Is it normal that my mother doesn't let me outside alone?

I am 18 years old, and my mom doesn't let me outside of the house alone anymore. Whenever I ask her why, she just tells me that "she's worried" or something. I don't live in a particularly dangerous area, and when I was younger, I used to be allowed out alone almost whenever I wanted, as long as I didn't go too far. But nowadays I can't even go to the store that's a 5 minute walk from my house on my own. When I try to leave, she asks if she can come with, and if I say no, she pleads with me until I finally cave. She's also home all the time, so sneaking out isn't really an option. Is it normal that she does this? If not, is there anything I can do to finally get out? I feel trapped with her by my side out there. I miss taking long walks by myself.