Microsoft Streets and Trips information

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Exceptions, Oddities and Notes

A word about standards. All time zones world wide are based on offset from the Prime Meridian, also known as the Greenwich Meridian. That is the line that runs from the north to the south pole at longitude 0°. No matter what you call it, it passes through the Royal Observatory in Greenwich, England. Thus "Greenwich Mean Time".

In research literature and in cyberspace you will find Greenwich Mean Time referred to in many different ways, usually GMT, UTC (Coordinated Universal Time), or Zulu time. Military and Aviation usually use Zulu, or just Z.

Here at we use GMT, because that is what travelers seem most familiar with. Time geeks (they walk among us) will prefer you use UTC when conversing on the time related topics. And truly there are small technical differences between UTC and GMT, but travelers need not concern themselves about it.

Time zones are fundamentally based on 24 imaginary wedges running from pole to pole at 15 degree increments, beginning centered on longitude 0°. Starting with an offset of zero hours for that first "slice" (which occupies the longitude from -7.5° to +7.5°) heading eastward, for each 15° wedge you add 1 hour for each zone, and heading westward you subtract 1 hour for each zone. They meet on the other side of the globe at the fundamental basis of the International Date Line, the imaginary line that runs from pole to pole at the 180° longitude.

In reality, actual time zone lines deviate (often radically) from their fundamental basis. Politics, history, commerce, and sometimes forces that defy rational explanation all combine to influence the real time zone borders.

The International Date Line itself is similarly influenced, following a ragged path roughly centered at 180° longitude. Crossing it traveling eastward you subtract 24 hours, and if traveling westward you add 24 hours. Simple :)

Most time zones are offset from GMT in whole 1-hour increments. A few offset from GMT in fractions of an hour -- most of those by half hour, a few by a quarter of an hour.

Forward thinkers want to end the madness. Click here to see their their elegant solution.

There are 9 time zones in North America. Being in the Western hemisphere, they are offset from GMT in negative increments:

  Hawaiian/Aleutian Alaska Pacific Mountain Central Eastern Atlantic Newfoundland Pierre
Standard Time


-3:30 (really)
Daylight Saving Time



-2:30 (I swear)

Understanding exceptions

Where locally "observed" time differs from official, the main borders in follow the observed time - which is what a traveler is likely to actually encounter.

A problem with that is that unofficial "observed" differences usually follow vague areas of economic or political influence which defy precise definition. But we had to draw them somewhere. Usually these borders are in very lightly settled areas - and we took pains to draw them on the correct side of any area which may have businesses, services or significant population. That was our intent anyway - corrections appreciated!

Wherever these areas are in the US, unofficial borders are drawn in lime green, with the official alternative drawn in dark green. No attempt was made to do this for other countries, because distinctions between official and unofficial blur a bit in the various political subdivisions. In the US all official time zone borders are well and clearly documented by a single source - the US Dept. of Transportation.

But be aware that within an area where observed practice differs from official, there are often internal exceptions. Possible examples are polling places, post offices or other federal offices -- and sometimes law enforcement or various other governmental entities. These may observe official time even if the rest of the community does not.

Bars or liquor stores in these areas are often required by law to observe official time. This can provide quite an advantage for properly situated bars, when last-call sojourners migrate across an official time zone border to cadge one more hour of bliss.

Here are the exceptions that made their way into the boundaries at


NV: In northern Elko County Nevada Jackpot, Jarbidge, Owyhee, Mountain City, and the Duck Valley Indian Reservation all observe Mountain time though they are officially in the Pacific time zone.

NV: West Wendover Nevada is officially in the Mountain Time zone.

OK: Kenton Oklahoma observes Mountain time though they are officially in the Central tim zone.

NM: Nara Visa New Mexico observes Central time though they are officially in the Mountain time zone.

