According to the instrument rated private pilot, she was working toward a commercial certificate, conducting an instrument cross-country flight in VFR conditions with a safety pilot. During the final approach the airplane's altitude was low and she added power by moving the throttle but "nothing happened." The safety pilot in the right seat took the controls and made a forced landing on a highway. During the landing the airplane struck a vehicle. The private pilot and the safety pilot reported that they were not sure why the engine lost power. The private pilot reported that the accident flight was the second and return leg of the IFR cross-country flight. Additionally, the private pilot reported that the airplane had been "topped off" prior to the flight, which was about 181 nautical miles to their destination. During preflight for the return leg, she affirmed that she visually checked the fuel quantity in each tank and, "it was at the tabs". She completed a fuel sample and they departed for the return flight. According to the FAA Inspector that performed the post-accident airplane examination, during the examination, he observed that the fuel tank selector was set to the left tank. The fuel pump and carburetor float bowl had less than an ounce of fuel in each. The left wing tank did not contain any usable fuel and there was no sign of fuel on the ground post impact. The right tank contained about 12 gallons of fuel. According to the manufacturer's pilot operator handbook, per Chapter 3, the first step of the Engine Power Loss In Flight emergency procedure state: Fuel Selector…………………switch to tank containing fuel The airplane sustained substantial damage to the left wing spar.