Engine and other automobile systems are increasingly controlled electronically. This has led to improved fuel economy, reduced pollution,  improved driving safety and reduced manufacturing costs. However the automobile  is a hostile environment : especially in the engine compartment, where high temperature, humidity, vibration, electrical interference and a fine cocktail of potentially corrosive pollutants are present. These hostile factors may cause electrical contacts to deteriorate, surface resistances to fall and sensitive electronic systems to fail in a variety of modes. Some of these failure modes will be benign, whereas others may be dangerous and cause accidents and endanger to human life.  The Annex to the IEE Guidance Document on EMC and Functional Safety lists 21 electronic systems that may be present in the modern automobile, some of which have the potential to  endanger the safety of the vehicle occupants or other road users should an error or a mis-operation occur. 

An electronic system frequently fitted to modern vehicles is a cruise control system, or vehicle speed control system, which keeps a vehicle's speed constant on long runs and therefore may help prevent driver fatigue. However, cruise control is not suitable for all road conditions and drivers are warned not to use it at low speeds, or in heavy traffic, on winding roads or in foggy or icy conditions. There are built-in logical interlocks intended  to prevent its use in certain gears, below certain speeds etc. and switches that disconnect the cruise control if, for example, the brakes are applied. 

If the driver hands over speed control to a cruise control system, then the capability of the system to control speed to the set value is just as critical to safety as is the capability of the driver to control speed manually. Yet, strangely, although the capability of the driver  is regarded as a critical safety factor - e.g. the slogan "Don't drink and drive" - not so cruise control systems which are currently classified as non-safety-critical. 

It is sometimes argued that should the cruise control system malfunction,  the driver can  intervene, either by applying the brakes or switching of the engine. But is this really so? Would it be wise to switch off the engine or apply the brakes in some situations? Surely, the manufacturers should be able to design in gentler means of bringing such potentially dangerous situations under control?