Old hands at the metro

I have been impressed with how quickly the students, many of whom (I think) have never used a subway system, have adapted to using the metro as a primary means of transportation.  They have quickly learned the ins and outs of the system, and although there are a number of different mechanisms for getting in and out of trains, they seem to have mastered them without difficulty.  One of the curious things about the metro in Brussels is the system of elevators and stairs to the surface from the metro.  Generally when we approach an escalator it isn't moving.  We initially took this as a sign that the escalator was out of service, but when one of us got close enough to it the escalator immediately started up.  It's clear that the escalators here are on sensors to save power.  They don't operate until they are needed.  When a person approaches the escalator, though, the system starts moving and continues until everyone is off.  This is one of those innovations that seems obvious once you think about it, but I've never seen anything like it in the US.  I assume someone has done an analysis of the use of these escalators and has determined that it's more energy-efficient to start them up when they are needed rather than keeping them running all the time. 

Another interesting feature of the metro that I noticed today is something that I have not yet figured out.  This is a narrow track that runs down the center of the stairs into the metro.  It's a metal track with high sides and bumps along the bottom of the track to increase friction.  It's clearly not a drainage mechanism, because there are drains along the outsides of the stairs.  The walls of this track are too high for most luggage wheels to use.  The only thing I can think of is that it may facilitate the descent of wheelchairs.  This seems a bit unlikely to me, though, because it seems like the grade of most staircases is too steep for wheelchairs.  The track runs immediately to one side of the center handrail on the staircases, so it might be possible for someone in a wheelchair to use the handrail, but it seems awfully precarious.  The only other thing I could think of would be for bikes, but the track is close to the handrail, so it seems like handlebars or pedals would conflict with the handrail.  I'm kind of stumped by this one.  My best bet is for bikes, but even if you stood a bike up I'm not sure the pedals would clear the railing supports.  If anyone has any ideas, let me know.  If not, I'll see if I can find a Belgian to ask about it.

Mystery track down the stairs to the metro