What is a head up display (HUD)?

A head-up display, or HUD, is a system that projects information into the driver's line of sight without them having to take their eyes off the road.

Early systems only displayed data in a single colour, but the latest versions have full colour displays, enabling them to give clear sat-nav directions, and to make warnings more distinctive.

What information does a head-up display show?

Your speed is usually the largest piece of information on your head-up display, shown as a precise number.

In cars fitted with cameras that can reads speed limit signs, you'll often see the limit for the road that you;re on displayed.

If your car has sat-nav, then it's normal for directions to be displayed on the head-up display. Typically, they won't appear when you're just following a road, but will be displayed when you're approaching a junction or exit that you've got to take.

The images are usually extremely simple: a single arrow, or an outline of a roundabout, so that it can be understood in an instant.

Some systems, such as those used by BMW also include some entertainment functions into the head-up display. It will display radio stations or your song list as you scroll through them using a button on your steering wheel.

What types of head up display are there?

There are two main types of HUD system. The cheapest and most common has a small screen that rises from the dashboard ahead of the driver onto which the information is projected. The driver can adjust its position to suit.

This pop-up solution is not particularly attractive or sophisticated but is effective. It's an option on Minis and the Mazda 3.

The second type of display is much neater: the information is beamed straight onto the windscreen from a small module on top of the dashboard, behind the speedometer.

As well as looking less clunky, the idea of this integrated system is to give the impression of the information being displayed a few metres ahead of the vehicle. This helps the driver refocus their eyes from farther down the road to the HUD information, and back again as quickly as possible.

To cause them the least distraction, the driver can fine-tune precisely where on the windscreen the image is displayed.

What cars have a head up display?

A surprisingly large number, although few manufacturers fit the equipment as standard.

You can opt for a pop-up head-up display on much of the Mini range, including the Mini Hatchback and Clubman.

The Mazda 3 also offers the option of a head-up display.

Integrated systems are commonly found on more expensive cars, such as BMWs, Mercedes and Jaguars, although only as standard on high specification versions. For example, as an option on the BMW 318i SE, it costs £825.