Restrictions on validity
According to Downs, the link between average speeds on public transport and private transport applies only "to regions in which the vast majority of peak-hour commuting is done on rapid transit systems with separate rights of way. Central London is an example, since in 2001 around 85 percent of all morning peak-period commuters into that area used public transit (including 77 percent on separate rights of way) and only 11 percent used private cars. When peak-hour travel equilibrium has been reached between the subway system and the major commuting roads, then the travel time required for any given trip is roughly equal on both modes."[citation needed]
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So in general, it's entirely unclear whether this effect applies in most scenarios on the road network. In my area of NYC, a poster child for arguments about this effect and why we should never build anything due to "induced demand", it is vastly faster to drive across any borough other than Manhattan rather than taking public transit at all times except certain corridors at the absolute peak of rush hour.
If there were a proper subway line, running say from LGA, through Jackson Heights, Ridgewood and then cutting east through Brooklyn to JFK there's no way a driver could go faster on Grand Central Parkway anywhere near peak times.
The ones that aren't congested and have lower costs are smaller.
Unless you mean something else by "popular."
The only reason they don't rank at the very top is because they are in fairly low population density areas.
http://www.businessinsider.com/us-cities-with-most-traffic-2...
Commutes are also shorter. Average commutes in London is 74 minutes (round trip): https://www.thekingsferry.co.uk/industry-news/article/commut.... Houston and Dallas are 20-25 minutes less: https://www.houstonchronicle.com/news/houston-texas/houston/.... DC is the second worst in the US, and still about 10 minutes shorter than London: https://wtop.com/traffic/2017/04/dc-area-has-2nd-longest-ave...
And also it's only comparing very large cities in ~8 selected countries (no Paris or Rhine–Ruhr, for example).
(Source of your data, 2019 edition since I couldn't find 2017: http://www.demographia.com/dhi.pdf)
I don't think it's quite a fair comparison to compare that vs. Hong Kong or Singapore, especially when the London exurbs are called out separately.
I'd guess that NYC is in the same ballpark of unaffordability and congestion as London, but the deeper suburbs / exurbs of NYC are cheaper than their British equivalents.
I'd also wager that DC proper is cheaper than both NYC and London, both via absolute terms and income relative terms.
So if anything average commute should be longer because of all the people dragging their butts inside/out of the beltway every morning/evening.
1. Does that actually mean median 'house' price, or does it mean median 'home' price?
2. Is that price to buy, or rent, or what?
So, I think there's a few factors here. One is that recent booming usually leads to higher home prices, as the amount of building going on usually trails the number of jobs and income increases. It catches up eventually, but not until the boom stops.
The other is that it's true that sprawling out can decrease home prices. However, that tends to also increase transportation prices, since you're further out now. Americans spend a LOT on transportation because of the car dependency. Quick googling and math indicate annual household transportation spending of 9.7k for the US, 6.3k for Germany, 5k for Japan.