"52hp" sounding way smaller than "38kW" is the fault of cars built for markets with a history of well-off people living in suburbs, yes.

One of the tags on this post, "#this is cars fault probably", inspired me to write a post about just how much power the average car has per passenger, comparatively — if you're wondering why I qualified the title the way I did, I'll get to that. Basically, though, it's a combined issue of physics generally, the usual operations of various categories of vehicle, and the assortment of political and economic factors that have shaped the built environment and travel patterns in the most "car-brained" countries in the world.

How much power is 52hp?

Well, for accuracy's sake, the post I was inspired by was talking about 480V at 80A as compared to 38.4kW as compared to 51.5hp, so I will use those values. Wikipedia's assorted "orders of magnitude (measured quantity)" pages, such as for power and energy, are very convenient references for answering how relatively big some given quantity is, so I'll turn to those.

That's as much power as:

almost 1/100th of the power that the Titanic could put out at full steam
¾ of the transmitter power of clear-channel AM stations, which can, at nighttime, often be received from over 1,000km away
about 100× that of a person riding a bicycle under average (not sprinting) conditions
1.5× the maximum power draw of a house with a 200A power supply at 120V, which is fairly typical in Canada and the US
120 RTX 4080s running at peak power draw
the caloric needs of at least 1,500 human brains

It's a lot of power. You can do a lot with that power! And as I'll discuss later in this post, it's a lot more power than most cars usually use while in motion.

So what does a car do with that power? And how do other forms of transportation use their power?

First of all, some context for how vehicles use their power. If you scroll down to all the vehicle data I've put at the bottom of this post, you'll find the weight, passenger capacity, top speed, and power of a range of modes of transportation.

Cars

No matter what, cars involve rubber tyres on concrete and/or asphalt. This involves a decent bit of energy being lost to the substantial friction which is needed to let vehicles as relatively light as cars accelerate quickly and then maintain control. Cars with internal combustion engines and no option for charging batteries off of the power grid (so, pure ICE cars and non-plug-in hybrids) inevitably lose ~70% of the energy that they burn as heat before we even get to the power of their engines. Pure ICE cars add in extra inefficiency by having no regenerative braking, ensuring that any momentum which is bled off by braking gets turned directly into waste heat.

Pure EVs get closer to 70% efficiency, and have the most battery capacity with which to take advantage of regenerative braking; plug-in hybrids are a bit of a compromise between that and normal hybrids, and perform particularly well over short distances or other situations where the ICE doesn't need to kick in.

Freeways are the least worst case for fuel efficiency particularly for pure ICE cars, assuming a reasonable driving speed. This assumption doesn't always hold true. There isn't much braking, and the car's engine/motor is usually only putting out a tiny fraction of its peak power output to maintain a cruising speed. Accelerating on the onramp and passing draw on much more of a car's peak power, as do certain evasive manoeuvres and acts of road rage.

Conversely, the mode of operation for cars on urban streets is start stop start stop start stop, basically. This pushes a car higher into its power output more frequently, likely for a longer cumulative period of time, and involves more energy being burnt off during every inevitable round of deceleration. Hybrids, plug-in hybrids, and EVs can all recover a fair bit of energy from each application of the brake; on the other hand, pure ICE cars do not.

Buses

Express buses are probably going to have the same kind of behaviour as cars on any given stretch of road, though HOV/transit lanes give them an advantage in terms of avoiding congestion. Local buses are going to stop and start at least as much as cars do.

Rail

Trains are far heavier vehicles with far less friction for their size, due to both having a tiny front profile compared to their length and using steel wheels. Electric trains can have an efficiency of up to 90%; diesel-electric trains peak at 30-ish %.

Trams, depending on their alignments, can operate like anything between a local bus and an express bus in terms of speed and start/stop frequency. Subways tend to fairly consistently travel between a few hundred metres and a few kilometres between stops; commuter and regional rail tend to go several times further between stations. High speed trains, depending on their alignments, might make extremely sporadic stops between long segments at high speeds, make more frequent stops, or adjust their speed up and down frequently to switch between legacy tracks and high speed tracks.

