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Comment by dublinben | Hacker News Reader

There's a lot of talk about painting pavement white, but no mention of ripping it out and replacing cars with other forms of transportation. Internal combustion engine vehicles themselves turn 100% of the energy from gasoline into heat, localized to the roads they are driving on. This pumps billions of BTUs of heat directly into a city on a daily basis.[0] We could start cooling these cities down by not unnecessarily heating them up in the first place.

[0] https://www.treehugger.com/cars-add-heat-to-cities-ban-them-...

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Is there any evidence that the heat from cars directly contributes meaningfully to temperature in cities? I’m genuinely curious (but skeptical).

Edit: Some back of the envelope math:

Article says cars add 1.2 * 10^6 BTU of heat per day to Manhattan.

Some rough math on my part suggests that Manhattan gets about 5.6 * 10^11 BTU of heat per day from the sun, 5 orders of magnitude more. The heat directly generated by cars is a rounding error.

I always think it's kind of fun when we're reminded that the sun is literally a huge fusion explosion constantly going off in the sky. Using science to further appreciate the beauty of nature strikes me as very human.

The heat from vehicles isn't distributed spatially across rooftops/walls/trees where the heat might be dispersed; instead the heat from vehicles is concentrated and radiated adjacent to sidewalks (impacting pedestrians) and asphalt (which is effective at storing and re-radiating heat). Nor is it dispersed evenly throughout the day; congestion during rush hour will cause a spike of heat during the hottest part of the day with greater numbers of pedestrians experiencing that heat. Idling vehicles are also running air conditioning, and all of those idling/air conditioned vehicles will be creating an ambient atmosphere where their AC systems will have to run harder to create the same level of cooling.

As you note solar heating likely dominates the overall heating of the city but I would fully expect that idling vehicles contributes meaningfully to the pedestrian and driver perceptions of heat.

BS. Most cars drive on freeways and interstates most of the time, especially the large trucks etc. traffic in residential areas is generally pretty low and it more only during mornings and evenings.

This is just war on cars.

In a lot of US cities, freeways/state highways are where a lot of commercial, retail, and entertainment destinations exist. The first homes usually aren't that far away either, and a lot of apartment complexes are built directly on state highways.

Cars are used only 5% of the time, the rest of the day most of them sit around. They sit around in the sun, heat up and only disperse this heat during the night. Without those massive metal blocks in our streets, instead of large trees, the air could stay cooler during the day and night.

Indeed. And those pesky metal and concrete office buildings sit there empty half the time soaking up heat as well. Not to mention the apartment buildings.

In fact, let's just get rid of the whole city all together. That'll solve the problem.

Not sure how much heat is directly contributed by cars. But regarding the original comment, having dirt or vegetation will be less heat absorbing than even white or gray asphalt. Also it helps with runoff amongst other things.

Even if cars directly aren't contributing all that much, the amount of empty parking spaces likely make their direct surroundings less hospitable than whatever the natural vegetation would contribute.

Do cars cease to exist when they are not driven? No. They sit in a parking space, most likely in the open air where they take away space for trees. Cars is why cities heat up. Put them into expensive parking houses or underground parking to have more surface space for trees.

I'm specifically talking about heat directly generated by cars.

While the raw numbers might suggest that the heat from cars is negligible compared to solar radiation, that overlooks the Urban Heat Island (UHI) effect and the synergistic feedback loops that make urban areas hotter. The UHI effect shows that cities are warmer than their rural surroundings because of concentrated heat sources like cars, buildings, and human activities. This local heat really impacts urban microclimates.

Plus, the heat from cars creates feedback loops. More heat means more use of air conditioning, which releases even more heat exhaust, making the area even hotter. This cycle just keeps adding to the overall heat load in the city. So, even if the direct heat from cars seems minor on its own, it actually plays a significant role in making urban areas warmer.

I'm skeptical of that as well. It's my understanding that the Urban Heat Island effect is from roads and structures lowering albedo and absorbing more solar energy.

https://www.epa.gov/heatislands

https://www.heat.gov/pages/urban-heat-islands

https://www.annualreviews.org/content/journals/10.1146/annur...

