There are real world range tests for Tesla Semi, Freightliner eCascadia and other electric Semi trucks at the Run for Less event. Truck average driving speed is critical to the comparison of the real world ranges. People who lived through the 1970s and 1980s know that there was strict enforcement of 55 mph speed limits. This was implemented in response the oil crisis when OPEC was created and increased gas prices from $0.36 in the year before the crisis to triple a few years into the crisis.
The Tesla Semi can get 500 miles with a full load but only when driving with an average speed of about 52.5 mph.
Driving at 55mph would save 15-30% of fuel than driving at 65-80 mph.
CORRECTION: The National Maximum Speed Law (NMSL) was actually signed by Nixon. The NMSL was modified in 1987 and 1988 to allow up to 65 mph (105 km/h) limits on certain limited-access rural roads. Congress repealed the NMSL in 1995, fully returning speed limit-setting authority to the individual states. The Emergency Highway Energy Conservation Act was a bill that included the National Maximum Speed Limit. States had to agree to the limit if they desired to receive federal funding for highway repair. The uniform speed limit was signed into law by Nixon on January 2, 1974, and became effective 60 days later, by requiring the limit as a condition of each state receiving highway funds, a use of the Commerce Clause of the United States Constitution. The 55 mph (90 km/h) National Maximum Speed Limit was made permanent when Congress enacted and President Gerald Ford signed into law the Federal-Aid Highway Amendments of 1974 on January 4, 1975. Joan Claybrook, head of the NHTSA under President Jimmy Carter, in an effort to get people to pay attention to there now widely ignored law, passed a rule requiring that new vehicle speedometers have 55 mph bolded and not have the ability to indicate speeds higher than 85 mph.
The legislation required 55 mph (89 km/h) speed limits on all four-lane divided highways unless the road had a lower limit.
In 1984, rocker Sammy Hagar had the hit song… I Can’t Drive 55 as rebellion to the highway speed mandate.
There is a research paper that goes over aerodynamics, speed and payload weight in regards to energy usage of an electric truck. 65 mph is 95.3 feet per second and 52.5 mph is 77 feet per second. The part of equation that deals with speed is squared. Basically you lose 15% of your range driving at 65 mph versus 52.5 mph in an electric truck pulling max load.
Why would a truck driver choose to lose 15% range? Driving 400 miles at 65 mph takes just over 6 hours. Driving 400 miles at 52.5 mph takes over 7 and a half hours.
One of the Pepsi Tesla Semi on Day 3 had 303 miles of range on three partial charges totaling 69% of the charge. This would mean 440 miles on 100% use of charge. The Tesla Semi was mostly driving at a speed of 63 mph.
A Freightliner eCascadia was able to get 100% ranges of up to 280 miles while other eCascadia had 100% ranges of 220-240 miles. The longer range drive was keeping a speed of 55 mph.
Comparing ranges at the higher speed driving (62 mph) would see ranges of 440 for the Tesla Semi vs 245 miles for the eCascadia.
Comparing ranges at the lower speed driving (52-55 mph) would see ranges of 500 for the Tesla Semi vs 290 miles for the eCascadia.
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When trucks are eventually driving autonomously without drivers, it will matter less if average speed is lower. There is also the already tested method of driving in convoys to reduce drag significantly.
The Tesla semi is a good short to medium haul truck. It’s terrible for long haul, not only because of the range penalty but also the recharge time. Time is money, a lot of it, for truckers doing long hauls. “With short stops and breaks, a trucker may not operate their rig for more than 14 hours after a 10 hour stop. Short breaks, as well as time in the sleeping berth of their truck, are required for truckers to meet their FMCSA requirements.” Those short breaks can become long costly ones if an electric truck has to pull over, search for a charging station that isn’t already in use, and hope that it’s a fast charging one. Having a home depot with that all set up to work overnight is OK. Otherwise, it’s unworkable until new battery types make both range and charge times better. https://www.youtube.com/watch?v=t7vlNLfdglE
Or until autonomy means they don’t have to stop for sleep.
