At road junctions such as crossroads and roundabouts traffic lights are commonly used to indicate which direction traffic can travel in at any one time. This reduces the likelihood of accidents and ensures that cars moving in each direction have the opportunity to pass through the junction.

The task of changing the colour shown at each set of lights to ensure that cars can only travel in one direction at a time is carried out by a computerised control system. The control system will let traffic move in each direction in turn.

There may be sensors in the road or on the lights that detect how many cars are passing in each direction. The amount of time that each light is on red or green for could be adjusted so that if more cars are travelling in one direction than another they get more time to go through the junction.

At quiet times of day the lights at a junction may be set to stay on green in one direction all of the time. Sensors will detect if any vehicles arrive at the lights from the other directions. If this happens the lights will change to let them pass.

The operation of the traffic lights at different junctions can be co-ordinated to ensure that cars do not get stopped too many times. Here is an example of two sets of traffic lights at crossroads on one road :

Most traffic travels along this road in the direction indicated by the red arrow. If cars travel at around the speed limit then the operation of the two set of traffic lights will be co-ordinated so that when cars that passed through set A on green arrive at set B, the lights at this junction will also be on green to let them through.

In a real system the operation of many sets of traffic lights can be co-ordinated. By co-ordinating the operation of traffic lights throughout a town it is possible to reduce journey times for drivers.

The traffic lights are able to communicate with each other using wireless (radio) network connections. Information collected by sensors at the traffic lights may also be sent to a central monitoring station so that the people in charge of managing the traffic can spot busy routes and traffic jams. A central computer system may be able to adjust the timing of the various sets of lights so that if a traffic jam is building up the traffic in the busy area is given priority at the lights.

When a car enters an area covered by congestion charging a digital camera photographs it and sophisticated software reads the car registration from the number plate. This is looked up in a database so that the owner of the car can be identified. Other cameras will monitor the route that the car follows so that its entire journey is known. The car owner will then be charged for the journey. It may be possible to pay for the journey over the Internet by using online banking.

The cost of a journey will depend upon the route followed and the time of day. By charging more at busy times it is possible to persuade some drivers to travel at other times or use public transport instead.

Magnetic sensors in the road detect when a car approaches an entry barrier. If there are spaces in the car park then a ticket will be printed for the driver to take and the barrier will be lifted. The ticket will have the time of arrival printed on it in human readable form and possibly also in machine readable form such as a barcode. When a driver leaves the car park a charge is made based on how long her car has been parked. This money may be collected by a person or by a machine that reads the barcode from the ticket and uses the data stored in the barcode to calculate how long the car has been parked for.

Sensors on the exit roads will count how many cars leave the car park. By counting the number of cars arriving and leaving a computer can calculate how many spaces are free. If the car park is full then a warning sign near the entrance will indicate this and cars that arrive at the car park will not be allowed to enter.

If there are several car parks in a town then signs can be placed on roads going into the town to indicate how many spaces are available in each car park. This will avoid the problem of people going to full car parks as they will be able to see a car park is full and choose an alternative less busy one to go to.

At the end of each day the computerised system will be able to calculate the total amount of money that has been taken at a car park.

The receiver receives signals from a network of satellites called Global Positioning Satellites (GPS). From these the computer system can work out the location of the car. Maps are stored on a CD or DVD and based on the position of the car the computer can load the correct map and display it on the monitor with the car's position indicated.

Before setting out on a journey the driver can enter the name or postcode of the place that he is travelling to. The computer can locate the destination on the map and work out the best route for the driver to take. As the journey progresses the monitor will be used to indicate when the driver should turn onto another road. Directions may also be announced through speakers using speech synthesis so that the driver does not have to take his eyes off the road.

A satellite navigation system may also be linked to a traffic information system which can receive information about traffic jams and roadworks by radio. If a road involved in a journey is busy the computer system will be able to automatically change the recommended route to minimise the delay.