Is the subway a permitted walking route via an agreement then?What data are they hoping to collect? A few years ago bridge passes were issued and they could presumably see how many people were abusing it by how many passes didn't get handed in?
There's a similar situation at Ashford International with people using the subway to get from one side of the station to the other.
As for bridge passes, I know of people who ended up with bridge passes. Not because they were dodging the system but it might be that they were issued with one and by the time they go to the otherwise the passes were not being collected as the person wasn't there to collect them.
I'm not saying that was the biggest problem but it didn't happen.