Navigation company TomTom NV has discovered in the course of research for its traffic congestion index that German cities with the highest and fastest-growing apartment rents are also the most congested.
This finding contains an important message for city planners: instead of trying to fight cars, perhaps it's worth putting effort into building more housing and decentralising the business infrastructure to put people closer to their jobs.
TomTom found that Hamburg, the ninth most expensive German city for renters, is the most congested. Berlin and Stuttgart are in the top five in both rent levels and congestion. Munich, where apartments are the priciest, is the sixth most congested.
The company did this exercise only for Germany, but the global trend is obvious: the cities with the highest rents have the worst traffic problems.
TomTom's explanation is that in more expensive cities, people tend to move to the suburbs, where they can afford to live - but they still travel downtown for work.
"The disconnection of place of residence and workplace" plays an important role in traffic problems, the company wrote. Congestion, in other words, is at least to some extent rooted in inequality.
From a city planning point of view, the obvious way to reduce congestion (and the emissions it produces) is to get rid of cars, especially those that use fossil fuels.
Amsterdam, for example, intends to get all gasoline and diesel-powered cars off its streets by 2030, long before such vehicles are entirely out of the Dutch car fleet, which is, on average, more than nine years old today.
The measure looks progressive - but, especially in an old city like Amsterdam with a lot of activity in a single centre, it effectively penalises the poorer residents, who have had to move to the periphery, away from their jobs, and who can hardly afford new EVs.
Congestion pricing in cities and its extreme form - a ban on older, cheaper cars - deliver the not-too-subtle message that urban centres aren't for the poor. If you can't afford to live there, try not to come at all. Or use often inconvenient, overcrowded and underfunded public transportation, further lowering your living standards.
There are less painful ways of delivering the same message, such as trying to provide more employment opportunities closer to where those forced out of downtown live. Although an academic debate about the effectiveness of job and housing "co-location" has raged for years, some recent work shows that trying to make cities more polycentric works to cut commuting times and reduce congestion. (So, of course, does improving public transportation links to and from the multiple centres).
It doesn't, of course, work in isolation from other necessary efforts. Berlin, for example, has two centres left over from the time it was cut by a wall and an enviable public transportation network - yet it's Germany's second most congested city.
The steady rent increases keep pushing people outside the city, and many newcomers who find jobs in the capital settle outside its city limits, in the surrounding state of Brandenburg. In 2018, about 215,600 people commuted from Brandenburg to Berlin for work, 13.9 per cent more than in 2013.
Berlin traditionally has fought the trend by trying to control rents. By city ordinance, the price of a new rental agreement is linked to the area's average, big annual increases are banned, and there's a powerful movement against big landlords' attempts to get prices closer to the market level.
Rent controls, however, have long been known to economists to be far less efficient than new construction in pushing down housing prices. And, as instinctively as they want to ban cars, city administrators shun issuing more building permits. In Berlin, their number keeps dropping.
A city can reduce congestion and make the air cleaner through three parallel efforts: allowing as much housing construction as possible without overstraining the infrastructure, trying to decentralise employment and building up the public transportation network.
These efforts are relatively costly, and at times the construction and decentralisation parts may be unpopular. But pursuing them simultaneously is probably a fairer way to resolve congestion and air quality issues than artificially limiting poorer people's mobility.