Most examples boil down to common sense. Nobody is going to arrest a 14 year old for driving their dying parent to the hospital.
Similarly, it is reprehensible but legal to pull up a chair and watch a child drown in a pool.
There is a difference between law and morality, and humans will use the second to selectively enforce the former.
In which country? Even for the US I don't believe the law system is that crappy.
In the case of a child in a pool, the difference is a matter of degree. What if I am terrified of water myself? Does that justify my inaction? What if I just "froze", which is common in stressful situations. Does anything justify not doing something?
For example, how fast can I drive to get to a telephone if I don't carry one or otherwise cannot use it?
Obviously not... If you have no means to communicate you are not required to communicate. I don't know why you'd think otherwise.
> For example, how fast can I drive to get to a telephone if I don't carry one or otherwise cannot use it?
This would obviously depend on circumstances and how safe you're able to drive without causing more incidents.
This is also why we have courts, and judges, and juries. They look at the totality of circumstances and arrive at judgement.