How Do I Convince My Parents to get a Dog?

When I was really little, I used to tell my parents I wanted a dog even though I was afraid of them. Now, I'm a Junior in high school and I have come around to actually wanting one. My favorite breed is Boston terriers, so if I could get any breed it would be that. I've done a little research on Boston terriers, enough to know the basics about training them and they live 10-15 years. For me, it seems like the perfect dog. I'm an only child, my house itself is small, and I need something to motivate me to be more active but not so active that I don't have time for anything else. In my dreams, I see myself being totally devoted to this dog and loving every aspect of it. However, there are lots of problems that face me. To list a few, the street I live on is very busy, my house is messy and overloaded with random junk, I'm going to college in about a year, I've never owned a dog before, and this dog will be my greatest responsibility of my life so far. This doesn't even include how my parents feel about dogs. My mom is terrified of dogs, especially ones that are large and/or try to interact with her in aggressive kind of manor. She freaks out just when a dog touches her or barks. My dad feels that dogs are rather useless responsibilities that cause problems. He doesn't see the positives in many things, so he neglects all the good things about dogs that I've come to learn and want to have. I have more I want to say so I'm going to add it in the comments.