> Could someone explain to me why cars running on natural gas aren't popular in the US like they are in South America / Europe?

There are many fleets which use natural gas. Municipal buses, city garbage trucks, etc. There, they only need to build up one (private) CNG refueling station in the city.

With a passenger car, you need to plan your trip to find public CNG fueling stations along the route where you need them.

The boom in natural gas production is a recent occurrence. Go back a couple decades and natural gas was far more expensive. Back then, propane was the obvious alternative to gasoline for vehicles, until the price for propane spiked and natural gas fell.

But more importantly, CNG is only a half-step forward, still leaving us dependent on a single fossil fuel. Battery electric vehicles are far more practical thanks to being easy to (slow-)charge almost anywhere, getting us off of fossil fuels entirely, reducing mechanical complexity/maintenance, and being far more efficient (burning the same amount of natural gas in a power plant to charge your BEV will give you far more range than burning it in your converted car engine).

There are a number of issues:

- First of all, there is no natural gas fuel standard

- Safety, there are no safety standards. If there were, tanks often used in other places, such an upgraded would be more expensive

- Rolling out refueling over the whole of the US/Europe would be difficult. Most places in Europe don't have these cars.

A better and safer alternative to natural gas would be methanol. And because of the US ethanol policy, the US already has a surprising amount of Flex Fuel Vehicles.

If you could have a bunch of fuel standards for ethanol/methanol and a vehicle standard for those fuels, depending on the price, people could buy different mixes.

Converting gas to methanol is fairly efficient and can be done directly at gas production sites, sometimes with gas that would be vented instead. But there isn't a big market for methanol right now.

In China such standards do exist M20 and so on. However sadly there methanol vehicles usually use methanol made by coal.

The US would have had much lower fuel cost if they had a strategy of methanol and ethanol at the same time, and require all vehicle to be FFV. Standardizing M20/E20, M50/E50 fuels for example.

However all of this is now no longer very useful as car market is rapidly switching to electric.

For some trucks using generated fuel might be useful. Dimethyl ether would be great for long range trucks and ships rather then hydrogen.

On lose power and internal space on the conversion.

The US car market does not seem very concerned with economical ROI, so any argument based on costs is useless. The emissions part seems to hold for some people, but electric cars already won here.

Even here on South America gas is getting out of fashion, replaced by electricity. The costs are still high enough that there is a large market remaining, but it is constantly decreasing.

There are not enough places to fill a natural gas car. I know of a few, if you buy a natural gas car you plan all trips around filling up - and a lot of trips you have to reject.

For every public natural gas pump I know of, I know of 50 public EV chargers. Plus in the worst case you can plug an EV into a regular outlet (overnight you can get enough range to get someplace with a faster charger).

I'm no expert but I think when cars are converted, they can run on both natural gas and on gasoline. Gasoline is used to start the car. Wouldn't that solve the range issue?

Obvious problem in USA is availability of natural gas at gas stations, but that is a chicken and an egg problem - would be solved with more demand.

natural gas emissions are not less harmful

Can you explain your reasoning? There are a number of reasons that natural gas emissions (after burning) are less harmful. Not least that there is a higher proportion of hydrogen so for a given energy output there are less carbon dioxide emissions.

Methane emissions from incomplete burning, and also from upstream.

Methane emissions are an issue with basically all uses of gas that has been underestimated in the past and only in recent years it's more widely recognized how problematic that is. A lot of the "gas is greener than X" messaging from the past is simply no longer true if you consider methane emissions.

Methane emissions from oil extraction aren't negligible either so it depends on your point of reference. It's almost certainly better to burn methane in a power plant and use BEVs where possible but that's a long way from possible in heavy goods vehicles for example (they will need batteries measured in MWh for a start).

There are also many dimensions to emissions, global warming potential is important but from a personal point of view I worry more about the impact on my children's health from the other emissions like particulates, NOx and aromatic hydrocarbons.

but they are less. You can half the co2 emissions with very little investment. However, this cannot be ultimate solution and is probably too little too late.

Not true, there's way less NOX and particulates, all the stuff that's bad for people in urban environments.