Sunday, September 16, 2012

The height (and length) of confusion

Tilting at Wheel Wells
Passengers like to lean against the front wheel wells on Metro Transit's buses, often despite open seats.

I found myself pleading my case to board a Metro Transit route 3A bus the other day. Classes were mostly wrapping up at the University of Minnesota, and I found myself as a random outsider among a crush of students who had collected along Pleasant Street as they waited to head home. I told the driver I needed to get to Hamline Avenue in Saint Paul, beyond the reach of the 3E and 3C buses coming up behind, and on a different branch than the 3B which was also sure to come before the next 3A. He grimaced but relented and let me board—I could have been stuck waiting another half-hour otherwise.

It has been rare for me to be told that a bus is too full for me to board, so I spent a moment wondering what was different this time. Soon I realized that I had boarded a standard, non-articulated bus with far less capacity than the "bendy" units I've become accustomed to on route 3. The extra room inside doesn't get used much in my own neighborhood, but passenger loads spike as the buses travel toward the University of Minnesota. If not for the heavy traffic near the university, the route would probably only use standard-sized buses 35 to 40 feet long, rather than the articulated ones which stretch close to 60 feet.

This reminded me of an open house I'd attended several months back where I'd gotten to talking with Metro Transit representatives about the pros and cons of the different bus types they have: Articulated, non-articulated, high-floor, and low-floor.

Some of the busiest lines in Minneapolis such as the 21 on Lake Street and the 5 on Chicago Avenue rely heavily—if not exclusively—on standard 40-footers. Some of the same lines also remain heavily-populated with high-floor buses where steps in always slow down the flow of boardings as many older and mobility-challenged riders try to ascend. While the ideal would seem to be a low-floor articulated unit because of the high capacity and relative ease of boarding, there are some drawbacks worth considering.

One of the biggest problems with urban mass transit is speed: Because of the large number of stops on bus routes and their poor maneuverability compared to cars, they can get dragged down to a snail's pace.  While articulated buses are great for improving capacity on a route, they tend to lengthen travel times because they can't accelerate or decelerate as quickly, and are harder to pull into traffic because of the larger size.  Over the course of a 40-minute route, an articulated bus could end up taking about 2 minutes longer (a slowdown of about 5%).

The huge accordion-like joint in the middle also has negative effects on handling—Occasionally, the buses can jackknife or spin out of control due to pendulum-like effects.  This usually isn't a problem in the hands of an experienced driver, but Metro Transit sometimes has to pull articulated buses off the roads as winter weather passes through.  Articulated buses are propelled by the single axle in the rear section, so the front end of a bus can easily end up sliding sideways on slippery hills.  (This is a significant contrast with light-rail vehicles and streetcars, which typically have several drive axles for traction and have rails to keep the vehicle segments aligned).

Artics still have important advantages, though: The greater seating capacity generally keeps the center aisle clearer, allowing more freedom of movement for passengers.  Dwell time (the time spent waiting for people to board and disembark at bus stops) is usually reduced or kept constant even with higher passenger loads.  The longer buses also tend to attract more riders (a modest instance of induced demand), apparently since some people are often turned off by the cramped quarters in smaller units.

Low-floor buses also have some interesting trade-offs: There's usually a reduction in seating capacity compared to high-floor buses, partly because the front wheel wells intrude into the cabin so much that it's impossible to place seats on top of them.  In some designs, there have been attempts to compensate by shaving off a corner of the wheel well to let people lean up against it more comfortably.  Unfortunately, that has turned out to be too comfortable—passengers can often be found hanging out up at the front of the bus despite plenty of open seats farther back.  This wouldn't be a problem except that there are more passengers getting on at other bus stops.  As people try to squeeze through, they get slowed down a lot, leading to lengthened dwell times.

For whatever reason, this appears to be a design fluke on Metro Transit's low-floor, non-articulated fleet.  The longer articulated units generally have squared-off wheel well covers, which seem to discourage that behavior.  The next-generation non-articulated bus that Metro Transit has been showing off this past week on route 10 uses those squared-off wheel wells, so hopefully the problem of crowded entryways will go away over the coming years.

Aside from that oddity, the case for low-floor buses seems to be much more clear: They reduce the need for lifts to be deployed for mobility-challenged riders.  No more steps to climb also means that anyone with poor knees or carrying heavy purchases also have an easier time when boarding.  There is a problem that the steps have simply shifted to the back of the bus—many riders are reluctant to climb them as the vehicle approaches crush loads, and calls by the driver for riders to move back often go unheeded.  I also personally find the ride to be a bit better on low-floor buses, with less rocking and rolling (I think the center of gravity is lower, or I'm at least closer to it when riding).

So, while it seems that a decision to go with a longer bus or a low-floor bus should be a no-brainer, there are a bunch of factors to consider.  Articulated buses in particular have been favored for bus rapid transit, but their poor handling really means that BRT has to be implemented with as few compromises as possible: They should have exclusive lanes more consistently, for instance.  And whether  implementing BRT or simply attempting to add capacity to an exsiting route, things like bulb outs, stop consolidation, removing unnecessary turns, and transit signal priority to give buses more green lights should all be considered to counteract the bigger vehicles' weaknesses.  In some cases, shorter buses turn out to be the better option.


  1. Fort Collins, CO, uses NABI 40-LFWs for most of their routes, and I tend to notice the same thing. For one, people are reluctant to sit next to one another in the forward-facing seats on the local routes, preferring to stand if they are only going a short distance. The rear door is also a popular place to stand, though it works out alright for passenger flows because of the wide rear doors. Personally, I would like to see all of the seats in the low-floor section rotated to face the aisle, in order to create more standing room space.

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