The United States is in the process of mandating an innovation commonly seen in Central Europe to guarantee train accessibility: the gap filler, also called the train-mounted extender. When there is a significant gap between the train and the platform, most passengers can still board fairly easily, but passengers who use wheelchairs may get stuck and passengers who have strollers, walkers, or heavy luggage may have difficulties. It is not always possible to reduce the gap to an acceptably narrow level, and therefore some trains have automatic gap fillers mounted on the train extending toward the platform.
What is the gap filler?
Here is a 10-second video of operations in Zurich. The gap filler is mounted on the train and extends over the platform, creating a continuous surface with gentle enough slope that people in wheelchairs can get on unaided. Without gap fillers, sometimes the train-platform gap is too wide and people can get stuck. If the gap gets wide enough, then even able-bodied passengers are at risk of falling through it.
There are also similar operations in Paris and various parts of Germany, though not Berlin. European railroads even use gap fillers when there is no level boarding, to prevent people from falling into the gap between the train and the platform, or to create an external step if the same train serves platforms with different heights one or two steps apart.
Why not just build trains with shorter gaps?
Train widths are not standardized in Europe – the loading gauge in theory permits trains to be 3.15 meter wide, but this is net of curves, so a rigid carbody always has to be somewhat narrower, especially if it is long. That by itself bakes in 10-15 cm gaps.
Two additional effects can create gaps. First, if the train platform is on a curve, then the distance between the most distant point on the train and the platform must increase even if the loading gauge is not defined on a curve. Second, wheels wear out over time, which may create a small vertical gap; if the vertical gap is more than about 2 centimeters then a substantial minority of wheelchair users can’t traverse it (see Barcelona’s universal accessibility plan, PDF-p. 14), and if it is more than 4.5 cm then a majority can’t. Even metro systems, which have level boarding, sometimes have big gaps because of these two effects, requiring manual bridge plates that lengthen station dwells.
Gaps and the United States
The American loading gauge is far more standardized than the European one, since the US is one country and Europe is not. Nonetheless, large gaps exist, for multiple reasons:
- The standards for platforms include generous margins: the distance between the track center and a high platform is by law 5′ 7″, and a train is at most 10′ 8″ wide (usually 10′ to 10′ 6″), so the laws already require gaps of at a minimum 3″ (76 mm, about the maximum passengers in wheelchairs can reliably cross) and often 4-7″ (10-18 cm).
- The American loading gauge is defined on straight track. Curved platforms require larger horizontal gaps, and as a result many agencies prefer not to build curved platforms at all, even where it is the best design compromise.
- There is some amount of oversize freight; the military wishes for a network with generous enough loading gauge to carry tanks.
Gap fillers were unfortunately unknown until recently. MassDOT even used the need for oversize freight as an excuse not to raise the platforms on commuter trains. Instead, American solutions included expensive gauntlet tracks or just keeping platforms low and inaccessible.
Fortunately, once an American implementation of the gap filler existed, namely on Brightline in South Florida, American regulators learned of the existence of this technology, and are now considering mandating it.
There are two conclusions from this story.
The first is that gap fillers are a good technology and more passenger railroads should use them to improve accessibility, not just for passengers in wheelchairs but also ones with strollers or luggage or who are at risk of falling through the gap. The US should aim for universal adoption of this technology nationwide.
The second is that once a good public transportation innovation does reach the United States, it can spread nationally more easily, as globally incurious but nationally curious administrators have a domestic example to look at. This is an example with train-mounted extenders, but the same may be said of fare integration, clockface timetables, lightweight EMUs, and so on. The first agency to adopt any such measure can expect visits from other agencies aiming to learn from its success.