In Oslo, when a bus is reaching a stop, you can press the lower button to make sure the driver would open this door and, in case of having a baby trolley, press the upper one to ask him to wait a bit longer. The equation gets complicated when you realize that there is an additional red button for telling the driver to stop. In some cases there is also a button that tells the driver that an elderly person will leave. I guess that at the begining there was only the red stop button and others where added as an afterthought.
