US streetcar lines were in the 'transit death spiral' in no small part because they were largely built before cars were common, and became dramatically slower once car traffic started obstructing their right-of-way, which they were usually required by contract to maintain.

(There were many other factors, including their overexpansion during a securities bubble and that their concessions were usually for a 'nickel fare' with no inflation adjustment, which lead to declining real revenue over time)