The Times They Are A-Changing -- Across the Interstate

When heading across the country, it can feel like time slows down or moves faster—and sometimes it does! For the people that are familiar with long interstate drives, you’ve probably felt the effects of time zones and daylight saving time firsthand. When the dashboard clock starts conflicting with your cellphone, it’s easy to feel a little confused or disoriented. It can be comforting to know that this is just America’s complicated relationship with time, and we at Interstate Signways understand it well. Having to arrange interstate signage deliveries across state lines means we have to know where the time zones are and how that changes during daylight savings time. For those that may not be as familiar, let’s break down how time zones work, why daylight savings time still exists, which states skip it altogether, and where the lines aren’t easily defined, so that everything stays on schedule!

Time Zones

The United States spans six primary time zones:

• Eastern Time (ET) – New York to Florida

• Central Time (CT) – Texas to Illinois

• Mountain Time (MT) – Colorado, New Mexico, Utah

• Pacific Time (PT) – California, Washington, Oregon

• Alaska Time (AKT)

• Hawaii–Aleutian Time (HAT)

  
  

If you’re driving cross-country, maybe on I-40 or I-80, you might experience three or more clock shifts. Some highways will even alert travelers of upcoming time changes with roadsigns.Time zones are determined by when the sun is highest overhead, at which point should be noon. However, with a country this wide, the sun (or noon) reaches its highest point at different locations along the way.

The full history of America’s time zones starts with different forms of time marking (local mean solar time, local solar time, apparent solar time, etc.) that grew increasingly more complicated and difficult as the railways and telecommunications evolved—but we’ll save that for another blog post.

States that Split

A handful of states may feature different time zones within their borders. For example, Oregon, Kansas, Florida, Nebraska, Idaho, North Dakota, South Dakota, and Tennessee all sit on time zone boundary lines. Some of these states, like Indiana, have even seen heated political debates about which time zone to follow or whether to observe Daylight Saving Time at all.

• Indiana – Most of the state is on Eastern Time, but the northwest corner and the southwest tip follow Central Time. Since 2006, the entire state observes daylight saving time.

• Kentucky – About 60% of the state is on Eastern Time, while western counties run on Central Time.

• Tennessee – Eastern Time in the east (Knoxville, Chattanooga), Central Time in the west (Nashville, Memphis).

• Florida – Most of the state uses Eastern Time, but the Panhandle (west of the Apalachicola River) observes Central Time.

• The Dakotas – Both North Dakota and South Dakota split between Central and Mountain Time.

  
  

Crossing through these states, you’ll often see clear signage alerting drivers that they’ve entered a new time zone. It’s one more reminder that when you’re on the road, how important it is to stay attentive to changes that can alter your entire trip.

Daylight Saving Time

Daylight saving time (DST) was first introduced in World War I as a way to conserve energy by pushing daylight into the evening hours. The idea came back during World War II, and in 1966, Congress standardized the practice with the Uniform Time Act. Daylight saving time now follows a streamlined process. The second Sunday in March the clock jumps forward one hour—marking the “start” of daylight saving time. The first Sunday in November is when DST ends, when the clock falls back one hour. This little mnemonic may help, “Spring forward, fall back.” For drivers, DST means more daylight during the evening commute and summer road trips—but it can also mean darker mornings, groggy starts, and maybe one confusing Sunday each March and November.

States that Skip DST

Only two states refuse to join the fray: Hawaii and Arizona (except for the Navajo Nation). Hawaii opted out in 1967, pointing out that near the equator, sunrise and sunset don’t change much year-round. Arizona followed in 1968. When temperatures rose above 100 degrees Fahrenheit in the summer, residents argued for cooler mornings versus hotter evenings. Several U.S. territories—like Puerto Rico, Guam, and the Virgin Islands—also skip DST entirely. For travelers, this means your watch may not match what you expected when you roll across a state or territorial line.

Interstate Time Change Confusion

If you’re driving on I-10 from Louisiana to California, you’ll shift from Central, to Mountain, and Pacific time zones. If it’s the summer and you cross through Arizona, daylight saving time won’t apply. Catching a hotel check-in at a specific time might need some double-checking.

If you’re traveling on I-40 from North Carolina to California, you’ll cross not only three time zones, but also multiple split-state borders and a mix of DST rules. Though your phone or GPS usually adjust automatically, dead zones or spotty service might leave you confused. Keep an eye out for signage that will notify you that you’ve lost or gained an hour.

Here are a few tips to stay on schedule:

• Check the route before you leave. If your road trip spans states, look up where time zones switch.

• Know the DST dates. A March or November road trip may include a surprise clock change.

• Use your phone as a guide. Most smartphones adjust automatically—but confirm when service is patchy.

• Rely on signage. When in doubt, those “Entering Mountain Time” or “Now Leaving Daylight Saving” signs are your best reference.

  
  

Time zones and daylight saving directly affect travel times, reservations, and how long you’ll have daylight on the road. With a little planning, travelers can avoid surprises and keep their trips running smoothly. Though we can’t change the clocks for you, Interstate Signways makes the signs that keep America’s highways clear and dependable.