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Truck Driving Safety Expert Witness:
Left Foot Braking Increases Safety

Written by Don Asa in 2011

Trucking Expert Witness Articles


Reaction time and perception time are two critical components of driving and surviving as a professional driver. In this article, I will address how to effectively reduce reaction time and improve perception time. An average perception time is .75 seconds, and an average reaction time is also .75 seconds.

Imagine you are driving and see a potential problem ahead of your vehicle. For example, a truck in the emergency lane, a strong wind condition, an on-ramp with cars entering, or just brake lights on a vehicle in the number one lane –in short any type of scenario which might cause you to have to slow your speed or come to a stop.

Placing your foot on the brake is an appropriate reaction at this point. After having perceived the potential situation, it then takes a simple message fired from the brain to the foot telling it to press the brake pedal.

Think about this short series of events. As a professional driver, when traveling 55 miles per hour, you are moving 80 feet per second.  If you perceive the problem early enough, it’s possible to brake as much as 60 feet before other drivers begin their braking.

By using left foot braking and essentially eliminating the ¾ second reaction time, the driver gains a 60-foot advantage over other drivers. 60 feet is roughly the same as the length of the entire truck! By heightening your perception, you’ve given yourself far more control over the vehicle. The equipment isn’t creating momentum during your normal reaction time –for the ¾ of a second when you have no braking, and that tiny increment of time can make all the difference to the problem you’re facing.

With articulated vehicles (any vehicle with one or more hinges, such as a semi or a set of doubles) the driver must factor in balance. Balance begins with understanding the hinge, such as the fifth-wheel. It’s called a hinge because it can swing left or right of center just like a door hinge. So, considering how to keep the hinge straight when braking is important to any braking scenario. Different pressure on one side or the other of a hinge can cause the towed vehicle to swing either direction. 

This principle is generally irrelevant on dry pavement; however it is pertinent when driving on slick pavement. In a slick pavement scenario, when the driver does nothing except take their foot off the throttle, pressure develops on one side of the hinge, different from the pressure on the other side of the hinge. The pressure on the front side of the hinge comes from compression of the engine activating pressure back down through the drive train. The pressure on the backside of the hinge comes from the trailer’s weight pushing. Assuming the trailer weighs 60,000 pounds (load and equipment) and the tractor weighs 17,000 pounds, it’s obvious who is going to win the argument.  This can of course be aggravated by the driver’s steering input. 

A skilled and competent driver is always thinking about balance and control and making sure to exercise the correct options. So, how to keep the balance?  The answer is, left foot braking. Braking with the left foot before your foot comes off the throttle, means that the tractor and the trailer both have braking ability and therefore equalized pressure on each side of the hinge.

Left foot braking is a useful skill for situations where your semi may be passed, such as on freeways, interstates, or any multi-lane situations. The vehicle passing always comes up in your mirrors and so you have the time to observe the vehicle, anticipate its speed (how many feet per second it is moving.) However, what you cannot do is read the driver’s mind. You can only observe that the driver is faster than your speed. The driver may very well swing into your lane and put you into the position of following too close and having to reduce your speed. 

The professional driver anticipates these possibilities and always has left foot on the brake pedal as other vehicles are passing. In this example, left foot braking can save two seconds in time, which at highway speeds of roughly 70 miles per hour, can amount to approximately 210 feet, which is a long way.

The only way a truck has a problem on slick ground is for the driver to do something radically different, like jump on the throttle, jump on the brakes in a radical way, or input steering into the machine while the trailer is pushing without any retarding or pulling effect. Remember to stay smooth, brake with your left foot, and you will eliminate a great many problems.

Rules for the Road:

Know What’s Ahead – Always pay attention to what is coming up on the visual horizon.    

Know What’s Around You – Anticipating what other drivers could do will help you navigate your reaction.

Beware of Your Load – When the trailer load is heavy, the pressure on the hinge is different. Plan accordingly for this situation.

Steady as She Goes – Maintaining your truck’s balance in all scenarios is critical to a safe ride. No matter the circumstances, no matter the traffic scenario, avoid surprise movements and employ left foot braking to protect yourself and others.

Don’t Trade Time for Safety – Lots of accidents develop over a few seconds of time.

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