Live traffic reports, even weather updates, are available on the navigation screens of many new cars. Turning a minivan into a roving Wi-Fi hot spot with Internet access for everyone on board is easy enough. Unlocking a car from 1,000 miles away is a simple task for a smartphone. But you still cannot watch broadcast TV on the road, or at least, it hasn’t been easy to do. That is about to change, giving relief to families and commuters trapped in snaking lines of taillights.