…so what's with the "built for markets with a history of well-off people living in suburbs" qualifier?

Take a look at the average weights of cars in EU member states as of 2015. And then consider the average weight of passenger cars in each of Canada, the US, Australia, and New Zealand, all of which are close to two tonnes. Sure, there's the whole perverse incentive cycle of US fuel economy regulations which omitted "light trucks" which eventually set off a "make cars heavier so they won't lose in crashes" arms race, but the problems started a few centuries before that. Not with Reagan, not with Goldwater, and not even with the Union's failure to purge Confederates and other supporters of slavery during Reconstruction, but with the entire settler-colonial project.

When you're stealing more land than you could ever use, not only are you in a political position to use land vastly less efficiently — there's every incentive to ramp up that inefficiency, at least to the extent that you can still run a state capable of repressing resistance and dissent while facilitating efficient commerce. And even when you start bumping up against the limits of what infrastructure you can sustain, that option still exists in a way that it doesn't elsewhere.

Which is what enabled an almost maliciously incompetent (on top of the actual malice which pervaded every step of the colonial land allocation process) approach to allocating land in the first place, leading to an unnaturally inefficient distribution of communities, and which is what later enabled white flight and the construction of affluent suburbs.

In addition to more generally salient problems like thousands of ongoing genocides that have been furthered through enclosing more and more land, the way in which mass adoption of single family detached housing where it doesn't make sense buttressed the nuclear family and enabled an intensification of familial abuse while escalating alienation to previously unseen heights, the role of the suburbs in entrenching racial segregation, and the way that massively inefficient infrastructure and overbuilt houses have played into a brutal expansion of financialisation throughout the economy, the ascent of the suburbs meant more powerful, more wasteful cars.

This occurred for the following reasons, among many others:

Suburbs are further out, requiring faster roads to produce acceptable commute times. While induced demand consistently negates the value of these faster roads in the long term, at least for a while (and generally at less busy times of day), people drive faster. This calls for more powerful cars.
In a cultural climate where You Deserve A ½ Acre Fiefdom :) was the dominant narrative, big, spacious cars were also an inevitability. These require more power.
Faster roads mean you're going faster, which requires quadratically more energy to pass at some given speed differential, make evasive manoeuvres, resist headwinds, or otherwise do anything that requires more speed. This requires more power.
Faster cars have more energy during crashes, requiring more robust safety systems. These weigh more. That means more power.
When the dominant mode of housing for a substantial portion of the population — the "middle class" — amounts to status symbol dickwaving, that's going to influence the designs of the second most expensive item people own/lease/rent as well.

But big, heavy cars have somewhat proliferated outside settler states as well. Look back at that chart of average car weights in the EU, and you'll see that Germany is pretty high on the list. The same country that's got the Autobahn network, parts of which have no speed limit. While Germans' taste in cars might be less garish than Canadians' or Americans', comfortably driving long distances at high speeds is absolutely helped by having a powerful car which is stable and secure on the road. In that kind of driving, having 200 extra horsepower you're usually not using can actually make a difference.

And why does Germany have this kind of road system? Well, it was started as a Nazi propaganda stunt, basically, but ⅘ of it was built after the Second World War. So I'm not going to say Autobahns Are Inherently Fascist or something. However, the FRG having vastly more enthusiasm for Autobahn expansion than the GDR seems to me (and I'm engaging in a bit of conjecture here) to be influenced by factors beyond just all the Marshall Plan money they were getting. An economy where income inequality is (to an extent) a feature rather than a bug or compromise, combined with desire to cultivate an appearance of individual prosperity and freedom, in addition to a large pre-existing heavy industrial base with decades of experience building automobiles, is going to end up with things like suburbs, an emphasis on private transportation, and car manufacturers which are ready to take advantage of people needing to drive long distances.

