Increasingly, we’re talking not just about metropolitan areas but about megaregions. The America 2050 initiative explains:

As metropolitan regions continued to expand throughout the second half of the 20th century their boundaries began to blur, creating a new scale of geography now known as the megaregion. Interlocking economic systems, shared natural resources and ecosystems, and common transportation systems link these population centers together.

Those economic links lead to travel. A megaregion needs a megaregional transportation network. We have megareigonal highways and megaregional airlines. We also need to be thinking about megaregional transit.

This is by now means a novel thought. A linked megaregional transit network is taken for granted in Britain, Japan, and most of the world’s industrialized countries. The German railway actually offers a trip planner for the entire country: any bus, light rail, subway, commuter rail, or regional rail stop in the country to any other.

We had this kind of network in the United States once, too. We let much of it disappear, and the rest has been divvied up by a confusing array of local, regional, statewide, and national agencies. The separation between Amtrak and commuter rail, for example, is arbitrary: commuters can ride Amtrak and intercity travelers can ride commuter rail. But federal law distinguishes between the two. The result is a fragmented network, one that can be hard to comprehend in its totality.

But now that we are talking about high speed rail, our existing networks become relevant. High speed rail wants feeders. Some riders will arrive by car and depart by taxi, but there’s no doubt that good local and regional transit connections make megareigonal high speed rail more relevant. And, make no mistake, high speed rail is an interregional mode. It’s cities less than 3 hours — 600 miles or so — apart where high speed rail is most effective. Houston to Dallas makes sense. Houston to Chicago doesn’t.

So let’s take inventory.

The closest the United States gets to megareigonal transit is in the Northeast. Amtrak’s Northeast Corridor, the fastest railroad in the Western Hemisphere, links Boston to New York to Philadelphia to Baltimore to Washington. The Amtrak station in each of those cities is also a commuter rail hub and is connected to an extensive urban rail system. This network befits a region that is still the densest in the United States and the most prosperous: 4 of the 10 largest metropilitan areas and 8 of the 10 states with the highest per capita GDP are in the the Northeast.

On this map, black lines are Amtrak routes and red lines are commuter rail routes. The thickness (and the little italic numbers) indicate trains per day. Orange dots are major cities with local rail transit systems; white dots are major cities served by regional rail without local rail. Of course, not all cities are created equal, so the grey circles indicate metropolitan area size: the area of each circle is proportional to population. All these maps are to the same scale.

Those dense red bundles are eight of the ten busiest commuter rail systems in the country. This is the heavy-duty infrastructure I talked about last time. Boston has two stations with 183 and 378 commuter trains a day, respectively; New York gets 529 commuter trains a day at Grand Central, 734 trains a day (and 150 Amtrak trains) at Penn Station, 286 trains a day at Hoboken, and 145 trains a day at Flatbush; Philadelphia gets 458 commuter trains a day through its downtown spine, Baltimore sees 95 trains a day at two stations, and Washington Union Station sees 115 commuter trains a day. Those systems carry 1.2 million people a day, 4 times as many as Amtrak does in the same region. But that’s nothing compared to the local transit: the New York Subway alone carries 7.6 million.

The coherent spine of this system is Amtrak’s Northeast Corridor: nearly 100 long-distance trains a day on up to 4 electrified tracks. It connects the old port cities that have been the economic engines of this area since colonial times. It has literally defined this region. But you don’t have to go far inland to find a completely different world. The struggling Rust Belt towns in the inland valleys see little or no rail service. There are frequent Amtrak routes to Hartford, Harrisburg, and Albany. But beyond there, frequency falls off, often to only one daily train in each direction. Cities like Scranton and Reading have no service at all.

The region that seems closest to new high speed rail service is California. Despite the state budget crisis, planning moves ahead to link San Francisco with Sacramento. California is not as populous as the Northeast, and the cities are further apart. But you have the 2nd and 6th largest metropolitan areas on each end and a string of cities in the Central Valley between Sacramento and Bakersfield — a ready-made corridor. Moreover, California’s been building a lot of local transit and laying the groundwork for high speed rail with regular speed rail: state-funded Amtrak corridors from the Bay Area to Sacramento, from the Bay Area to Bakersfield, and from San Luis Obispo through Los Angeles to San Diego are the busiest Amtrak routes outside the Northeast. Californians are getting used to thinking of train travel, and that makes high speed rail an easier sell.

We have left the land of first generation commuter rail behind, with the exception of San Francisco to San Jose’s Caltrain. Commuter rail service is much less frequent than it is in the Northeast, and these systems carry a lot fewer riders, too.

Up the Pacific Coast, Oregon and Washington, the 13th and 27th most populous states, seem unlikely high speed rail candidates. But much of that population is in a narrow strip along the coast, and in the 1990s the two states partnered to buy tilting Talgo trains that can make 80 mph (110 with track upgrades) on a curvy route. Portland and Vancouver have long had good local rail systems, and Seattle is getting its act together, too. The topography makes 250 mph high speed rail prohibitively expensive. But continued expansion of medium-speed rail service seems likely.

Chicago is the third largest metro area in the country, with arguably the second best rail transit network. But the rest of the Midwest pales by comparison: Detroit is #12 and sinking, Minneapolis is #15, St. Louis #19. A lot of the population is spread out across the prairie, in a series of 200,000 to 600,000 metro areas.

Chicago has been a railroad hub for 150 years; it’s no surprise it has a major commuter rail network and Amtrak routes in every direction. But overall, the Midwest rail network is poor. The rail lines were built across the prairie towards distant destinations, and they missed many of the smaller population centers. Illinois funds three Amtrak lines, but the third, fourth, and fifth largest metro in the state are unconnected. Indiana and Wisconsin, which don’t fund service, are even worse: the state capitol and college town of Madison, WI is an obvious candidate for a rail connection to Milwaukee and Chicago, but today you have to take a bus.

The Midwest has been planning 110 mph rail for over a decade. In a flat landscape crisscrossed with active and inactive rail rights of way, that’s not technically difficult. The problem is getting seven states to agree on anything. So far, the only fruits of that work have been some basic track upgrades. For a few miles across southern Michigan, Amtrak actually goes 110 mph already. But then it has to get in line behind freight trains again.

So where’s Texas? The Amtrak network is pathetic, to put it mildly. The busy routes are two trains a day (one in each direction); Houston gets 0.9 (three trains a week in each direction.) The Texarkana-San Antonio and Beaumont-El Paso routes are long-distance trains, so they come through at odd hours and are likely to be late. Fort Worth-Oklahoma City is state-funded corridor service, so it’s better, but it’s still only one round trip daily. You can take a day trip from Oklahoma City to Fort Worth, but not vice-versa. The local transit picture is getting better: Dallas and Houston have successful local rail systems. But San Antonio doesn’t have a local rail system, and Austin is about to open a stupid one.

But here’s what Texas does have: the #7, #9, #29, and #39 metro areas within 300 miles of each other with a big flat plain in between. And it’s all in one state, so if that state government got behind rail, it could happen pretty easily.

Ultimately, high speed rail can’t been seen in isolation. Every country that’s built high speed rail added it to a system of urban rail transit, regional commuter rail, and regular-speed intercity rail. It’s going to be easiest to make high speed rail happen where some of that network already exists. But where that network doesn’t exist, this is the time to build it.