The Physics and Economics of Moving 44 Tonnes at 56mph

> At 0.5 mph differential, the overtake takes 291 seconds — over a minute of blocking the outside lane. Annoying, but it gains the driver 5.0 extra miles across a working day.

The driver gets there 5 minutes earlier in exchange for causing a 7-km tailback multiple times per day? That seems like exactly the kind of thing that should be regulated away: the truck in front is limited to 90 km/h, you're limited to 90 km/h, you should expect to travel in convoy with that truck even through manufacturing tolerances mean your limiter is actually set to 90.5.

If the 0.5 km/h is actually valuable to the trucking industry, they can invest in more precise limiters at scale.

I was reading the NASA truck aerodynamics thread earlier and realised that commercial freight is one of those fields that touches everyone's daily life (everything you own arrived on a truck) but sits in a complete knowledge blindspot for most people.

I work in fleet fuel efficiency and wrote up the foundational mental model, covering why trucks weigh what they weigh, why they're all doing exactly 56mph, why diesel is so hard to replace, and why 1% fuel savings matters when you're burning 43,000 litres a year.

This is the first in a series, there's already a 2-part deep dive on hydrogen up as well. Tried to keep it accessible without dumbing it down.

Maybe they should give the trucks a "turbo boost" button that lets them increase speed by something like 5 KM/hr for 120s every 30 minutes. Just enough to allow truck drivers to pass now and then without causing these types of log-jams on the highways, without causing safety problems. I'm sure there's a more correct combination of speeds and times than this.

Sort of like the silly "boost buttons" on the Honda CR-Z [1] or the Elantra N [2], but just lifting the speed limiter for a bit...

[1] https://en.wikipedia.org/wiki/Honda_CR-Z#Powertrain

[2] https://en.wikipedia.org/wiki/Hyundai_Elantra#Elantra_N/Avan...

> This isn’t advisory. It’s a physical limiter in the engine’s ECU. The truck cannot go faster.

I live in Latvia (in the EU) and see a significant part of our ARTICs on the roads go well past 90km/h daily. I presume their fleets do monitor the speed and alert the driver if speeding for a prolonged period of time but they are obviously not physically limited. Maybe the limits do come from the factory but get disabled? I really couldn't say.

A recent journalistic investigation uncovered a problem with the weight limit not being followed on a mass scale too. Specifically by our lumber industry whos drivers are incentivized to break the law. Even if you see a dangerous overloaded truck on the road and call the Police, it is likely no action will be taken because there only a couple of units in the country that are equipped to weigh a freight truck out in the field.

For people that want to make the calculation: A truck does not need a 15 ton battery. In Europe, we have mandatory breaks for truck drivers. So you need a battery pack for max 400km of range, let's say 500km. When you have a break, you charge. For this, you need like 1500kWh battery pack, which weigths like ... wait, 15 tons. But this is not entirely correct, the real values reported are between 120-150Kwh/100km, that means a half of the stated number, 7.5 tons for the battery pack.

> Driver training that closes the 15–20% gap between the best and worst operators in a fleet.

As a naive non-trucker, I'm surprised to hear that the difference between the best and worst operator is this significant. I realize it's a bad look, and shows I thought this was a low-skill job, but I'll be honest and try to call out my own prejudice. It's cool that skill actually does have a large impact here.

> The truck cannot go faster. Floor the throttle at 56mph and nothing happens. The fuel injection is electronically capped.

Man, that's kindof scary -- if for some reason the truck legitimately needs to go faster (eg, escape a warzone, a flood, a wildfire), it cannot do so. I'm sure this was a calculated design decision, but on the surface I'd prefer if the speed was logged and then checked at regular intervals (perhaps with automated reader). That would also allow for easy updates to the limit, tighter restrictions in specific areas, etc. I wonder what all the factors going into this design decision were.

The (bad) justification for overtaking seems a much better justification for the slower truck to fix their calibration and go faster.

Lots of good info but it all feels a bit like it is being used to create a "just so story" to support whatever the current status quo is.

I'd buy into the efficiency and economy arguments more if the truckers would stop dumping gallons of diesel on the roads.

Argh the liberal admixture of different units (mpg, kg, L, hr) in the first table really brings home that this is a UK piece.

