Even with the best isolating headphones (around 25db; most non-IEM models offer much less isolation), you can still hear ambiant noises (unless your hearing is damaged to the point where isolating headphones do make you deaf). And with the standard set of Apple style headphones, they won't dampen the outside world at all.
Losing the ambiant noises will only occur when you overwhelm them out with your music, podcast, or navigation.
So the answer is, "yes." Not, "It depends on if you have ESP."
That said, some noise cancelling headphones offer modes that specifically let road noise through, and folks have hacked them to improve directionality of weak sound signals, and amplify voices. The Parrot Zik firmware comes stock with a 'street' mode.
It's entirely possible to have these systems function as hearing aides. MIT lab folks have demoed small wide-angle optical object detection that's then translated to directional feedback in a haptic belt.
Etymotic ER-4's are 35-42 dB; I've put mine in and not heard the bus zooming through the crossing I was about to stroll across…
ER4-XR's for me.
And running earbuds that loud for an extended period of time is a good way to lose your hearing.
Not all cars/phones/media can do handsfree.
However, what I do usually if I have to get directions just use my built in phone speakers.