There have been a lot of bumps in the road for startups building used-car marketplaces, but now one of the longer-standing of them has closed a major round of funding — a clear sign of the mileage left in this category. Vroom has raised $254 million, a Series H that it plans to use to keep scaling the business, and specifically also to expand a product and engineering hub based out of Detroit. Vroom is based out of New York but operates across the US, and its platform has to date been used by more than 250,000 buyers and sellers, according to the company.