Passenger numbers more the doubled in the last 20years. The biggest one is regional transport, which already uses double decker trains in most cases. So to increase capacity you need to make them longer. That however requires longer platforms as well.
Also if you want to change trains, the operator is generally trying to have different trains arrive and leave at roughly the same time, so passengers do not have to wait too long. Obviously that means you need the tracks for that as well.
Passenger numbers more the doubled in the last 20years. The biggest one is regional transport, which already uses double decker trains in most cases. So to increase capacity you need to make them longer. That however requires longer platforms as well.
Also if you want to change trains, the operator is generally trying to have different trains arrive and leave at roughly the same time, so passengers do not have to wait too long. Obviously that means you need the tracks for that as well.