IF Mercedes, BMW and Ford have their way, the new cars they build will be able to port apps, games, music and movies from a smartphone to a car’s entertainment system. But for every potential distraction automakers add, they find themselves having to build in ways to prevent drivers from crashing their new smartphone on wheels: automatically applying the brakes at a traffic light; alerting drivers when a car is in the blind spot, or reading traffic signs and slowing a car as speed zones change. “We can’t stop the prolific growth of consumer technology,” said Paul Mascarenas, chief technical officer at Ford. “We can’t stop people bringing phones in their cars. We endeavor to make sure people do it in the safest way possible.” Ford’s Sync App Link, Mercedes-Benz’s forthcoming DriveStyle app and BMW ConnectedDrive have slight differences in execution, but the purpose is the same: importing apps and content from a smartphone into the car’s displays and controls. Using the smartphone as a hub of digital content and services means drivers are able to preserve the same media and features they use when they are out of their cars. “You’re already used to using your phone,” Mr. Mascarenas said. “We’re trying to create a seamless experience from your home or office into your car.” Today’s cars already can do many automated safety tasks. The typical car can require seven years or more of development. Designs and specifications are fixed years before the first vehicle rolls down the assembly line. By making the smartphone a component of the car, automakers hope to hitch a ride on a technology that changes in months, not years.