This year marks the 150th anniversary the world’s first subway, which opened in London in January 1863. Officially called the Underground, most Londoners refer to it as the Tube.

Today, subways are as popular as ever. Across the globe, from Cuiaba (Brazil), Mecca (Saudi Arabia) and Mumbai (India) to just about every major city in China, subway projects are well underway, about to start or deep in the planning stage. China takes up the lions-share of activity, with the government announcing last year 25 new subway projects worth tens of billions of dollars, according to the Associated Press. Beijing, the capital, has surpassed London and New York as having the world’s largest subway system and has announced plans to expand it still further to 1,000 kilometers by 2020.

The rapid pace of subway construction, especially in developing countries, has driven the number of systems in the world to more than 190, according to the Economist. One reason for the boom has to do with government stimulus programs that followed the financial crisis, allowing investment in subway construction to soar.

One country that’s noticeably absent from the project lists that appear in trade publications is the U.S. Construction of subways here, which the American Public Transportation Association defines as rail systems capable of handling heavy volumes of traffic at high speeds on separate rights-of-way, has slowed to a crawl. Washington, D.C.’s Metro was the country’s last fully-built rapid transit system in the country, with the final line of the originally planned system completed in 2001.

Since then, no city has expressed interest in building a comprehensive subway system, despite the fact there are five jurisdictions with a population over one million (Houston, Phoenix, San Antonio, San Diego and Dallas) that could be potential candidates. Instead, these cities and others, such as Denver, Minneapolis, Seattle and Portland, have opted to build light rail lines, which provide many public transit benefits, but are a far cry from the heavy volume, high speed, people-moving systems that rumble under the streets of New York, Chicago, Philadelphia, Boston and other major American metropolises.

What’s left is a smattering of active projects. After years of delay, Washington’s Metro has started construction of the Silver Line, which will connect Dulles Airport—the region’s major international air hub—with the suburbs of northern Virginia and, by extension, the rest of the subway system. The line’s 11.6 mile first-phase is scheduled to be completed later this year. In San Francisco, work has begun on something called the “Central Subway Project,” which is really a 1.7 mile tunnel that links one of the city’s light rail lines with BART, the region’s heavy rail subway system, which is adding an extension deeper into Silicon Valley that is expected to be operational in 2015.

The most heralded subway construction project to date is New York City’s 2nd Avenue line, which began in 2011 after decades of delay. Current work covers a 2-mile stretch under the east side of Manhattan that will have 3 stations. Plans are to build an 8.5 mile line that will run two-thirds the length of the island from Harlem to the financial district at the southern tip, but no funding has been committed for the entire subway line. The short section now under construction will cost a staggering $4.5 billion.

That figure, in a nutshell, is why there’s so little subway activity in the U.S. San Francisco’s Central Subway Project will cost $1.7 billion to cover less than 2 miles. Washington’s Silver Line is expected to cost $5.6 billion, but costs would have been even higher if plans to run certain portions of the line underground had been approved.

With transit funding still uncertain, given the lack of a stable, dependable funding stream from Congress, all but a handful of cities have decided to stay clear of such money-draining projects. But do subway projects have to be so costly? “Tunneling projects in New York routinely clock in at five to ten times the cost of their Asian and European counterparts,” according to Forbes.com, which added that U.S. built subway projects are three to four times more expensive than similar projects overseas. Governing columnist Alex Marshall has written numerous times about our unwillingness to invest in large-scale infrastructure projects, pointing to our “fragmented and incomplete approach” to how we do such work, which can drive up costs as well as impede plans to design and implement such projects.

Some might argue that we don’t need such large-scale transit systems, which are not only expensive to build but expensive to run. Indeed, debates over the pros and cons of a subway system have killed many plans while delaying some construction projects for decades, not just in the U.S. but in other countries as well. Still, we can’t ignore the fact that the U.S. is becoming an increasingly urbanized country, with more people working and living in cities every year. Subways provide one of the most efficient ways to move large numbers of people quickly, and they reduce pollution and congestion, which can negate the benefits of an urban society. That alone, especially for cities with populations of one million or more, is reason enough to give serious consideration to subway mass transit.

For evidence, one can take a look at the impact of Seoul, South Korea’s modern, well-run subway system. Here’s what Alex Marshall, who has done research in Seoul, wrote about it in Governing last year: “It is quite simply the best I have ever seen. The first line opened in 1974. Now, it has more than 10 lines and more than 350 stations. The subway has helped Seoul develop into a world-class city of 8 million and a metropolis of 20 million. Almost anywhere you want to go, it seems, you can go by subway. The total passenger ridership ranks second in the world [Tokyo is first], above New York City’s.”

Subways have a significant impact on the growth and success of today’s cities. It’s why the systems in Seoul, Shanghai, Beijing, Guangzhou and Bangalore have become such critical parts to their economic development in recent decades. It would be a big mistake for American cities to write off this valuable form of mass transit. We need to figure out how to make them affordable once again.