。
I'm tired of riding in cars.
Literal
I [topic-は] automobile [in-に] ride [nominalizer-の] [target-に] am-tired-of.
飽きる (あきる, 'to tire of, get bored with') takes のに for the activity one is tired of. 自動車 is the formal word for automobile (more commonly 車 in casual speech). ~ている marks the ongoing state of being fed up.