Interesting, thanks!

One thing I'd update is that early in the article you say that for switching from diesel to lithium-ion, "It's 16 tonnes of payload that disappears".

But then later you take engine efficiency into account and say it's "about 6.4 tonnes of battery".

So the claim that it would ever reduce payload by 16 tonnes seems incorrect, and not everyone is going to read both parts.

The article makes it sound like the Tesla Semi is physically infeasible. Yet, it is in active use on a sufficient number of long-haul routes that ignoring this proof of existence undercuts some of the central points the post tries to make.

The combination of higher efficiency, regenerative breaking, and some regulatory wiggle-room such as slightly higher allowable gross-weight (2000 lbs in the US, and 2000 kgs in the EU), together with reduced maintenance cost and time significantly affect the economics of trucking.

As regulatory frameworks price in more externalities of internal combustion engines, such as the climate and health effects of their emissions, burning diesel will no longer make economical sense. All road transport will end up being battery-electric. The declining cost of owning and operating electric vehicles compared to internal combustion ones will reach this point even without regulatory changes, just at a slower pace.

> Rail is superb for what it does: moving bulk commodities... The problem is last-mile.

Before around 1950x-1970x rail networks were more dense (at least in Europe) - any significant goods source/destination (like a warehouse, a factory e. t. c.) had a railway spur. Lots of rail tracks / spurs were abandoned /removed when it was widely believed that trucks are the future and railways are outdated.

If all these spurs were kept last mile problem would not be as bad for railways. Also electric trucks are well suited to solve this last mile problem.

Is this correct — HGVs can go faster on dual carriageways than motorways?

"UK speed limits for heavy vehicles are also more complex than most car drivers realise. Articulated trucks over 7.5 tonnes: 60 mph on dual carriageways, 50 mph on single carriageways, 56 mph (limiter) on motorways"

Not able to find a source that verifies that

It seems like trucks are a use case where battery swapping would make a lot of sense. Unlike with cars, the battery doesn't need to be a structural element, and there's much less need for it to be a strange shape, as in some cars.

> The five minutes of inconvenience to you saves them meaningful time and money over the course of a day.

Assuming my time and everyone else stuck behind them combined is far less valuable than the truck driver.

>Most assume the truck driver is being inconsiderate.

You could probably add a whole section of specifically learning to drive a car with trucks on the road to driver education programs and it would do wonders for traffic.

>Anti-idle ordinances exist in several US states and EU regulation is moving in this direction.

Yep, grab a sleeping bag or take your clothes off and use evaporation cooling on yourself. The good news is that car/van camping stuff can apply to trucking as well and that is fairly popular these days.

Another option is simply having places to sleep outside of the truck that are powered by solar/wind and don't cost anything to truckers, but that's only viable when we actually care about reducing emissions over profit.

>Every kilogram you add to the vehicle is a kilogram you can’t carry as freight.

You can save a bunch of weight by not having the sleeper cab if you can readily stop somewhere for a safe place to sleep. There's quite a bit of frontier savings you can do by externalizing costs of transporting stuff to other industries (aforementioned free hotel rooms) and getting tax payers to pay for it, which makes a ton of sense here since trucks are transporting all of the food we eat.

Why is fuel consumption 5x more per mile but 10x more per hour, if the trucks are moving more slowly than cars?

Tangential, do vehicles detect motion by crosswind or road camber and compensate? I saw some social media post of lots of trucks toppled over by crosswind.

great article but the 44 tonne limit is not "physics", it is regulation. if an electric truck would be allowed to weigh 5 tonnes more all these calculations would be different.

How is fuel consumption per mile 5x but fuel burn per hour 10x?

> An electric drivetrain achieves around 90%, so you only need roughly 1,600 kWh of battery capacity for equivalent range. At 0.25 kWh/kg, that’s still about 6.4 tonnes of battery — roughly 18 times heavier than the 350 kg diesel tank and fuel it replaces

This misses the fact that the motor and transmission on an electric truck is lighter than the diesel. This doesn't completely negate the issue but it does help and is not mentioned.

The 15 liter diesel engine is about 3500 lbs and the transmission with many gears is another 700 lbs.

