The purpose of this was to help students link the sentence of “can I take a ~ to the ~” with a, albeit weak, logical reason. I tried to design this so that the student would make the connection with the inability to take one of the learned modes of transportation with its apparent lack of service to the place the wanted to go to.
So if asked if one could take the bus to the bookstore the expected answer would be: “No, you can’t take the bus to the bookstore. Take a taxi,” with the reason being that the bus did not go out to that area of the city.
For some students it was easy to make the connection between the symbols and the ability of lack of ability to use the service, while other needed a bit more explanation. I never got around to redesigning this as I am no longer required to teach the concept of ability through this context.