If you live in a large city — and more and more of us do, according to U.S. Census data — you know what a pain it is to own a car. It’s difficult to find parking, and when you do, it’s expensive. Insurance rates can be outrageous too. Taxis and ride-sharing services are an option, but you don’t know the stranger behind the wheel and those fares can add up quickly. By the end of the next decade, however, you’ll probably find that the cheapest, most convenient form of transportation is a shared, self-driving electric car, according to new research by the Boston Consulting Group.