Let me off of this bus!
October 25th, 2007 at 12:15 am
Ride the bus in San Francisco enough and you’ll see the following scenario play itself out over and over again. Just as the bus is about to speed away from the curb a cry will come from the back of the bus: “Back door! Back door!” Either the person wanting to exit is waiting for the doors to open automatically, or they’re pushing on them in vain. Whichever the case, they’re panicked, confused, and (rightly) convinced that any second now the bus is going to whip away from the stop without letting them off.
So what’s the problem? As tempting as it is to place the blame on clueless passengers, it’s really not their fault; there are several design issues that are conspiring against them.
Locked or unlocked?
While in motion the rear bus doors are locked and must be unlocked by the driver before they can be opened at each stop. There is a mirror mounted at the front of the bus that the driver can use see if anyone wants to exit through the rear doors, but frequently their view is blocked by people standing in the aisle, or they’re distracted by processing passengers entering the bus, of they’re in a hurry to try stay on schedule. For passengers, there is a green indicator light which illuminates once the driver has unlocked the doors however it’s mounted high above the rear doors in such a way that it is easily missed.
As a result, it’s no surprise that passengers end up on the rear stairs pushing on the doors while they’re still locked. The information passengers need in order to know whether or not the doors will open for them isn’t being presented in a sufficiently visible way and there’s no mechanism in place to relay feedback to the driver (short of yelling) when someone is beating on the doors unsuccessfully.
Magic doors
Another stealthier issue that trips passengers up has to do with the fact that not all doors on Muni work the same. Some buses require that you push on vertical bars mounted on the doors to open them, and people seem to understand this configuration well enough. In other buses, however, the doors lack push-bars and you must know to start descending the stairs while the doors are still closed; a pressure sensitive mat on the stairs causes them to magically open in front of you. These magic doors are problematic enough that the common cry from confused passengers (back door!) and the surly response from the driver (step down!) has become an in-joke among locals.
Muni’s magic doors suffer from a lack of perceived-affordances. Without bars or handles, passengers lack any obvious cues as to what to do in order to get the doors to open. (The large stickers inside the bus that warn “Do not stand in stairwell” in large red type can’t be helping either.) The designer or engineer may have felt that the design was both clever and efficient in the way it takes advantage of the action of exiting the bus, it turns out the design is just a bit too clever to be effective.
A modest suggestion
It’s my hope that incorporating the doors unlocked status light into the push-bars would make this crucial bit of information more visible to passengers by placing it in a position where their attention is likely to be focused as they prepare to exit the bus. Activating the green light within the translucent section of the push-bars could also serve as a prompt for action, uniting the knowledge that the doors are ready to be opened with an obvious affordance for doing so. To complete the communication loop, the driver should be notified, either by light or sound, when a passenger is pressing on the doors when they are locked.
Standardization across Muni’s vehicles would also be part of the plan. “Magic doors only” buses would have the new push-bars added, and the push-bars on Muni trains would also gain the integrated door status indicator. The clever mechanism behind Muni’s magic doors need not entirely be abandoned, it could be relegated to a secondary status, sensing when passengers are crossing the threshold and making sure the open doors don’t close on them as they step down.
Phew, who knew so much could be said about bus doors? The result of far too much time spent commuting on Muni and an urge to exercise my observation and design skills.