TX: Guadalupe Mountains National Park and the surrounding area of the NW Corner of Culburson County observes Central time though all of the county is officially in the Mountain zone. Even the National Park observes Central time, an oddity itself in that federal facilities rarely follow local unnoficial exceptions. This exception is so firmly entrenched in the area that it is widely mistaken as official. The distance to which the observance of this exception extends south and east of Hwy 180 is arbitrary. That part of the county is sparsely populated and appears to have no services, so the point is somewhat moot.

AL: Phenix City Alabama (no, that's not a typo... though it may have started out that way - but maybe not) and the area witin a 10-15 mile radius on the AL side of the state border observes Eastern time, even though they are officially in the Central time zone.

AL: Valley/Lanett Alabama and the area witin a 10-15 mile radius on the AL side of the state border observes Eastern time, even though they are officially in the Central time zone.

AK: Hyder Alaska unofficially observes Pacific time, even though they are officially in the Alaska time zone. But the post office, being a federal facility, is on Alaska time.

AK: The Annette Island Indian Reservation near the southern tip of Alaska observes GMT-8, the same as Pacific Standard time, year round. It does not observe Daylight Saving time. So in the winter it matches British Columbia, and in the summer it matches Alaska.

SD: The city of Fort Pierre South Dakota (legally in the Mountain time zone) and a large radius on the west side of the Mountain/Central border observes Central time. Research determined that the distance this observance extends to the west is a matter of disagreement among the locals. After some effort to get a definitive answer I gave up and arbitrarily selected 20 miles, though I heard credible opinions that it stretched out as much as 50 miles. There are no services and very few residents in the western part of Stanley county, so the point is somewhat moot.

CA: Winterhaven California, in deference to its proximity to Yuma AZ, observes Mountain Standard Time year round. This means that (like AZ) Winterhaven does not observe Daylight Saving time. So this puts Winterhaven ahead of California by one hour (in sync with Arizona) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is locally considered to be the border of the Fort Yuma-Quechan Indian Reservation.

CA: Earp/Vidal California, in deference to its proximity to Parker AZ, observes Mountain Standard Time year round. This means that Earp and the surrounding area does not observe Daylight Saving time. So this puts Earp ahead of CA by one hour (in sync with AZ) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is estimated, but it is reported to extend to somewhere between Vidal and Vidal Junction.

Saskatchewan: Two things are odd about the time in the province of Saskatchewan. Firstly, it observes Central Time instead of the Mountain Time Zone in which most of it geographically resides. Secondly, it does not observe Daylight Saving time, remaining on Central Standard time (GMT-6) year round. There are a couple of exceptions in border areas - see below.

Saskatchewan: The western city of Lloydminster area, which straddles the provincial border with Alberta, officially observes Mountain Time including Daylight Saving time

Saskatchewan: The eastern towns of Denare Beach and Creighton which are near the provincial border with Manitoba, observe Daylight Saving time in order to remain in sync with the Manitoba town of Flin Flan.

British Columbia: The Peace River Regional District (a large chunk of east-central BC) observes Mountain Standard time year round, and does not observe Daylight Saving time. This includes Dawson Creek, Fort St. John and the surrounding area. So in Spring/Summer they are in sync with the rest of BC (which observes Pacific Daylight time). But in the winter they instead sync up with their neighbors to the east in Alberta. (NOTE: In November 2015, the "Northern Rockies Regional Municipality", which sits just north occupying the northeast corner of BC, will change its time observance to match the Peace River area. Interestingly, this observance may itself be an error: "In a 1974 referendum vote, Peace River Regional District communities voted to change their time zone to Mountain Standard Time all year round. The referendum had four options on it, including Mountain Standard Time and Mountain Standard with Daylight Savings Time. According to local historian Larry Evans, most residents wanted the second option, but accidentally voted for Mountain Standard Time without Daylight Savings Time."

Quebec: The eastern end of Anticosti Island, and that portion of mainland Quebec laying north of the island and west of the Natashquan river, now officially observe Eastern time.

Ontario: Southern Ontario, west of Thunder Bay, an area including Upsala, Shebandowan and Atikokan locally observes Eastern time even though they lie in the Central time zone. Also, the Atikokan portion of this area, including Quetico Provincial Park, does not observe Daylight Saving time, though in some descriptions they are said to observe Central Daylight time year round - which is the same thing in wall clock time.

