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America's Various Flirtations with the Metric System

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The United States and the metric system are like oil and water; they don't mix.  But that hasn't stopped us from trying.

Beginning in the 1970s and continuing into the 1990s, the United States would occasionally attempt to sign highways in metric units at different times.

Chapter 1: The 1970s

America's first modern foray into metric signs quietly occurred in 1971 in Huntsville, Alabama.  268 metric speed limit signs were placed throughout the city, courtesy of the metrication committee at Marshall Space Flight Center. (1)

Between 1971 and the passage of the Metric Conversion Act of 1975, a few states took the lead in marking highways in metric.  In 1973, Ohio became the first state to place metric signs along Interstate highways.  Starting with four signs in February, Ohio had at least 60 metric signs up along Interstate highways by the end of the year, including a 30-mile stretch of Interstate 75 between Dayton and Cincinnati. (2)  

In 1973, Ohio was the first state to place metric distance signs on an Interstate highway.  A section of Interstate 75 between Cincinnati and Dayton would have dual-distance (English and Metric) guide signs. (2)

The passage of the Metric Conversion Act of 1975 laid the groundwork for the voluntary conversion to the metric system within the United States.  On the highways of America, some states were beginning to warm up to it.

By the time the Metric Conversion Act passed, 13 states had begun posting metric highway signs. (Alabama, Arizona, California, Florida, Maryland, Michigan, Minnesota, New York, Ohio, Pennsylvania, Virginia, Vermont, and Washington.) (3)  Meanwhile, signs within the National Park System - like the Blue Ridge Parkway - were beginning to include metric distances.

This metric sign on the southbound Durham Parkway was installed along with a companion sign near Cary late in 1975.  The pair was North Carolina's initial metric distance sign.  While the other sign was removed, this sign stood tall for nearly 40 years. (Adam Prince - July 2010).

North Carolina posted its first metric sign in late 1975.  Signs along Interstate 40 and the Durham Freeway were posted with metric distances to Research Triangle Park and Raleigh or Durham.  Employees at RTP were to be surveyed on their initial reaction to the signs. (4)

Charlotte was also the site of a test case for the upcoming metric conversion.  At the intersection of East Independence Boulevard and Sharon Amity Road, four 70 kph metric speed limit signs were placed above existing 45 mph signs.  The signs were installed as part of a test by the Federal Highway Administration to see which design was most readable. (5)

Crews install a 70 kilometer speed limit sign on East Independence Boulevard in Charlotte, North Carolina (5)

Metric conversion would soon hit the first of the many roadblocks that would stall and eventually end any change.  After the Federal Highway Administration (FHWA) announced in April 1977 that it would convert all speed limit signs to metric by September 30, 1978, a debate on whether 55 miles per hour roads should convert to 88 or 90 kph added confusion to the switchover. (6)  The National Maximum Speed Limit was set at 55 mph in the 1974 Emergency Highway Conservation Act.  90 kph would be over that national limit by about 1.5 miles per hour.  An increase to 90 kph would require a change to the NMSL set in 1974.

Yet, before that change could be debated and signed into law, the push for signing highways in metric collapsed.  In June 1977, just two months after announcing moving forward with metric signs, FHWA director William M. Cox scrapped the plan for metric conversion on US highways. "There was simply too much opposition to the proposal from the general public," Cox said, "More than 5,000 comments were received, and about 98 percent of them were negative." (7)

States were allowed to keep dual Metric/English signs up - most took them down.

Chapter 2: Interstate 19

Metric wasn't done yet. While highways were not being signed in metric, various everyday items, such as food packaging, medicine, and of course, your 2-liter soda, were.  

In Arizona, metric highway signage was about to get a new life.  Interstate 19, a 63-mile corridor from Tucson to the Mexican border at Nogales, was nearing completion.  In late August 1977, the Arizona State Transportation Board announced that the completed Interstate 19 would be signed in metric as part of a pilot study to identify issues with a possible conversion to the metric system. (8)  The highway's short length, the need to still erect new signage around Tubec, and Mexico's use of the metric system were key factors in the decision. (8)

Metric distanced overheads on Interstate 19 South near Nogales, Arizona. (Dan Murphy, 2020)

The metric signs were scheduled to appear in 1978.  However, the new Interstate around Tubec did not open until the spring of 1979, and the metric signs on I-19 first appeared in May.  Metric distances appeared on all guide signs, as well as height clearances.  Initially, speed limits were to be signed in both English and Metric; however, "legal complications" resulted in speed limits posted only in English units. (9)

Although in recent years, pushes to revert Interstate 19 to English measurements have arisen, most of Interstate 19 remains signed in metric. 

Chapter 3: Florida Speed Limits

Florida decided to dip their toe into the metric pool in the early 1980s.  Newly installed speed limit signs within the state would include the English unit speed and its metric equivalent.  The kilometers per hour sign was placed below the miles per hour speed limit sign. 

Florida attempted to post metric speed limits during the mid-1980s.  By 1987, those efforts ended, though you could find leftovers well into the 1990s. (Josh Lintz - May 1992)

The metric speed signage appeared due to a 1983 Florida law requiring speed limits to be signed in both English and Metric units.  The bill's goal was to assist the growing number of international tourists visiting the state.  Metric speed signs were placed only when an existing sign needed replacement or in new signage projects. (10)

Florida's foray into metric signage didn't last long.  By 1987, when the NMSL increased to 65 mph (or 110 kph), the updated signs to reflect the new, faster speed limits did not include its metric partner.  Florida's flirtation with the metric system was over. (11)

Chapter 4: The 1990s - One Last Push

In the early to mid-1990s, there was another push to bring metric signage to the United States.  Beginning in 1988, a trade bill, a series of transportation bills, and a Presidential executive order created one final push to sign in metric.

With these directives, the FHWA required states to have metric signage in place by September 30, 1996.  Many states protested.  Some states, like Virginia, attempted to pass laws outlawing the metric system on their highways. (12)

Alabama posted kilometer markers
 in 1995, only for them to be
removed by 1998. (13)
Despite many states' opposition, new Metric distance signs, including dual speed limits, appeared sporadically throughout the United States.  

Alabama was a leader in this final attempt to convert to metric.  By the end of 1995, 36,724 kilometer distance posts were placed on highways throughout the state, and new kilometers per hour speed limit signs were installed. (13) The catch - a sticker with speeds in mph was placed over the kilometer speed, ready to be removed when a full conversion took place. (14)

Yet, by late 1997, they began to disappear.  After Congress passed legislation halting any requirement to convert to metric, public outcry in Alabama led the state's Department of Transportation to remove the kilometer markers by early 1998. (13)

Chapter 5: Leftovers

Drive anywhere in America today, and you are more than likely NOT to find a metric sign.  However, if you look hard enough, you'll find one.  Leftovers from the 80s and 90s are still common, yet the early 1970s attempts are more than likely long gone.  You can find most metric signs near the borders with Mexico or Canada.  Yet, I have found a leftover in Tennessee and Florida since 2021.

Metric distance sign to Knoxville, TN on Interstate 40 West.  (Adam Prince - November 2021)

Will there be another metrication push in the United States? Time will only tell.  Maybe before this website turns 50 years old.

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