A few of these do mention waste energy, but it seems to be a relatively small factor. And of waste energy, I would imagine that cars are themselves a somewhat small factor, compared to electric and natural gas usage.

The UHI effect is mostly down to solar radiation and the thermal mass of the built environment. The sun heats the concrete during the day which radiates heat at night, so that the next day the baseline is higher than the surrounding area. Cars and human activities are a drop in the bucket as a previous poster shows.

If Manhattan is getting 5.6 * 10^11 BTU of free heat energy every day, there isn't much of a reason to import more from outside.

You could lose 4 orders of magnitude to inefficiency and still have plenty to run your cars.

Almost nowhere in the American west has high enough population density to make public transportation very practical.

Sure, you could say "don't live like that". But in practice, that's saying to tear down and rebuild an absolutely massive amount of infrastructure.

On the other hand, if it gets too much hotter, a lot of people might leave, and the rebuilding project would get smaller...

Nonsense. There are multiple clear corridors that public transportation makes perfect sense for. A high-speed rail line from Fort Collins down south through Denver, to Colorado Springs, and potentially as far south as El Paso, seems obvious.

The Utah North-South corridor, as well. A line going from LA-LV-St.George-SLC area also makes enough sense. Not to mention a line connecting Tucson-Phx-Prescott-Las Vegas (potentially going to Reno as well). A Seattle-Portland train makes sense. A whole PCH line makes sense.

I'm not a fan of the high speed rail hype in the US. As another commenter pointed out, many cities are very suburban. So residents would have to drive to train stations just to get on in many cases.

That's ignoring all of the implementation costs, which would likely be extremely high.

> Internal combustion engine vehicles themselves turn 100% of the energy from gasoline into heat, localized to the roads they are driving on.

Let's consider a thought experiment.

We have an ICE car at the bottom of a hill. The car has a trailer attached and there is a weight on the trailer. The mass of the trailer and the weight combined is 500 kg.

The car is started, drives to the top of the hill which is an elevation gain of 100 m, drops off the trailer and weight, and drives back down to the bottom of the hill and is shut off.

The trailer and weight has gained 9.8 m/s^2 x 500 kg x 100 m = 490 000 J of gravitational potential energy, which is not heat.

If all of the energy from the car's gasoline became heat where did that 490 000 J of non-heat energy that the car gave the trailer and weight come from?

100% of the energy becomes heat eventually. For a typical trip, this happens by the trip conclusion. (And also each time the car pauses, such as a stoplight.)

For the trailer-on-hill example, it concludes when the trailer (eventually) is towed or rolls down the hill and comes to a rest from friction.

The weighted trailer is being used like a battery and modifies the situation in the same way as if it were a hybrid car (non-plug-in battery that recharges through regenerative braking and/or directly from the ICE).

If we are going to count energy that is delivered to the payload in a non-heat form that eventually becomes heat then yes, 100% of an ICE's energy from gas goes into heat--but so does 100% of an EV's energy or a bicycle's energy.

The difference between an ICE and an EV with similar sizes and shapes as far as heat goes is that although all the energy from both eventually ends up as heat the EV produces less unnecessary heat. To move the payload a given distance the ICE will use about 4 times as much energy. Only 1/4 of the energy from the gasoline goes toward accomplishing the job of the vehicle. The other 3/4 is waste heat.

Have you ever been to the American West? It's nearly all suburban. You would literally have to raze what's there and start over if you wanted to be able to efficiently transport people with public transport.

That would be sacrilegious to the American identity of requiring driving to do anything.

Why would anyone willing trade 2 12 minute drives to and from somewhere, anytime you want, immediately air conditioned, in the privacy and comfort of your own vehicle, with 2 32 minute dirty bus commutes that you have to plan in advance, walk to in the heat, and ride with other people-some of which are homeless.

What a stupid idea.

The stupid idea is believing public transit always implies longer and worse.

In most of the world where residential areas don't need highway-sized roads and you don't need 2 acres of parking lots for a grocery store, you can just walk for most activities.

