Is there someone that has knowledge on hours of service, specifically on the 16 hour exception?

I was told that it can be used once a week or after 34 hour reset, for the purpose of EMERGENCIES, BREAKDOWN, WEATHER. also heard that traffic was in there also. and that the driver must be enroute to his domicile, not working.

I've also heard that he can be working.

This question is mostly concerning local pu&d.

If someone knows the official law on this, it would be appreciated.
Also, any links to the specific's would be great.

I have searched the dot sites, but have found no specifics. If this is really open to interpretation, then, this is messed up.

Thanks