It's Capitalism, Babey. Basically.

So how much of this power is actually moving people?

In short: not a lot. I've put all of my more precise data points for the comparison down at the end of the post, so as to spare you from having to read through a bunch of bullet points worth of statistics about vehicles before getting to actual substance. (I'm also not talking about airplanes here. I was going to, but converting from thrust to power is more inexact than I'd like to get.)

I'm going to use the average adult weight in whatever country a given vehicle is either manufactured or operates in (which will be indicated in the data below) to calculate the vehicle weight:passenger weight ratio on a case-by-case basis. For discussing the efficiency of cars, I'm going to use the 2019 figure for average car occupancy in the US, 1.5 people per vehicle, throughout this post. I'm going to assume 50% load for everything else, given how many transit agencies don't publish data that could be used to calculate load factors without, say, somehow finding out exactly how many trips are run by which vehicles on which days and making the relevant calculations from that.

First of all: sorting through the data I've got based on what percent of a given vehicle's average weight is passengers, high-speed trains appear to be have the lowest ratio. Under normal conditions, maybe 5% of a train's weight is passengers. Cars typical of the North American market are at around 6%, with increasingly slower trains more or less being better, and a bicycle (unsurprisingly) being best, at better than 80%. This makes some sense — faster trains, much like faster cars, need heavier safety systems to reduce injuries and fatalities in worst-case scenarios — and unlike heavier cars, heavier electric trains can convert a basically indefinite amount of their momentum back into electricity via regenerative braking, thanks to having third rail or catenary power instead of batteries.

If we're looking at power per average number of passengers, though, the incredible, disproportionate power of cars built to safely and comfortably handle long freeway drives becomes apparent:

Bike: 1kW (once again, this is under exceptional conditions!) per passenger
Waratah trainset (Sydney Rail): 4.88kW per passenger
New Flyer XT40 trolleybus: 13.89kW per passenger
N700S Shinkansen trainset: 25.8006kW per passenger
Smart fortwo: 26.67kW per passenger
Toyota RAV4: 84kW per passenger

While a high speed train might need a ton of power to accelerate up to 300km/h quickly enough to actually maintain that speed for long enough to make it being capable of that speed worthwhile in the first place, it'll usually just get up to that incredibly high speed and then let momentum do most of the work. Conversely, a car that's intended for use nearly exclusively in town can get away with not that much power because it's barely ever going to need to get above 100km/h, and will usually be staying around 30–60km/h.

Energy management in a freeway-capable car, on the other hand, involves the same kind of weight/payload ratio as a high speed train, all the chaos and ups and downs of a tiny car or bike, and a velocity where the quadratic nature of kinetic energy and drag really start to kick in. You aren't accelerating to cruise speed and staying there until it's time to decelerate such that you'll stop at your destination, or making quick little speed adjustments — you're jumping up and down in speed all the time, hemorrhaging momentum to your brakes, drag, and additional friction losses when taking turns tightly.

So yes, 38kW per passenger is a lot. It's as much as the fastest trains out there can put out when loaded at a ⅓ load. It's "can get you going 4× faster than an average highway driving speed" lots of power. But for the hyper-specific vehicle use case that accounts for a huge portion of mobility in countries like the US, it's not enough.

Specific data

All weights are kerb for cars and buses and nominal for trains.

