Pros and Cons of Center- vs. Curb-Running Bus Rapid Transit


The City of Boston has created a pretty nice one-sheeter laying out the advantages, disadvantages, and design principles of running exclusive bus lanes in the center of a road vs. along the curb. As the Portland region considers BRT for future rapid transit lines (Powell/Division, Clackamas to Washington Square, and the SW Corridor are all under consideration for BRT), it is worth thinking about these principles and trade-offs, so take a look!

Center-running bus lanes in The Hague

In general, a center-running alignment is preferable if we want a high level of service. It eliminates conflicts with right-turning vehicles and bicycles, generally gives exclusive signal phasing for transit vehicles, and it breaks up wide streets in a way that can dramatically improve pedestrian crossings. There is a reason why virtually all transit (both trams and buses) in the Netherlands runs in the center of the street, and I can report from experience that it works very well and breaks up wide streets very nicely. Of course, we don’t have to look that far for examples. Our very own Yellow Line on Interstate and Blue Line on E Burnside follow the same principle, although I would argue they could be retro-fitted to be a lot more attractive.


Center-running transit can be quite attractive

Unfortunately, because Bus Rapid Transit is often chosen over Light Rail Transit as a way to save the most money possible on a project, it is all too often relegated to the outside lanes where performance is not as high. Both RapidRide in Seattle and Swift north of Seattle are examples of BRT lines that run in the curbside lanes, either in mixed traffic or in semi-exclusive Business Access Transit (BAT) lanes that are shared with right-turning and parking vehicles. While BAT lanes are better than nothing, they can often be just as clogged with cars as regular lanes, are difficult to enforce, and are often compromised (as we see through Interbay in Seattle) by making them peak-only.

As far as I can tell, there are two main reasons to choose curb-running over center-running lanes. First, if there is not enough right-of-way to fit in the center platforms. Second, if there is a political unwillingness to completely take away car travel lanes. The first reason doesn’t really apply to the roads being considered for BRT in Portland. Powell Blvd, even in inner SE Portland, has plenty of room to make the center lanes bus-only and still install median platforms. All we have to do is remove the center turn lane and the planted median. Same goes for Barbur Blvd in SW Portland, which has 3 car lanes in each direction and a small painted median.

The second reason is what will determine whether Portland ends up with high-quality BRT or not. People will object to removing any car capacity on Powell or Barbur, insisting they are critical auto corridors that should not be significantly altered. Curbside BAT lanes (probably peak-only) will be proposed as a way to “balance” the needs of cars and transit. ODOT continues to insist that Barbur needs its current capacity to act as an “overflow valve” for I-5 in case of accidents or congestion. These arguments fail to convince after the experience with N Interstate Ave. That was a road that was considered an important auto corridor and an overflow valve for the northern section of I-5, and yet we reduced its car capacity in favor of building MAX and life goes on. People have adjusted to the new reality and I am unaware of any major problems with the new configuration.

In the case of Powell, a reduction of lanes and a corresponding reduction in speeds would do wonders to improve the street’s safety, walkability, and livability. We should also remember that any BRT would be able to get off Powell somewhere around SE 17th to head up to the new Willamette transit bridge, so extra capacity would be available to deal with the Ross Island Bridge bottleneck. In the case of Barbur, that road is over-capacity anyway and should not be kept that way simply to absorb the occasional spillover from the freeway. Why do we have a 6-lane freeway and a 6-lane highway running parallel anyway? Rather than treating it as if it were one 12-lane superhighway in two parts, perhaps we should design them to perform distinct functions.

Zef Wagner is an analyst at Fregonese Associates and is pursuing a Master of Urban and Regional Planning degree at Portland State University, specializing in transportation planning. His views are his own and do not necessarily reflect the views of Fregonese or PSU.

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