If you want to use your iPhone Touch ID to unlock your car or for that matter any door that can be digitally locked and unlocked, soon you will be able to do so. According to this Mashable report, while Apple may not be directly working on developing a technology that would allow you to unlock your car using the technology used in your iPhone Touch ID system, one of its technologies may allow you to do that. Technology that allows your smartphone to unlock your car is already available for select car models.
Apple might not have been specifically working on a technology that would allow your iPhone Touch ID to unlock your car but it was the small part of the technology that would eventually allow your iPhone to drive your car. Rumours have it that Apple has been working on developing self-driving cars for long but somewhere it dropped the idea.