Evidently tourists occasionally embark the incorrect BART train because of the aesthetic band of color located on the trains themselves. Specifically the Dublin/Pleasanton line which is designated with a blue color on the BART transit maps. All of the trains have this similar color on them which incorrectly leads an unfamiliar tourist to get on an unintended train.
This is a situation that describes unreliable, or misleading, signifiers. It sounds like these passengers are misinterpreting an aesthetic augmentation (the blue stripes), for a signifying label. I have ridden BART only a handful of times, and don’t entirely remember what the trains look like, but I would assume the stripes on the train are lacking sufficient differentiation from what [the passengers] are using as their conceptual model of the train line indicators. I would qualify this error as a mistake, and not just a slip, because of this fact—the passengers have an incorrect conceptual model of how the trains are labeled. It isn’t simply an action-based slip because, while the intention was to do one action, and another was performed, the one action was formed by an incorrect plan: get on the train with the blue in order to get on the Dublin/Pleasanton line. It also feels like what Don Norman calls a “knowledge-based mistake” (184), especially with the statement that those who most frequently have this confusion are “tourists”. These are people that, as he states, do not “have a good understanding of the situation,” Their conceptual model, of the familiar task of selecting and boarding their train, is incorrect in this new, novel, environment.
Applying a root cause analysis (perhaps in an opposite way), an accident might not be likely, but extrapolating the situation where someone needs to satisfy an emergency at a specific location on the Dublin/Pleasanton line, and thus missing the train to that location could result in an accident. Simply put, a missed appointment, could result in an accident.
Some quick design solutions might entail re-doing the aesthetic painted stripes on the trains to include all of the colors that represent the train lines. This may have the result of forcing the passengers to look elsewhere for the train demarkation, and dispel any assumptions. If all of BART’s line colors are represented, that might prevent the assumption outright. Another solution might involve better mapping on the actual train line map that these passengers would ordinarily use to choose their desired line. Perhaps the legend could include a representation of where to look on the actual train to determine which line it is. If the stripes were contoured in a way that drew the observer’s eyes upwards from knee-height to the train line’s destination sign/color. Associating each line with a different symbol would also better differentiate between them; this might also have the added benefit of aiding the color-blind. Including some form of feedback, like an audible notice of what train they have just entered may be helpful, although may result in more ignorable “noise” in the system.