Germany’s oldest carmaker is making plans for a fleet of autonomous vehicles that customers can summon on demand, a response to the threat from Silicon Valley companies like Uber and Google that are pursuing their own driverless cars. Dieter Zetsche, the CEO of Mercedes-Benz’s parent company, Daimler, told Reuters that the robotic limousine is “a concrete development goal.” Daimler already owns Car2Go, a mobile car rental service, and has developed a futuristic self-driving Mercedes-Benz prototype.