The Tesla Semi has 3 model S motors with single speed transmissions each one is about 300 lbs with inverter so there are at least 2-3000 lbs weight savings in the drivetrain to consider.

In the US Electric semis get an extra 2000 lbs payload allowance too too so they can be 82k lbs total rather than 80.

>. That’s roughly 28 to 35 litres per 100 km, or around 30 litres per hour at cruise speed. This is not a misprint. A truck burns in an hour what a small car burns in a week.

Let me paraphrase - a truck weighting 25 times more than a car burns only 4 times as much fuel per 100km at corresponding cruising speeds.

> At 0.25 kWh/kg, that’s still about 6.4 tonnes of battery — roughly 18 times heavier than the 350 kg diesel tank and fuel it replaces, and 6.4 tonnes of payload that disappears from every trip.

And how many tonnes of internal combustion engine, gearboxes and plumbing? It is not an insignificant matter

the one being overtaken could release the throttle for a moment...

THE ONE BEING OVERTAKEN COULD RELEASE THE THROTTTTTTLE...!!!

:)

These large trucks must go. While the mentioned numbers make some economic sense (cost per tonne transported etc.), the road wear is excessive due to the fourth power law. Most cargo can be split into smaller chunks.

> A diesel fuel tank for 400 litres of diesel weighs roughly 350 kg (the tank itself is relatively light; diesel is 0.84 kg/L). A battery pack storing equivalent energy would weigh on the order of 16 tonnes at current lithium-ion energy densities. That’s not just additional weight. It’s 16 tonnes of payload that disappears.

And yet, electrical semis exist that come without 16 ton batteries. The fallacy here is that most of the diesel is used to heat the universe rather than move the truck. Truck engines are relatively efficient but it's still a combustion engine. EV trucks are now a reality.

Mercedes-Benz’s eActros 600, one of the flagship battery-electric long-haul trucks now in series production, uses *three 207 kWh LFP battery packs for a total of 621 kWh of installed capacity, and under realistic conditions can deliver about 500 km of range on a full charge with a 40-ton gross combination weight, with opportunity charging in driver breaks enabling well over 1 000 km of daily travel. That's 4-6 tons of battery, not 16.

Volvo Trucks’ current flagship, the FH Electric, has 360–540 kWh of batteries (four to six packs) and achieves up to ~300 km of range for typical heavy-duty operation, and its forthcoming FH Aero Electric long-haul variant is being announced with ~780 kWh battery capacity targeting ~600 km of range. That's around 3 tons of battery.

The weight goes at the cost of the useful load. Though the EU allows an extra 2 tons for new energy trucks. And of course a lot of trucks aren't fully loaded typically. Also, the weight limitations have a lot to do with safety issues related to diesel trucks and their brake systems that electrical trucks have much less. Regenerative braking and lots of torque at low speeds mean that they could move a lot more weight safely than currently allowed. And adding more axles to distribute the weight can address any road damage concerns.

With mandatory 45 minute breaks every 4.5 hours, trucks can just top up as needed. With normal truck driver hours that's 1 or 2 breaks in a working day. There's a growing amount of chargers all over Europe and these things routinely drive all over Europe from Scandinavia to Iberia to Balkans and everything in between. There are of course still many places where more/better chargers are needed but these ranges are usable and practical enough that you can get loads from A to B in most of Europe with only minimal delays relative to diesel trucks in terms of charging time losses. It's early days and charging infrastructure is rapidly being improved. But the point is, that electrical trucks work just fine today. There are no fundamental real load or distance limitations here. But of course more infrastructure is needed to scale.

Lighter batteries will make trucks slightly more efficient. But price and longevity matter much more. Sodium ion with its well over a million mile lifespan looks like it should revolutionize trucking over the next decade. LFP is commonly used today already. NMC is lighter but has a lower lifespan.

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Long haul trucking should be illegal or effectively eliminated by a carbon tax. Use trains for long hauls.

He even said the problem with trains is last mile. Last mile short haul trucks can be and are electric.

It's weird he laid the groundwork for this argument, but he isn't making this argument.

Fix the infrastructure issues that make transferring from rail to truck difficult. Yes, that's challenging and expensive. Guess what else is? The status quo, and the effects of climate change.