Close to motorways, adapted restrooms are usually available at the gas service stations, and when I'm in the city I usually look for department stores and McDonald's restaurants, which are required to have such a restroom. In the centre of Ljubljana, a restroom for the handicapped is in a bar called Global and in Nama department store. If you are travelling abroad, find out if subway is available in the city, as such transportation is very suitable (provided there are elevators available).