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Advanced Cruise Control and road safety: good information needed

ACC can increase driving comfort as well as road safety. However, when used incorrectly it can lead to greater unsafety. It is also essential to provide information about when ACC should be used, and when not.

 

This became clear from a literature study that was based on the results of various Dutch and foreign projects. The projects studied mainly used driving simulator experiments, computer simulations of traffic flows, and, to a limited extent, field tests with cars fitted out with instruments. ACC has only recently been for sale, so that practical user information was either not or hardly available.

 

ACC

A sustainably safe road traffic requires sustainably-safe vehicles, as well as a sustainably-safe infrastructure. The Sustainably Safe vision emphasizes understanding of the human driver with all his/her capacities, limitations, and motivations. For a long time now, traffic and transport experts see an important role for intelligent transport systems when creating a sustainably safe road traffic. This includes the Advanced Driver Assistance Systems (ADAS) that support the driver's driving task and thus increases the driving comfort. An important development in this is the Advanced Cruise Control (ACC). It is also often called the Adaptive Cruise Control and Intelligent Cruise Control. ACC, an initiative of the motor industry, works as follows: If there is no vehicle directly in front of the ACC vehicle, the system maintains the intended speed set by the driver, consistent with the conventional cruise control. When a vehicle in front is detected, the ACC vehicle's speed is adjusted until again the distance equals that set by the driver. If the vehicle in front disappears, the ACC vehicle accelerates to the above-mentioned intended speed. SWOV's literature study showed that using ACC has advantages and disadvantages.

 

Advantages

The presently available ACC systems can have a positive road safety effect if they are used on motorways, outside the rush hours, and with good visibility weather. An advantage of ACC is that by increasing the user's comfort, he/she becomes less tired.

ACC also has a moderating effect on the speed, and the percentage of very short headway times gets smaller. An additional positive effect is that the fuel consumption drops. Moreover, learning to drive with ACC is easy, and the system is easy to use.

 

Disadvantages

As well as advantages, the existing ACC systems also have a number of disadvantages.

Using ACC on winding, urban provincial roads and on congested motorways is not desirable because, under these circumstances, the safety actually decreases. Vehicles in front, by going round a bend, can disappear from view, thus preventing the system from functioning properly. In addition, ACC drivers seem to accept smaller distances between themselves and oncoming vehicles while overtaking. They also seem to react later to traffic on the right that has priority when approaching an intersection. ACC should also not be used in traffic situations or in weather with a poor visibility.

For road safety reasons SWOV advises against using ACC in busy traffic, when there is congestion. ACC drivers have the inclination to drive faster than desirable in such situations. The ACC system is switched off because the driver has to brake more often himself. A simultaneous increase in road capacity and road safety is, therefore, not feasible with the current ACC systems.

It is worrying that the driver does not always react adequately in critical situations, or that the ACC system fails. To compensate for the negative effects of diminished alertness, ACC should, for example, be able to detect stationary vehicles.

 

The future

The road user must be well informed about when it is safe to use ACC and when it is not. SWOV advises good information, and sees driving lessons as one of the ways to provide such information. Other information agencies could inform road users about the safe use of ACC. The information should also emphasize the fact that the driver should regularly control the ACC system that it is still working properly.

 

The report 'Advanced Cruise Control and road safety; a literature study' (R-2003-24) [in Dutch with an English Summary]; can be consulted and downloaded on the SWOV website under Publications.

SWOV Research Activities 24 - December 2003

Knowledge base