Ontario: The towns of Pickle Lake and New Osnaburgh do not observe Daylight Saving time.

Ontario: The "Big Trout Lake" area observes Central time. The border is drawn by estimate.

Nunavut: Though the community of Arctic Bay on the western edge of Baffin Island is technically in the Central Time zone, it observes Eastern time to keep in sync with the bulk of the island.

Nayarit: This Mexican state is in the Mountain time zone, but in April 2010, Bahia de Banderas at its southern tip officially shifted into the Central time zone to sync up with Puerto Vallarta across the border in the state of Jalisco.

Other oddities:

Canada, Newfoundland:

  • Another Newfie related tidbit: Because the eastern bit of Quebec does not observe daylight saving time, during DST the 20 mile ferry ride from Newfoundland to Quebec involves changing your watch an hour and a half. Just half an hour in Standard time.
  • One last thing: Just off the tip of Newfoundland's Burin Peninsula sit the islands of St. Pierre and Miquelon. These are French holdings. Not French Canadian, French. They have their own time zone, "Pierre & Miquelon Time", which is one hour later than the Atlantic Time Zone, putting it half an hour later than Newfoundland.

    So if you are planning to take the ferry don't forget that the island ferry terminal in Saint-Pierre is half an hour later than the Newfoundland terminal in Fortune.

The Aleutian Islands of Tommorow (or yesterday?)

  • The westernmost few islands in the Aleutian chain actually push the Hawaiian/Aleutian time zone a few degrees west of the 180 degree line. Not to worry - the powers that be nudged the international date line out of the way so all of Alaska is on the same side of the date line, along with the other 49 states.

Daylight Saving Time (explained!)

Note: Frequently referred to as Daylight Savings Time, which is incorrect. It's "saving", not "savings".

In the movies, the major blockbuster action thriller "Daylight Saving" was based on the hidden drama behind Daylight Saving Time. Click here to see the amazing trailer.

US and Canada: DST starts 2AM the second Sunday in March, and ends at 2AM the first Sunday in November.

Our data presumes that by default most North American locations follow DST (not necessarily on the same schedule). Exeptions are discussed below:

  • Meanwhile, back in the desert: Even though Arizona does not observe Daylight Saving Time, the Navajo Indian Reservation (which takes up most of northeastern AZ) does observe DST. To add to the confusion, the Hopi Indian Reservation, which is wholly enclosed within the Navajo Reservation, does NOT observe DST. Confused? We're just getting started.
  • Consider also that the Navajos have an enclave containing the village of Jeddito, entirely within the Hopi reservation. And that the Hopi reservation has an exclave at Moenkopi, just south of Tuba City. Still not confused?
  • Some of the businesses in Tuba city (within the Navajo Reservation) reportedly do not observe Daylight Saving time, so as to avoid confusing the tourists. Good luck with that. At least that puts them in semi-sync with their Hopi neighbors across highway 160 in Moenkopi. Got it?
  • There is a small Navajo exclave south of the main reservation, just inside the AZ border with NM. Three miles of Hwy61 runs through it, but it looks as if there are no businesses, residences, or other significant through roads crossing this stretch, so to avoid adding to an already confused situation, I left that off the map.

Hawaii does not observe Daylight Saving time.

Indiana: As of 2005, the whole state observes Daylight Saving time. Prior to that only parts of the Hoosier state observed DST.

Newfoundland/Labrador: As of the Spring of 2011, Newfoundland officially shifted their Daylight Saving Time transition to 2AM. Prior to that Newfie DST started and ended at 12:01 AM, 119 minutes earlier than the rest of Canada and the US. So before 2011, when Newfies returned to Standard Time in the Fall, at one minute after midnight Sunday morning they not only changed time, they changed date - reverting back to 11:01PM Saturday. I can't imagine why they did that, but I am fairly certain the computer geeks were not consulted.