The 55 MPH speed limit was initiated by President Nixon on November 26 1973 and he signed the legislation in early 1974 to save gas. The law was repealed when OPEC’s 1973 oil embargo was lifted.
Yes, Nixon signed the Emergency Act, phased out in 1987. https://en.wikipedia.org/wiki/National_Maximum_Speed_Law
I’ve seen the huge energy usage from driving my hyundai kona electric car at highway speeds. The way I’ve fixed this is not by driving slower but by following behind the fastest semi on the highway. Cruise control and front vehicle detection make it easy to follow or keep up with semis that slow down and speed up depending on driving conditions. It’s an absolute must to combat range anxiety for electric vehicle drivers.
To Rick C. No! Most states do not limit tractor trailers to a 55 mph limit. If they did, even more drivers would be falling asleep because of the slow pace.
We’re gonna need to add more lanes to the interstates. Not gonna be held up by no 52 MPH trucks.
Actually, throughput is not really a function of speed. As long as trucks are in the rightmost lane, they shouldn’t be impacting capacity much, or causing much delay.
Well … then there’s physics.
The retarding friction of a freightliner (or car, or airplane or bird or rock) depends not just on its velocity to the third power (air displacement friction), but also on rolling friction. This is why heavier loads always require more power than lighter loads.
The power (energy per second) needed for steady-state (unchanging velocity) wheeled transport is best characterized by the non-formal equation
P ≈ Ka⋅V³ + Kr⋅V² + Km⋅V
Where (Ka) is the factor associated with airflow. Airfoils. Aeronautics. Shape, frontal area, all that. And (Kr) is the factor having to do with normal resilient-surface friction (“rolling” friction), for pneumatic tires, not-as-hard-as-you-think pavement, shock absorber losses and all that. The last factor (Km) is mechanical friction, which is best just a linear relationship to velocity. The engine, the transmission, the effects of the frame of the vehicle.
So whilst it is convenient to say P ≈ kV³ and then go on to compare 65³ ÷ 55³ = 1.65 and then say, oh, oh, it takes 65% more power (then divide by the ratio to find energy-per-mile) of 40% more per mile… it is insufficient at best.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Cool. I notice quite a bit of difference in the Km*V factor you mention among my personal vehicles. The modern minivan will coast forever; the drivetrain in the old classic is a lot more lossy.
Historically, new things are adopted over older proven things because they are demonstrably better in most respects (Model T was better than a horse), iPhone better than a Nokia brick (except battery endurance). There are a lot of articles trying to elaborate on the slim benefits of current BEV compared to ICE. The BEV just aren’t there yet…. Showing some kind of ripple curve with periodic partial charging and driving the semi… Act like energy is scarce when it isn’t, for Gaia’s sake.
And seeing these huge multi-hectare mega factories in China – whew! Kinda glad we’re not clearing land for similar factories, but alas, a dozen new multi-hectare warehouses have gone up around me where orchards used to be.
A couple of items to think about. Civil Engineer here who designs highways and is involved in the NEVI program for E-truck Charging. Right now we are at the chicken and egg part of charging for Semis. I have a wait-and-see attitude.
The Feds did toss in $5.0 Billion to get this started but that is just a drop in the bucket. I think platooning will need some major modifications to the interstate system. The current interstate pavement is not built for the type of continuous load that platooning will have. The pavement will rut out fairly quickly, concrete might work but the politics of that probably won’t work. The largest contractors in most states are the largest asphalt companies. No way they let all that money go away from them. Ports are interested since they lower their emissions.
I’m not sure autonomous vehicles will be allowed unless you can find a way to make up for the loss of revenue from the accident attorneys. Even if it works you have to find a way around those guys, that aren’t going to give up without a fight. They also give a lot of money to state legislators. Just saying.
Peanut farmer wisdom; bless his heart.
Yes, P ∝ v^3.
One more thing to add, don’t most states limit commercial trucking to a maximum speed of 55 mph anyway?
No only in California most States are between 65 to 90mph it all depends on were you live
Well yes, it takes less energy to drive slower. But do you really want to drive a really enticing sports car* at 55 mph?
*looks over at one of his vintage Italian sports cars in garage. Vroom vroom.