Automobile design too contributes to mobility. The average family car today can run circles around the meanest muscle car of the 1950s. The combined mobility of streets and cars make ordinary drivers feel safe at roaring speeds, frequently exceeding 50 and even 60 mph on city streets.
Some would argue that speeding is a problem of enforcement, as posted speeds are being violated. However, when posted speeds are significantly lower than design speeds, law enforcement takes on the bait-and-switch air of entrapment.
All these automotive assets spell liabilities for pedestrians, especially now that studies demonstrate 37 mph to be the threshold for guaranteed pedestrian fatality. By contrast, speeds below 20 mph rarely result in serious injury. Other studies now link accidents directly to street width; as streets widen, fatalities increase exponentially.