There's an app that shows where the buses are in real time. For a backup, there are a lot of Uber drivers in Lowell.

Some locations in Lowell are very walkable and if you live in those locations, you don't need a car to survive. Besides sidewalks, there is a network of canal and river walkways in Downtown area that are practical for getting between points A and B. A car is a nice luxury for going to the beach and places like Great Brook Farm. There's ZipCar at Kennedy Center and a few other locations in Lowell. Put your street address in https://www.walkscore.com/ and see where your essentials are located. Try Commuter Rail for exploring Boston.

There are some dangerous intersections for pedestrians, but one learns to take a walking route that avoids the more dangerous intersections. 70% of drivers yield to pedestrians in crosswalks. 10% of drivers are dangerously distracted, so one must be careful. Don't wear headphones when you're walking around Lowell. Biking in Lowell IMHO is not practical and not very safe, though there are a lot of dedicated bikeways/trails for recreation in this part of the state.