Flickr user adrimcm under a creative commons license

As Istanbul awaits the completion of its trunk subway line, the Metrobus has performed admirably.

When a new metro line opened up in Istanbul a couple weeks ago, it mostly served as a reminder of something the city has been awaiting for the better part of a decade. That would be the massive Marmaray project, a rail tunnel beneath the Bosphorous strait that will link the European and Asian sides of the intercontinental city. The delays have been reasonable — crews have had to deal with tricky geography, safety precautions required by a nearby fault line, and archeological discoveries made during the digging — but the initial phase is still a year from opening, and the full deal several more.

The city wisely recognized that the immediacy of its traffic problem demanded some sort of short-term solution. Its response was to lay down, within a couple of years, a bus-rapid transit system known as the Metrobus. The 26-mile line operates in dedicated lanes along the D-100 expressway and connects both sides of the city across the Bosphorous Bridge. By most measures it's been a great success, according to a recent profile of the system in the Journal of Transport Geography.

For starters, it's pretty fast. Except on the bridge, where it enters mixed traffic, Metrobus nears speeds of 50 miles an hour and completes its entire route in about 60 minutes. That's at least twice as fast as cars travel in the corridor, and also considerably faster than the previous bus and ferry system. It's also convenient: an estimated 10 percent of the entire metro population lives within a 10-minute walk of the nearest station.

The frequency is almost ceaseless. High-capacity Mercedes buses, which can fit up to 200 passengers at a time, arrive every 30 seconds during rush hour on the European side (and every 45 seconds at the bridge crossing). During morning peak, ridership tops 30,000 each way, and the system as a whole serves more than 620,000 passengers a day. EMBARQ puts the total figure much higher. Still the bus is crowded; it's not unusual for waiting passengers to board the third bus they see.

The city's mayor, Kadir Topbaş, recently noted that with the numbers being handled by the Metrobus, the corridor should have a light rail system of its own. Evidently the bridge over the city's Golden Horn inlet can't accommodate rail, so instead Topbaş is proposing a plan that attaches the buses together, so they form a sort of "metrobus-train." With frequencies already so close together, it's hard to see how that idea would do anything but waste some rope.

Istanbul isn't the first city to try BRT as a transit band-aid and realize what it really needed was a suture. Ottawa recently went through a similar experience with its own BRT system. The city proposed a (Canadian) $2.1 billion light rail to increase capacity — a project so expensive that transit writer Yonah Freemark wondered if it wouldn't have been more fiscally prudent to choose light rail from the start. "For other cities considering investing in reserved-bus corridors before light rail, Ottawa’s may be a cautionary tale," he wrote.

Still, if Istanbul dismissed such a caution, it would be hard to fault the city. For starters, it didn't need BRT to prove the value of mass transit. Ottawa's BRT showed that transit could capture a quarter of the city's transportation share, but in Istanbul, that figure is now 50 percent, and was high even under the old system of slower buses. Meanwhile the city had already decided to invest heavily in the Marmaray project, which is estimated to cost up to (American) $3 billion.

Rather, Istanbul's major concern moving forward should be getting people off its enormously congested roads. Public transit has half the city's transportation share, yes, but only 4 percent of that share belongs to rail. The completion of Marmaray, and its connection to the existing metro, light rail, and Metrobus lines, is expected to boost rail ridership closer to a quarter of all transit — that's a big cultural change. To date, only 9 percent of Metrobus riders have shifted to the mode from car use, as many as shifted there from trains.

The real cautionary tale of Istanbul may be the way it handled highways to make way for the Metrobus. It did give the system dedicated lanes throughout the corridor (except for the bridge), but it did so by narrowing — as opposed to removing — other lanes. That created loads of induced demand, as the old buses left the mixed lanes, inviting more cars onto the squished highways. And by refusing to make room for a dedicated BRT lane, the bridge authorities further increased congestion, decreased BRT efficiency, and perpetuated the city's road-first mindset.

Istanbul seems to have successfully weathered a tough era of congestion by implementing BRT as a transition to rail. Soon it will have the high-capacity trunk rail line that's long been needed. The city's next challenge will be making sure people get off the roads and use it.

Main image: Flickr user adrimcm under a creative commons license; inset, P. Alpkokin & M. Ergun. Istanbul Metrobüs: first intercontinental bus rapid transit. Journal of Transport Geography, 24 (Sept 2012), pp. 58-66.

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