[tz] Oregon to join remainder of US West Coast with permanent DST?

Paul Eggert eggert at cs.ucla.edu
Fri Jun 7 19:38:57 UTC 2019

On 6/7/19 11:57 AM, Paul Gilmartin via tz wrote:
> States may likewise choose to move one timezone eastward.  Either action
> requires only approval by the Secretary of Transportation, not an act
> of Congress.
The Secretary's authority to do that is not unlimited. Changes to time 
zone boundaries by the Secretary must have "regard for the convenience 
of commerce and the existing junction points and division points of 
common carriers engaged in interstate or foreign commerce" according to 
the US Code. The DOT's website for this 
suggests that they probably wouldn't approve the request of a whole 
state merely on the grounds that the state wants to change. My guess is 
that this is because such a change could be challenged in court on the 
grounds that the confusion would hurt commerce and thus contradict the law.

> What is the effect on tm_isdst?  Do they care whether their documents
> are timestamped PDT or MST?

As far as I know these questions have not been addressed, and quite 
possibly they won't be addressed even if the law changes so we'll just 
have to do our best. If (say) California changes to permanent -07 then 
the longstanding tzdb tradition would be to mark it as standard time 
(i.e., tm_isdst = 0); presumably it would be abbreviated "MST" for 
compatibility with Internet RFC 5322 and the like. No matter what we put 
into tzdb at that point, we'd undoubtedly break something and get 

There are similar issues in the upcoming changes to European time zones.

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