I often come to visit my grandparents during the weekend and they will always come to fetch me at the train station in their car.
However, my grandpa (who is the one driving) is old and his vision has deteriorated a lot lately. He can still drive but I don't feel safe with him doing so. I would rather have both of them stay at home and walk to their house (it's not that far and it's also better for the environment).
So, I would like to ask my grandparents to not fetch me at the train station next time, but I'm afraid they will take it badly (as in: "hey, you are such a bad driver I'd rather walk").
So, is there a tactful way I can ask them to not come?
Notes and clarifications
My grandpa doesn't like driving very much. However, I don't want to risk hurting his feelings.
Walking to come to fetch me wouldn't be possible for my grandma, and my grandpa really doesn't like walking (and I don't want to cause them trouble since walking alone from the train station to their home is really not a big deal for me).
I don't consider lying to be an acceptable solution.
Some solutions suggest not to use the real reason as to why I don't want them to come. It's an option but I am even more interested in being able to say nicely to them "don't drive me because I don't trust your driving ability anymore" (when to talk about it, with who involve, etc.).
I consider driving to be a dangerous activity no matter what. And that driving with a bad vision is even worse. So I want to communicate something like "I don't want you to take risk driving (with your bad vision) when I could easily be walking"
I probably should have said this sooner, but I'm not really athletic and if I say to my grandparents "Don't come fetch me because I like walking", they will probably not believe me.