cause traffic accidents, or who commit a moving traffic offence or are being suspected of drink driving will be tested.

Any driver found drinking beyond the limit will be charged. The driver declared guilty may be fined a maximum of HK $25,000 and be sentenced to up to 3 years in prison and punished for 10 driving-offence points; or temporarily banned from driving.

The same punishment applies to failing to provide specimens (样本) for breath, blood or urine tests without good excuse.

Drink driving is a criminal offence (违法犯罪行为). Be a responsible driver, think before you drink. For the safety of yourself and other road users, never drive after consuming alcohol.

The first traffic lights in the United States were installed (安装) because of an increase in traveller on the road in the 1920s. Worried about accidents, towns and cities built traffic towers to help the flow of cars. Officers manned the towers, using whistles and red, green and yellow lights to indicate to drivers when they should stop and go.

Due to the absence of effective traffic signal systems on some streets, it caused risks at corssroads. Then, William Potts created the first tricolour, four-directional traffic signal. The very first four-directional traffic light was installed at Woodward Avenue and Fort. But throughout the country, there were still a lot of systems for traffic lights and patterns in place. Since this could end up causing more problems for drivers, the Federal Highway Administration set uniform standards in 1935 for all road signs, pavement markings and traffic signals, requiring them to all use red, yellow and green light indicators.

Red is the colour with the longest wavelength, which means that as it travels through air molecules, it gets diffused (扩散) less than other colour, so it can be seen from a greater distance. Yellow has a shorter wavelength than red but a longer wavelength than green. This means that red is visible the furthest away, yellow in the middle and green the least distance away — a helpful advanced warning for needing to slow or stop. But this could be a coincidence. Red meaning stop originated with train warning lights, and it’s not clear whether that was chosen based on wavelength, contrast against green nature or natural association of red with things like blood. It could be a combination of all three!

Back in the 1900s, some stop signs were yellow because it was too hard to see a red sign in a poorly lit area. Eventually, highly reflective materials were developed, and red stop signs were born. Since yellow can be seen well at all times of the day, school zones, some traffic signs and school buses continue to be painted the colour.