We usually read text looking straight at it. If you pick up a magazine or read a screen it is more-or-less at a 90-degree angle to your eye-line. However, sometimes a designer knows readers will look from another angle. The lettering has to look right from this viewpoint with anamorphosis [topic 1].
The lettering ‘SLOW ARAF’ ‘BUS’ or ‘STOP’ written on roads is an example of anamorphic design. The letters are very tall so that you can read them at an oblique angle from far down the road in a car. If the car is going fast, the driver needs to read the warning from further away.
The Government has rules about road lettering. The typeface is called ‘Transport Medium’. The letters have a standard width, for example an A is 544mm wide and an F is 476mm wide.
Without distortion the letters are 560mm high. For roads with a speed limit of 40 miles an hour or lower they are stretched to 1,600mm high. For roads with a speed limit over 40 miles an hour they are stretched to 2,800mm high. In this case the height of the letter is multiplied by 5.
Another example of distortion of lettering are the adverts on sports pitches. They are stretched to look right from the position of the television cameras.