Cruise Control Hydroplane Warning

Outline

Email forward warns that drivers should not use cruise control in wet conditions because its use can cause the vehicle to accelerate and fly through the air if it hits standing water and hydroplanes.

Brief Analysis

The message contains some valid information, but is nevertheless misleading and alarmist. Using cruise control in wet conditions certainly can be dangerous but it will NOT cause your vehicle to speed up and fly through the air.

Example

Subject: Fw: Great safety tip

NEVER KNEW THIS BEFORE

I wonder how many people know about this?

A 36-year-old female had an accident several weeks ago and totalled her car. A resident of Wollongong, NSW, she was travelling between Wollongong & Sydney. It was raining, though not 
excessively, when her car suddenly began to hydroplane and literally flew through the 
air.

She was not seriously injured but very stunned at the sudden occurrence!

When she explained to the policeman what had happened, he told her something that every driver should know - NEVER DRIVE IN THE RAIN WITH YOUR CRUISE CONTROL ON. She had thought she was being cautious by setting the cruise control and maintaining a safe consistent speed in the rain. But the policeman told her that if the cruise control is on and your car begins to hydroplane -- when your tyres lose contact with the pavement, your car will accelerate to a higher rate of speed and you take off like an airplane. She told the policeman that was exactly what had 
occurred.

The policeman estimated her car was actually travelling through the air At 10 to 15 kms per hour faster than the speed set on the cruise control.

The policeman said this warning should be listed, on the driver's seat sun-visor - NEVER USE THE CRUISE CONTROL WHEN THE PAVEMENT IS WET OR ICY, along with the airbag warning. We tell our teenagers to set the cruise control and drive a safe speed - but we don't tell them to use the cruise control only when the road is dry.

The only person the accident victim found, who knew this (besides the policeman), was a man who had had a similar accident, totalled his car and sustained severe injuries. If you send this to 15 people and only one of them doesn't know about this, then it was all worth it. You might have saved a life.

Detailed Analysis

This email forward warns that drivers should not use cruise control in the rain. The message claims that using cruise control can actually cause the vehicle to accelerate through the air if it hits standing water and hydroplanes (aquaplanes).

While the core claim (don’t use cruise control in wet conditions) is valid, the message seriously mangles the facts and is therefore misleading and overly alarmist.

Certainly, using your vehicle’s cruise control in wet or icy conditions can be dangerous – but not for the reasons outlined in this warning message. It almost goes without saying that aquaplaning can occur regardless of whether cruise control is engaged or not. Aquaplaning occurs when a tyre’s grooves cannot remove water quickly enough and the tyre therefore loses contact with the road surface and skims across the top of the standing water. Car accidents often happen as a result of aquaplaning, but in many cases this is due to poorly maintained vehicles, driver inattention or poor road conditions and has nothing at all to do with cruise control.

That said, if cruise control is engaged when aquaplaning occurs, the driver’s subsequent reaction could make the encounter worse than it may have otherwise been. For example, the driver may hit the brake heavily to disengage cruise control and this could lock up the wheels completely. Furthermore, drivers often move their feet away from the pedals when cruise control is engaged and they may also be a little less attentive than normal. In an aquaplaning situation the small delay caused by these factors could equate to the difference between a safe recovery and a serious accident. Also, an inattentive driver could hit the accelerator instead of the brake to disengage cruise control, and this could of course speed up the vehicle and lead to loss of control.

However, the claim in the message that cruise control itself can actually make the vehicle accelerate and fly through the air in a hydroplaning situation is dubious at best. A CarPoint Australia article that debunks the claims in the email notes:

This is the key that makes a nonsense of the email. Modern cars take their speedo reading from the driveshaft or transmission. This means the cruise control bases its responses on the speed of the driven wheels, not the car itself. This is an important distinction and fail safe position.

If the driven wheels skid because they lose grip, the spinning wheels will cause the speedo to show a higher reading which will force the cruise control to release the throttle faster than most drivers. Regardless of whether the car itself slows down or speeds up, the cruise control will always reduce the throttle no matter what until the driven wheels slow down back to the pre-set speed.

If the wheels continue to slip under this scenario, this will always leave the car travelling more slowly relative to the road, not faster as described in the email.

 

This finding is confirmed by the RAA’s Technical Manager Mark Borlace, who explains:

“Should the car’s tyres break traction with the road, such as in an aquaplane situation, the increase in wheel speed would be sensed and the cruise control system would then reduce the amount of throttle and maintain the set speed.”

“Additionally, cruise control systems are deactivated as soon as the brake is applied. As braking is usually an automatic reaction in most emergency situations, the scenario of cruise control causing an increase in vehicle speed is highly unlikely.”

 

Thus, there is no inherent factor in the cruise control mechanism itself that could lead to a hydroplaning vehicle speeding up and flying through the air.

Like many email “warnings” there is no way of verifying if the event described in the message actually occurred or was simply added to drive home the core points. The version included here is set in Australia. However, other versions with virtually identical wording have featured US place names. Another popular version changes the location to a road between Gladewater & Kilgore, Texas. This duplication implies that, at least for later versions of the message, the perpetrator is not relating an actual incident he or she has experienced but has simply altered an existing message to fit local conditions.

The bottom line? Using cruise control in wet conditions certainly can be dangerous but it will NOT cause your vehicle to speed up and fly through the air. Engaging cruise control in any road situation that is less than optimal is ill-advised. Such road situations include not only wet and rainy conditions , but also icy roads, high traffic, poor visibility and rough, narrow, hilly or excessively bendy roads. However, do we really need an unverified and factually dubious email forward to make us aware of such factors? I would hope that not using cruise control in wet or other potentially dangerous conditions would simply be common sense for any responsible driver.