Destinations are closed enough to your house that you can walk to the park or the bar. For activities that require hauling such as your groceries bikes tend to be enough. And for the people that do require a vehicle such as a work truck, there's so much less traffic on the road that it actually benefits them as well.

The issue is the US is stuck in a local minimum that is way worse than what's possible. They need cars because they build for cars because they need cars.

In reality you could _not_ need cars, because you don't build for cars, because you don't need cars.

The stupid idea is believing it isn't.

You can do the math in any major metro. The buses aren't driving faster than private vehicles. Worse yet, they have no privileges and actually obey traffic laws compared to normal traffic.

For all the years that treehugger readers and their like have espoused the benefits of no cars, it's like they can't do grade school arithmetic. No, it will always take longer to walk to public transportation, wait for the scheduled arrival, and walk to your destination in any existing metro if you don't give them extreme speed limit advantages that also put pedestrians at risk.

Go for it, be my guest, show me a single major metro in this American West as described by the article where you can alter the transit system to make things faster than driving your own private vehicle.

Oh you can't? It's because it's not possible. Oh, just build neighborhoods to not rely on cars from the start? Yeah, OK. Boy, isn't everyone just dying to not only finally own a house, but then own one where you can't drive anywhere and you're subject to the only grocery story in your area, along with everything else you're limited to walking to. What a wet dream for lack of competition.

Stupid idea.

The dumber idea is then these people say, "Well, not everyone needs to own a single-family home."

Hey, and while we're all at it, why don't all of us just own nothing, rely on public transportation, and rent forever. Or better yet, if we're all homeless, we can just have the government pay for everything.

No one talks about these things because they're pointless and add nothing to the conversation.

Worse yet, these people don't even give examples of where their supposed utopia already exists where there isn't an order of magnitude fewer housing units that you can actually own, businesses, or anything else meaningful you want to go to or have in your area.

The supposed answer is always denser housing, renting, and you not owning your own vehicle. Wow what a great standard of living! Sign me up!

Your comment is just very angrily agreeing with me.

Please note the main point of my comment, the US is _stuck_, they dug themselves into a pit where the only option is to dig deeper. That's the whole point!

> The buses aren't driving faster than private vehicles. Worse yet, they have no privileges and actually obey traffic laws compared to normal traffic.

That's because you build public transit that way, it doesn't have to.

> Boy, isn't everyone just dying to not only finally own a house, but then own one where you can't drive anywhere and you're subject to the only grocery story in your area.

You don't need a car, that doesn't mean it's illegal to own a car and drive to the next neighborhood. But since everyone around you doesn't need to get in the road for every little thing there's much less traffic.

> What a wet dream for lack of competition.

Lack of competition... because not having 50 parking spots per grocery store is _obviously_ anti-capitalist...

> Hey, and while we're all at it, why don't all of us just own nothing, rely on public transportation, and rent forever.

I don't know how you turned my comment into an argument against private property.

> Worse yet, these people don't even give examples of where their supposed utopia already exists where there isn't an order of magnitude fewer housing units that you can actually own, businesses, or anything else meaningful you want to go to or have in your area.

Again, I don't know how this is related to home ownership at all. You can still buy properties... And there are examples all around Europe.

> The supposed answer is always denser housing, renting, and you not owning your own vehicle. Wow what a great standard of living! Sign me up!

Again with the property ownership thing... Just buy your car, you can still drive to the corner store if you really want to, they'll just make fun of you.

How much heat to jets generate?

Meh. Why should we reduce our quality of life ? We can always use AC in cars and and at home.

All our energy usage turns to heat. Best to stay immobile.

The rich move to the city, the poor are squeezed out. The poor take long dreaded commutes that make them pay premiums for early/late daycare times and the long commute makes it difficult to find time to look for new jobs.

I make tons of money, I'd do great in your fantastic city. I stopped caring about the lower class last year. Your proposal is fine to me.

Just don't do a bunch of terrible bandaid things that mess up the economy in 20 years because you created a socioeconomic divide.

Because public transportation would be the enemy of the poor?

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