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Operating at the proper pace for all road conditions is the definition of proper speed management. This involves considering the state of the road, visibility, and the speed and flow of the traffic.


Speed and Stopping Distance


When stopping a car, four things must happen:


  • Perception distance — The perception distance is the time it takes for your brain to register a threat when you first see it. A motorist who is paying attention has a perception time of around 1/4 second. A car moves 60 feet in roughly 1/4 of a second at 55 mph.


  • Reaction distance — Reaction distance is the distance a car travels between the moment your brain instructs your foot to let off of the accelerator and the time your foot touches the brake. The typical driver has a 1/4-second response time. At 55 mph, it adds another third of a second and 60 more feet of distance.


  • Brake lag distance — When using air brakes, it takes about a half second for the mechanical action to occur.


  • Braking distance — The length of time it takes for a car to stop when the brakes are applied. The vehicle's weight, length, and speed as well as the state of the road have an impact on the stopping distance. The parts of a heavy vehicle, such as the brakes, tires, and springs, are made to function optimally when the vehicle is fully loaded. A big truck goes around 170 feet at 55 mph on dry pavement with decent brakes and can stop in about 5 seconds.


At 55 mph, it will take between 6 and 7 seconds to stop, and under ideal circumstances, the car will go around 290 feet (nearly the length of a football field) when you add together perception, response, brake lag, and braking time and distance. Higher speeds significantly lengthen the stopping distance.



Speed and Surface Conditions


To control a vehicle, traction is required. A vehicle has less traction the less resistance there is between the tires and the road. Lower speeds are required because of certain road conditions that limit traction.


Rain — Rain may have an impact on a car's traction. Oils on the road rise to the surface of the road when the rain starts to fall and combines with the oils there. There is a coating of slick oil between a car's tires and the road until fresh rain breaks down and washes these oils away. The duration of this illness ranges from a few minutes to a few hours.

When wet, new pavement is slicker than old pavement. The oils in the freshly laid pavement are more concentrated because they have not yet been removed by years of rain. Oil and water combining to form a white foam on the road is a sign that the surface is slick.


A car may hydroplane if there is standing water on the road due to heavy rain. A vehicle has a higher likelihood of hydroplaning the quicker it is moving through standing water. This is because traction can only exist when a vehicle's tires are in contact with the pavement. The tires lose traction if they are moving along a wall of water. On relatively little water, a tractor-trailer may hydroplane even when fully loaded.


Vehicle speeds should be decreased by at least 13 when it rains.


Snow — Snow impairs sight and reduces traction. For the sake of vision and vehicle control, you must slow down.


There are usually few issues when a light, powdery snowflake blows off the road. The road will develop a smooth, slick surface if there is enough powder to cover it. Vehicle handling may be impacted by heavier, slushier snowfall. Snow that has been compacted too tightly may turn icy.


In snowy circumstances, vehicle speeds should be reduced by at least half. Remember that you must be certain that you can stop and maneuver safely given the road conditions while choosing your vehicle's speed in snowy conditions.


Ice — A road that is ice might be riskier than one that is covered with snow. The possibility of black ice must be considered by drivers when the temperature is close to freezing.


When temperatures drop quickly, moisture on the road freezes into a smooth, practically invisible, slick surface, which is known as black ice. Black ice conditions give the impression that the road is moist when it is frozen.


A motorist might feel the front of the car's mirrors or antennae to check for ice buildup. Ice is also developing on the road if it is forming there. The driver should keep an eye out for debris from other cars. Ice could be developing if the spray stops.


The state of the roads will determine a driver's behavior. In ice conditions, a motorist should at the very least reduce their speed by half. When choosing your vehicle's speed, just as in snowy circumstances, you must be certain that you can stop and maneuver safely given the road's conditions. The motorist should off the road as soon as it is safe to do so if the going is exceedingly slick.


Even after the ice on the sunny parts of the road has melted and the pavement is dry, shady sections of the road might continue to be slick. On roads with shade, go more slowly.


Bridges may ice before roads do as the temperature lowers. Avoid making any adjustments to your driving style when crossing the bridge if slick conditions are anticipated. Keep your speed smooth and constant.