St. Pierre and Miquelon: These islands off the coast of Newfoundland are French, and thus part of the EU. They have their own time zone. However, they follow Canadian DST date and time observance, not EU (European Union) dates and times, which are different.

Mexico: Except for 10 border towns which officially follow the US DST schedule (Tijuana, Mexicali, Ciudad Juarez, Ojinaga, Ciudad Acuña, Piedras Negras, Anáhuac, Nuevo Laredo, Reynosa and Matamoros), Mexico starts DST at 2AM on the first Sunday in April (3 or 4 weeks before the US), returning to Standard time at 2AM on the last Sunday in October (one week before the US). This causes a temporary difference between US and Mexican time even in the same time zone. The state of Sonora does not observe DST at all, in sync with Arizona - its northern neighbor.

Mexico/Oaxaca: Most municipalities in the southern Mexican state of Oaxaca refuse to honor DST. This is an ongoing dispute with their federal government and may change. These Oaxacan DST exceptions are not documented and thus are NOT reflected in the data.

Some North American Amish communities opt not to observe DST, which they call "English time" or "Fast time", opting instead to follow "slow time" (Standard Time) year round. These Amish DST exceptions are not documented and thus are NOT reflected in the data.

Central American countries including Belize and Guatemala which are on Mexico's southern border, do not observe Daylight Saving time. Thus, in the Summer time (DST), there is a time transition between Mexico and it's southern neighbors - reflected in light blue on the map. The next time zone to the south is the Central/Eastern time zone border between Panama and Costa Rica. Because neither observes DST, the time transition at their border is year-round and remains drawn in magenta. So during DST, departing that that portion of Central America north of Panama you jump forward an hour no matter whether you are heading north into Mexico, or south into Panama.

Caribbean and Central American islands (we concern ourselves only with those in the Eastern and Atlantic time zones) have a mix of DST observance, and the situation sometimes changes with little notice. Cuba, the Bahamas and the Turks and Caicos Islands currently observe DST. As of this writing the Cayman Islands are studying a possible shift to observe DST.

Cuba has been changing their clocks on the same dates as the U.S., etc., since 2013, but their changes happen at midnight standard time -- midnight CUST(EST) & 1 AM CUDT(EDT).

Though Bermuda is not technically part of North America, and is well north of the Caribbean, it is worth noting that it also follows DST, on the US/Canada schedule.

Haiti has an erratic history of DST observance. They observed it 1983-1997 and 2005-2006. At the last moment they announced a return to DST observance (using the US/Canadian shedule) in 2012. During DST, this restores them to being the same local time as their neigbors, the Dominican Republic, with whom they share the island of La Hispaniola. Haiti is on Eastern time. The Dominican Republic is on Atlantic time and does not observe DST. So they will be in sync (GMT-4) in Spring/Summer, and Haiti will be an hour behind in Fall/Winter. As of 2014 Haiti still observes DST and apparently intends to for the near future. It may be best to check first if it matters to you.

European Union: Though outside our area of focus, it may be useful to keep in mind that the EU differs from North America by observing DST from the last Sunday in March to the last Sunday in October. All EU countries shift at the same moment (1AM GMT) no matter what time zone that country observes.

More Notes

The borders in were drawn primarily for road travelers. Little attempt is made for precision over roadless areas or over water. This is not focused to benefit offroad travlers, aviators or sailors. I did take care to keep the line on the correct side of any inhabited islands.

Wherever the real time zone border follows an irregular boundary such as a river or a ridge, I did not try to exactly mimic the boundary - which would have taken too many data points. Instead I generally tried to keep the line simple while not letting it touch or cross any roads except at the correct points where that road actually does cross or touch the real time zone boundary. So it may look a bit "low res" when you are zoomed way in, but there (hopefully) should be no instances where any part of a road is on the wrong side of a time zone border line.

For a description of just how difficult dealing with time zones can be, watch this youtube video. It will make you laugh, and leave you sympathetic to those who need to worry about such things.

Acknowledgements, Credits and Thanks

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