Seperate from the FM transmitters that other people have mentioned, you can install an FM modulator into your car. This is a box that goes behind your stereo, feeds power off the stereo power supply, and connects directly to the antenna wire to supply the frequency modulated sound signal directly to the antenna without traveling through the air. Similar to an FM transmitter, it has a headphone wire that plugs into the headphone outlet of your ipod for the audio signal. It can bypass the interference problem that FM transmitters run into, but the one I installed back in the day actually picked up engine revving noise from my alternator, so maybe it needed better wire shielding. Obviously this requires taking out your stereo and doing some wiring work so you need some tinkering skills or have it installed by a pro.

The reason the USB plug on your ipod doesn’t work is that earlier audio devices like the original ipod didn’t have a way to transmit audio digitally over USB, it was only used for charging and file transfer.

Why not all three?