Safe Speed For Semi Trucks

Safe Speed Is Important For Semis On The Road

June 21, 2018

Semis driving on North Dakota highways often travel fully loaded at 80,000 pounds, with some semis being allowed to travel on state highways at 105,500 pounds. Compare that to the weight of the vehicles you and I drive on the road every day, and any car or pickup that any of us are in does not stand a chance in a crash with a semi. For instance, the Ram 1500 quad-cab pickup I drive is likely around 5,500 pounds, and my wife’s Jeep is around 4,500 pounds. This is why it is so important that semis regulate their speed to allow for stopping to avoid issues that arise on the road.

Let’s Recap A Prior Blog

You may recall a previous blog titled Trucking Accidents: Know the rules for trucks driving in North Dakota weather, which discussed semi drivers having to use “extreme caution” in the operation of their semis in hazardous conditions such as snow, ice, sleet, fog, mist, rain, dust, or smoke, that adversely affect visibility or traction. The Code of Federal Regulations (CFR) 49 CFR §392.14 goes on to discuss reductions of speed by semi drivers when there are hazardous conditions.

Let’s recap some specific guidelines used in the North Dakota CDL Manual. Section 2.6.2 talks about guidelines or rules for semi drivers facing slippery conditions. Specifically, the manual discusses the following reductions in speed, as stopping distances are affected:

Types Of Slippery Surfaces

  • Wet Road Conditions: Semi drivers are to slow down by one-third. As such, if they are traveling at 55 mph, the manual suggests slowing to 35 mph
  • Packed Snow: Semi drivers are to slow down by one-half of their traveling speed. An example would be dropping from 60 mph to 30 mph
  • Ice: Semi drivers are to reduce speed to a crawl, and stop driving as soon as they safely can do so.

Stopping Distances

The North Dakota CDL Manual section 2.6.1 discusses stopping distance. As is discussed fully in the manual, there are three things to take into consideration for how long it takes any driver to stop a vehicle (including a semi): (1) perception, (2) reaction, and (3) braking distance. Let’s take those in turn.


It takes time for our brains to recognize something is going on. This is called perception time. From the time our eyes see brake lights coming on ahead, it takes time for our brains to perceive or recognize what we are seeing. This perception time under ideal conditions (sunshiny day, dry roads, great visibility, etc.) for alert drivers (fully rested, paying attention, no distraction, etc.) is 1 ¾ second. At 55 miles per hour, a vehicle will travel 142 feet before the brain has even recognized something is going on.


After our brain has recognized something, it now takes time to physically react to what is going on. This is called reaction time, and under ideal conditions, the reaction time for an average driver is ¾ to 1 second. If a vehicle is traveling at 55 mph, that means that before a driver can react to the hazard, the vehicle will have traveled another 60-80 feet.

Braking Distance

Semis take longer to stop than cars and pickups. The manual discusses the time it takes (after perception and then reaction) for a semi to stop at 55 mph on dry pavement with good brakes, which is about 216 feet.

Total those all up for a semi traveling 55 mph in ideal conditions with an alert driver, and here is what you have for a stopping distance: (perception) 142 feet + (reaction-lesser of the two) 60 feet + (braking distance) 216 feet=418 feet. So under the very best conditions with the most ideal/alert driver, it takes well over a football field (including end zones) to stop, nearly 140 yards. This is why speed is an important factor for drivers to consider.

The Importance Of Speed

The North Dakota CDL Manual section 2.6 states “Driving too fast is a major cause of fatal crashes.” Section 2.6.1 goes on to discuss how speed affects stopping distances and the force of an impact in a crash. Consider the table below:

Braking Distances

As you can see, speed in a crash could be the difference between surviving an accident with minor injuries and being killed.

How Weight Affects Stopping Distance

Let’s try an exercise, before you read the answer below, answer in your mind the following question:

If a semi is loaded at 60,000 pounds, and another at 80,000 pounds, which one stops first traveling at 55 mph?

I’m sure a great majority of you answered the semi weighing 80,000 pounds took longer to stop in that scenario. That makes sense but is wrong.

The North Dakota CDL Manual section 2.6.1 states that the brakes, tires, springs, and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Therefore, empty semis require greater stopping distances because an empty vehicle has less traction.

But let’s not get confused. That does not mean that more weight is better because more weight means more catastrophic force in many instances as well. The lesson to learn is that weight is something that should also be taken into account by a semi driver when making sure to drive for the conditions at hand.


I am a huge supporter of semi travel, as it greatly helps our economy and allows me and my family to get the things we need (or want) in our day to day life. However, it is very important that semi drivers understand the importance of driving safely for all conditions, as they are driving a machine that can become a weapon of mass destruction in the blink of an eye. I hope for any semi drivers reading this blog article, that they take to heart that I appreciate all of their hard work, long hours, and time away from their families. But I also ask them to consider how unsafe driving can take family members away from their loved ones forever. Please drive safe out there, we are depending on you in more ways than one.

If you or a loved one have been in a catastrophic crash with a semi, and want to speak to an attorney to see if it had anything to with safety, please give our Personal Injury Team a call in Fargo, ND at 701-297-2890 or send an email via the contact form below.