General Technical Documents

Concerns Regarding Aquaplaning and the use of Cruise Controls

There has been concern raised in the press regarding “loss of control” of a vehicle whilst using cruise control during heavy rain. The concern being that if a vehicle using cruise control starts to hydroplane then the cruise control will “accelerate” the vehicle and because of the hydroplaning of one or more tyres cause the vehicle to skid “under power” possibly causing a collision.

The term hydroplaning is commonly used to refer to the skidding or sliding of one or more of a cars tyres across a wet surface. Hydroplaning occurs when a tyre encounters more water than it can scatter. Water pressure in the front of the wheel pushes water under the tyre, and the tyre is then separated from the road surface by a thin film of water and loses traction. The result is loss of steering, braking and power control.

In normal circumstances the tread patterns and grooves on the tyres can dissipate the surface water that they encounter ensuring that the rubber of tyre remains in contact with the road surface however if there is a lot of water on the surface combined with the vehicle travelling at speed or the road surface has been dry for some time and now has fresh water on it, (which will mix with the surface oils), then the contact between the tyre rubber and the surface can be lost and control of the vehicle will be reduced.

The normal effect of hydroplaning is that the vehicle speeds up for a few seconds because of the reduced friction with the road surface but then slows down as a result of the fact that power is no longer being transmitted to the road surface; the slowing of the vehicle in most cases causes the combined effect of the tyre tread and the weight of the vehicle, (a vector force perpendicular to the road surface), to cut through the surface film and re-establish contact between the road and the tyre.

With modern tyre designs hydroplaning is a lot less frequent than it used to be though surface water on the road is always something that a careful driver needs to be aware of. Heavy rainfall should always cause a driver to reduce their speed to one where hydroplaning is less likely.

The concern raised in the media is that using a cruise control is dangerous because it continues to apply power to the driven tyres despite the fact that they have lost contact with the road surface, this was true of “old” cruise control designs however newer vehicles fitted with cruise control will all cut the cruise control off if wheel slip is detected which is what would happen if the vehicle started to hydroplane. Notwithstanding this, cruise controls are a driver aid and the driver should remain alert and aware of the road conditions around their vehicle even if cruise control or active cruise controls are being used. In the event of a sudden downpour it would be sensible to reduce speed in any case and in so doing stop using the cruise control until it is safe to do so again.

The media indicated that cruise control should only be used on dry roads however this is no longer necessary though cruise controls should be seen as the driver aid that they are and used with care as with all driver aids.

Associate Process Flow Chart

The following attachment is a flow chart that details the progress and steps that will be followed by the average Associate on joining IAM RoadSmart with intention of becoming an Advanced Driver. The sequence may look a little onerous on paper however is simple and functional ensuring that all Associates get to being “Test Ready” at the earliest opportunity and with the best possible likelihood of getting a good pass in the test. (If you are an Associate reading this and need clarification of any of the details on the chart then speak with your Observer who should be able to answer all of your questions).

Associate Progress Flow Chart v4 2.3.2017

A Chart of Useful Acronyms used by IAM RoadSmart Members

The following sheet shows some of the more common acronyms and aide memoire used by members of IAM RoadSmart. This is by no means an exhaustive list but may help in remembering some of the basic advanced driving skills.

Acronyms v3 2.3.2017

This page contains a variety of documents relating to various aspects of advanced driving and safer driving. If you have any thoughts about what should appear here then please let us know. This is intended to be a resource regarding technical aspects of driving today.

First published as a technical item in our Group Newsletter, repeated here as it has general informative appeal.

Forward and Rear Cameras – a Technical Advantage


Published in our Newsletter but worth repeating here.