Sic transit gloria Bogotá

Bogotá is famous for its TransMilenio system. (I continue to confuse Bogotanos by referring it to it as the Metrobus, which is the name of Mexico City’s imitation.) TransMilenio is bus rapid transit (BRT): elevated stations with entry turnstyles and dedicated bus lanes. TransMilenio beats its Mexico City counterpart in having two lanes on some routes, allowing for express buses. I was last here in 2010; since then, the system has been extended east-west through downtown.

But it still, well, sucks. It’s overcrowded; always, all the time, sardine-overcrowded. And since the traffic lights don’t give it priority, it isn’t all that fast. It beats the smaller buses, and sometimes it beats a taxi, but it is not pleasant. Thus, angry riots in 2012.

The city is proposing a light rail system to supplement the TransMilenio. A surface tram would be cheaper than an underground metro, and trams have more capacity than buses. Sounds great! There are even private consortiums ready to cough up the money. So what’s not to like?

Simply put: light rail can’t handle the demand.

First, a bit about Bogotá’s geography. The city is sharply limited to the east by a large mountain range. The “Borde Oriental” sprawls north from the old downtown along the edge of the mountain range. Employment and (wealthy) housing has crowded along the Borde. (The Borde is traditionally held to end around 72nd Street, but has been creeping further north.) The city has then sprawled out to the west from the Borde. Imagine Chicago, only with a mountain range instead of a lake. Roads are numbered from the beginning of the mountains; each subsequent road runs is a little under 400 feet west of the previous, or about 50% longer than a Manhattan city block. Since the border of the mountain range is not really straight, Seventh Road is the easternmost road that runs continuously from downtown to the prosperous northern suburbs.

(This link gives a good overview, although the map inexplicably rotates the maps 90-degrees counterclockwise.)

Not surprisingly, then, one of the two proposed light rail routes runs north up Seventh Road from downtown all the way to 193rd Street. North of 119th Street it would transfer to an existing right-of-way, but south of there it would be right down the middle of Seventh Road. It is supposed to move 263,000 people per day at an average speed of 25 miles per hour. Trains will run every 2½ minutes.

Or not.

Each train will have a capacity of 760 people, cramming in ‘em at TransMilenio levels of six people per square meter of floorspace. (Try it: that is crowded. In fact, by the standards of everywhere save the Manhattan-bound F-train at 8:30am, that is overcrowded.) To meet the travel projections, peak demand will be 23,188 people per hour. At 760 people per train, that’s 31 trains per hour ... or one every 118 seconds. 118 is rather less than the projected headway of 150 seconds.

The traffic light at 72nd Street right now cycles at 120 seconds for cross-traffic. Keeping that would cut the number of trains per hour by a factor of three. Otherwise trains would back up at traffic lights and arrive in bunches ... the way buses always seem to. Moreover, cars often block-the-box: you would need to ban left turns, but even that might not suffice.

In fact, nowhere has at-grade light rail running at 25 mph with 150-second headways. Melbourne (unlike everywhere in the United States, including Philly and S.F.) kept its tram network after WW2. The most heavily used line runs at 10 miles per hour with a seven-minute headway. Not modern enough for you? Well, Paris is building a boatload of trams in its outer boroughs. They average 13 mph with a four-minute headway. (All data in the above is courtesy of Uniandes.)

Now, trams are a bit better than more TransMilenio lines. TransMilenio was always considered a second-best option, even by Mayor Enrique Peñalosa, who greenlighted it because the Metro was unaffordable at the time. But unless you can be assured that the private contractors will be picking up all of the capital cost, then it is far from clear that a light rail beats TransMilenio in cost-benefit terms.

A metro, though, clearly does beat both TransMilenio and the light rail. And design contracts were just signed.

But. The first problem is that a metro has a giant capital cost, and both the city of Bogotá and the national government are capital constrained. The second problem is that the city of is not, shall we say, well governed. Combine them and the privately-funded light rail line is going to be a hard thing to kill.

Which would not be terrible ... if you were sure that no public money would go into the light rail. Uh huh.