The cars I used as examples here are:

To stay close to the 51.5hp figure, the 0.8 cdi version of the 2nd generation Smart fortwo, which is a 750kg car which can carry two passengers at up to 135km/h with a 40kW/53hp engine.
For something that's representative of the average car in wealthy, highly suburban countries (so, something close to the 1,626kg median weight of the US passenger car fleet as of 2017), I'll go with the most popular Not A Pickup Truck in Canada and the US: the Toyota RAV4. In keeping with the fortwo above, I'll go with the 5th generation's base model, which is a 1,530kg SUV which can carry five passengers at up to 185km/h with a 126kW/169hp engine.
Of course, I'll also include the most popular passenger automobile in both Canada and the US, the Ford F-150 — specifically the 14th generation's base ("XL") four-door model, which is a 1,823kg pickup truck which can carry six passengers at up to (at least) 170km/h with a 220kW/290hp engine.
And while we're at it, I think the Tesla Model 3 is probably pretty representative of the electric car fleet as it currently exists. The current base RWD model is a 1,762kg car which can carry five passengers at up to 225km/h with a 208kW motor.

A bicycle plus some bicycle-related accessories (such as a helmet, lights, and a lock or two, so on) often adds up to about 15kg, and can carry one passenger (tandems are very much an edge case, IMO) at a sprint speed of 55km/h with an extremely limited short-burst power of about 1kW. Unlike every other method of transportation I will be discussing here, human physiology severely constrains how often that peak performance can be hit and how long it can be sustained.

Reference points for buses:

To represent a typical diesel bus, I'll use the Nova Bus LFS HEV (40'). This is a bus which probably weighs somewhere around 12,981kg (though weight figures for it aren't provided officially anywhere) which can carry 81 passengers at probably somewhere below 100km/h with a 209kW/280hp engine paired with a 200kW electric motor.
I'll fit in some Winnipeg representation here by using the New Flyer XT40 as my point of reference for a trolleybus. It's a 14,913kg bus which can carry 72 passengers at up to 72km/h with motors adding up to 500kW.
The BYD K9M is fairly representative of battery-electric buses. It's a 14,601kg bus which can carry probably about 74 people (assuming one standee per seated passenger, which seems to hold true for a lot of buses) at up to 105km/h with 300kW worth of motors.

And rail vehicles:

I think the Bombardier (now Alstom) Flexity Berlin (in its 5-segment configuration) is a decent representation of a modern low-floor tram. It's a 37,900kg tram which can carry 180 people at up to 70km/h with 400kW of motors.
For a metro vehicle, I'm going to resist the temptation to just throw the Mark III SkyTrain rolling stock in here (because multiple vehicles from the same company in the same post seems unrepresentative, let alone the oddball LIM propulsion of the Expo and Millennium Lines), and instead use the MTA's R160B trains, built by Kawasaki. (I figure the B Division will have rolling stock more in line with the average metro worldwide than the A Division, which has fairly small trains.) Many of the trains of this type are configured as 5-car trainsets weighing about 193,000kg, which can carry 1,218 people at up to 89km/h with 2,200kW worth of motors.
For commuter/regional rail, my example will be Sydney Trains' Waratah trainsets, built by Downer Rail and CRRC, which are 407,000kg trains that can nominally carry 1,200 people (though possibly many more under a crush load) at up to 130km/h with 2,928kW worth of motors.
A good example of high speed rail (as in, a widely exported technology which isn't by a manufacturer already represented on this list) is the N700S Series Shinkansen by Hitachi and Nippon Sharyo. This is usually configured as a 16-car, 700,000kg consist capable of carrying 1,323 people at up to 300km/h with 17,080kW worth of motors.

If you're looking for a reference for airplanes, the LM9000, which is an electrical generation gas turbine based on the GE90 (two of which carry each original Boeing 777), apparently puts out 74,285kW.

Average weights used for weight calculations:

Germany, ≥18: 77.7kg
Canada, 6–79: 72.2kg — I'm using this for the RAV4 as is the 2nd best selling automobile in Canada as opposed to the 5th or 6th best in the US. (This also applies for the LFS HEV and the XT40.)
US, "adults": 82.1kg. This applies for the F-150, Model 3, and R160.
China, "adults": 64.4kg.
Australia, ≥18: 78.5kg.
Japan, "adults": 59kg.

Zuthal

@Zuthal