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The Physics and Economics of Moving 44 Tonnes at 56mph

mikeayles.com

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Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#21

Post by hnthrow0287345 »

>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.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#23

Post by RobotToaster »

dmurray wrote: post #8

> 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…

From a commercial perspective, you would think the fuel savings from slipstreaming would more than make up for those five minutes.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#24

Post by mikeayles »

NomadicDaggy wrote: post #11

> 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?…

Probably the first thing to consider is the trucks have their speed calibrated periodically to ensure the accuracy of their tachographs (in the UK at least) so a truck doing 90kmph may show as 100kmph+ in a passenger car, I know my Volvo is 7% out, and my Seat is closer to 10% out.

That said, depending on the truck, there's fuses you can pull, ECU remaps and even for the older trucks with the magnetic sensor in the gearbox, the trick is/was to stick a magnet on the sensor (with a bit of string, so you can pull it off remotely if you get pulled over). All of these methods are becoming less feasible, as things like the aggregate wheel speed sensors used for ABS get used, you can't just fool one thing now.

As for the weight limit problem, that's a whole other rabbit hole!

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#25

Post by [deleted] »

WJW wrote: post #20
schiffern wrote: post #19

Earlier quoted context omitted.

It seemed like the author had moved on from EVs so I thought he was done, but okay. Should've finished I guess. The article still never accounts for the fact that motors+inverters are ~2 tonnes lighter than an engine+transmission.

Or your reading comprehension is not good enough. I didn't have any problem finding the paragraph where he author goes into extra detail. Who can say.

[deleted]

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#26

Post by Reubachi »

gruez wrote: post #17
dmurray wrote: post #4

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

Yeah the numbers in this article are all over the place. "291 seconds" also got rounded off to "over a minute", when it's closer to 5 minutes

That is simple, that one (very cool) interactive matrix only has that one output description regardless of the input. The effect is clear either way

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#27

Post by [deleted] »

WJW wrote: post #20
schiffern wrote: post #19

Earlier quoted context omitted.

It seemed like the author had moved on from EVs so I thought he was done, but okay. Should've finished I guess. The article still never accounts for the fact that motors+inverters are ~2 tonnes lighter than an engine+transmission.

Or your reading comprehension is not good enough. I didn't have any problem finding the paragraph where he author goes into extra detail. Who can say.

[deleted]

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#28

Post by secult »

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.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#29

Post by close04 »

dmurray wrote: post #8

> 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…

> That seems like exactly the kind of thing that should be regulated away

This is regulated via "no overtaking by trucks" [1] signs on portions of road that are susceptible to formation of queues, or more dangerous road conditions.

P.S. To bundle some replies:

> but they only apply during busy hours

Don't remember ever seeing the time interval next to these signs. They are tied more to the location than the time. But that's not bad? The goal is to avoid the worst issues, not to force trucks to drive in an ordered line for 8h straight. Traffic lights also sometimes turn to intermittent yellow late in the night. Why spend a few minutes alone in the middle of the street for a red light?

> Does it still make sense for that to be "default allow?" Why doesn't the trucking industry lobby for every Truck Overtaking zone

The default should be the the one that applies most of the time. Today that's the "allow overtake". I'm allowed to very slowly overtake in my car. And I've seen this when I was driving right at the speed limit and someone else was overtaking at something like 1cm/s. It was painful to watch, at some point I just slowed down a bit to let him get in front and release the left lane.

If you ban truck overtakes and allow them only in specific zones, you'll quickly have kilometers long truck queues that never get drained. For an overtake that takes 1 min at 90km/h the trucks traveled 1500m. Many highways are 2 lanes so just one slow truck on the right lane and one slow car on the left lane screw the entire highway. Those costs go to you whether you're in your car or buying something those trucks deliver.

[1] https://media.gettyimages.com/id/1728143251/vector/no-overta...

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#30

Post by mikeayles »

gruez wrote: post #17
dmurray wrote: post #4

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

Yeah the numbers in this article are all over the place. "291 seconds" also got rounded off to "over a minute", when it's closer to 5 minutes

Good spot, and gruez is right about the caption too (fixed both, thanks).

The car's L/hr figure was wrong. At 45 mpg (imperial) and 70 mph cruise, a car burns ~7 L/hr, not 3. That makes the flow rate ratio ~4x, which is consistent with 5x per mile and the truck travelling 20% slower.

The ~3 L/hr I originally had is what you'd see as an average over a mixed driving cycle — ~30 mph mean across urban, suburban, and motorway. I was carelessly mixing the cars combined-cycle flow rate with the truck's cruise-only figure in the same row.

The truck doesn't have this problem because a long-haul artic genuinely spends most of its operating hours in that narrow 50-60 mph cruise band. "Average fuel burn rate" and "fuel burn rate at cruise" are nearly the same number. For a car they're very different, transient acceleration, idling in traffic, and low-speed urban driving all drag the average flow rate down well below the motorway figure.

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