Semi trucks have many options for fuel

Recently, the energy decline movement has proposed a new idea: large semi trucks cannot run on any fuel other than diesel. Only diesel offers the combination of high energy density for long hauls, and high torque for heavy loads. There are no other options, besides diesel, to power heavy long-haul trucks. This idea is found in this video (25:00), and also other places in this movement.

In particular, gasoline is not suitable for heavy trucking because of a lack of torque. Large diesel truck engines often produce 1,500 ft-lb of torque, which is several times higher than even the largest gasoline SUV engines. This amount of torque is necessary to haul heavy loads, so gasoline engines cannot do it, not even in theory. Or at least, so goes the claim.

This idea is not correct. Heavy trucks could easily run on gasoline or many other fuels. The torque of gasoline engines could easily be increased using a simple gear reduction. A simple 3:1 gear reduction would increase the torque of gasoline engines (and decrease the RPMs) so that the torque is far higher than a diesel engine. A gear reduction decreases RPMs and inceases torque, which is one of the main purposes of the transmission in almost every motor vehicle. 

No combustion engine has enough torque to carry heavy loads if it's connected directly to the drive shaft. Neither diesel engines nor gasoline engines could do it. For this reason, a transmission is required to increase the torque of the engine, both for diesel and gasoline engines. Gasoline engines simply require more of a gear reduction, that's all. As a result. it’s obviously possible to increase the torque arbitrarily by using gears, after which, gasoline engines could easily be used to power heavy trucks.

Large semi trucks frequently already have 2 (sometimes 3) separate transmissions in series, with 12 or more separate gear combinations. Adding another simple gear reduciton would only modestly increase the complexity and wear of the transmission.

There is also another way (besides gears) for semi trucks to run off gasoline. We could use gasoline-electric trucks, where the engine is not connected to the wheels at all. The gasoline engine drives a generator, which generates electricity, which powers an electric motor and drives the wheels. This kind of setup is already widespread and is used in almost all locomotives, many large articulated city buses, and a few passenger cars (Mazda MX-30 and Honda Clarity). In these vehicles, the torque of the engine is completely unimportant because the engine is not connected mechanically to the wheels. In this case, only the power of the engine is important, and even some big SUV engines have sufficient power to drive a large semi truck.

This issue is important because EV adoption is growing rapidly and could cause a reduction in gasoline demand. It's at least possible that gasoline demand will drop to zero or very low levels over the next 50+ years. If this happened, then there would be more than triple the fuel available for long-haul, heavy duty trucks, provided they could use the fuel no longer being consumed by passenger vehicles. If short-haul trucks like amazon delivery vans are also electrified, it would increase the amount of fuel available for long haul trucking by more than 5x because less fuel is used in other sectors of the economy.

As a result, we could easily have enough diesel and gasoline to power heavy-duty trucks for centuries.

These facts contradict one of the main doctrines of this doomsday group. One of the key ideas of this group was that trucks would suddenly stop running because of a shortage of fuel. However, that idea was not correct. There is enough fuel to keep trucks running for a very, very long time, using basic fuel switching which a market economy routinely carries out.

So far, in this article, we've examined the possibility of fuel switching for trucks, in particular, using gasoline for trucks which is no longer being consumed by passenger vehicles. However, that is not the only alternative energy source for trucks. Long-haul trucks could easily run off natural gas, electricity, coal, or woody biomass. Coal and woody biomass can be converted into diesel fuel using the fischer-tropsch chemcial process, which has already been in widespread use for many decades. Battery improvements are being implemented (such as solid state batteries) that would enable an 800+ mile range for long-haul trucks, which is more than they're allowed to drive in a day. As a result of these things, it's not clear that we face a shortage of fuel for trucks over any time period, ever, even millions of years from now. The far future is difficult to predict, and I expect humanity will end for other reasons at some point, but there is no inevitable trend, over any time period, which implies that trucks will stop running because of a shortage of fuel.