Speed & road shape


Curves — Recall that stated speed limits on bends are made with automobiles in mind. A car may slide off the road or flip over if the driver enters a curve too quickly (at or above the legal speed limit).

Before a bend, reduce speed to a safe level that is at least 5 mph slower than the official limit. As necessary, reduce your speed, but be careful while braking since doing so might be hazardous. It is simpler to lock the wheels of your car and induce a skid. In a bend, never go above the stated speed limit. Additionally, be in a gear that will allow you to gradually accelerate into the curve. You can keep control of your car by doing this.

Grades —When navigating upgrades and downgrades, speed management is influenced by vehicle weight and gravity.


Your vehicle needs to exert more effort to sustain speed and defy gravity on an upgrade. You must push harder on the accelerator or even downshift to a lower gear to maintain pace.


Your car accelerates more quickly on a descent because it is using gravity to its advantage. The weight of the vehicle affects the speed of trucks descending a gradient. Greater acceleration is desired by heavier vehicles over smaller ones. Maintaining a safe and uniform pace requires caution.


Speed and Visibility


You need to always be able to stop while staying in your line of sight. In other words, you need to be able to stop within what you can see in front of you. You must slow down while driving at night or in bad weather (rain, fog, snow, etc.) so you can stop your car in your line of sight.


Speed and Traffic Flow


The safest place to drive while there is heavy traffic is often the speed of the other cars on the road, assuming you can keep a safe following distance and you are not exceeding the official speed limit. If you can't maintain a safe following distance, reduce your speed to 3–4 mph below the rate of traffic.


Drivers often think that going above the speed limit will help them gain (or lose) time. This isn't always the case while driving in traffic. If you are moving more quickly than other vehicles, you will have to pass other vehicles. Your likelihood of getting injured in an accident rises as a result. Your degree of weariness may grow as a result of this sort of driving, increasing your likelihood of an accident.


It is best to go with the flow of traffic when safe and legal to do so.



Obeying the Speed Limit


Part of the foundation for speed limitations is excellent speed control. They take into consideration many factors, including traffic volume, road conditions, and sight distance restrictions. There are several good reasons not to speed. This section lists a few of these causes.


Accidents — At faster speeds, accidents are more likely to happen. You can't handle your car as well since there is less time for response. Additionally, research suggests that the likelihood of deaths increases with the speed at which the collision happens.


Penalties — If you have two or more convictions for exceeding the legal speed limit (15 mph or more) in either a commercial or non-commercial vehicle, operating a commercial motor vehicle is forbidden (including your car). The Federal Motor Carrier Safety Regulations (FMCSRs), Section 383.51, state that excessive speeding offenses may result in a suspension of 60 to 120 days.


Any convictions for speeding, regardless of whether they result in disqualification, are permanently recorded on your driving record. Your employer is required to check your driving history at least once a year and if you start working for a new motor carrier.


Convictions for speeding may also be expensive. Speeding offenses may result in fines as well as increased insurance rates if your insurance provider keeps note of them.


Maintenance costs — Increased speeds might affect maintenance costs. Brakes and tires degrade more rapidly at higher speeds. As speed increases, overall wear also does.


Fuel economy —Your speed directly and significantly affects how efficient you are with fuel. These vehicles were never meant to be racers. You will have achieved success if you can get six miles per gallon. By lowering your speed, even by a few miles per hour, you may increase your fuel efficiency and save hundreds of dollars over a year. Think about this. How much money control you saved if your gas mileage is six miles per gallon at 60 mph and five miles per gallon at 70 mph? If you travel 130,000 miles a year and the average price of petrol is $2.85 per gallon, you have saved about $12,000 only on gas. Is it advantageous to go a little more slowly?


Why do drivers speed? — Reducing the distance traveled and/or making up for lost time are two of the main reasons tractor-trailer drivers accelerate. There is little time gained by speeding, according to research.


Avoid the temptation to speed by planning ahead and making the best use of your time as possible.




You learned about the variables involved in halting a tractor-trailer and the role speed plays in safe operation in this chapter.

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