Phases in the history of the US route system

Most US routes were commissioned in late 1926, but some were not created until later.  And while some highways have existed continuously ever since 1926, others have come and gone in just a few short years.  For quite some time I wondered how it would look to graph all of the US highways on a timeline, and when I finally had an opportunity to create one in 2019, it was interesting to see some of the patterns that showed up in the data.  In 2025 I published a book about the first century of the US route system, and I used the information below as a framework for organizing the book chronologically.  So if you like what you read on this page, you can find much more detail in the book. 

Methodology

The colors and symbolization used on the timeline are as follows:

• Each cell represents one year, starting on the left with 1926, and moving forward in time to the right.

• White (or no color): the years before a particular US route existed. 

• Bright green: the year a US route was commissioned. 

• Pale green: the subsequent years during which the route existed. 

• Bright yellow: the year a route was decommissioned (if the route became part of a different US highway).

• Bright red: the year a route was decommissioned (for any other reason). 

• Light red: the years after a route was decommissioned. 

That is only a low-resolution overview of the timeline, yet despite the high level of granularity, we can still recognize some patterns:

• Lots of bright green years in the far left column.  That is because the majority of US routes were commissioned the same year: 1926.

• White horizontal lines along the left edge indicate routes that were not commissioned until sometime after 1926.

• Light red horizontal lines along the right edge represent all of the routes that have been decommissioned.  It is clear from this chart that very few 1- and 2-digit US routes have been canceled (upper 1/3rd), whereas a far greater percentage of 3-digit routes have been decommissioned (lower 2/3rds).

​Based on the more detailed data in that chart, the timeline was divided into four vertical columns, representing four distinct phases in the history of the US route system:

• The leftmost column represents the years 1926-1939.  Notice the sheer amount of changes, both additive (green) and subtractive (red and yellow).  I refer to this time period as The Turbulent Years.

• Moving one column to the right, which represents the years 1940-1960, there was a marked decline in amount of changes, and almost all activity was additive (green), with virtually no subtractive changes (red and yellow).  I refer to this period as The Golden Age.

• During the timeframe represented by the third column (1961-1992), there was a notable increase in the amount of subtractive changes, and those were not offset by very many additive changes.  I refer to this period as The Years of Decline.

• The rightmost column shows the years 1993-present.  Notice that there has been very little activity of either type.  I refer to this current timeframe as The Marginal Years.

The Turbulent Years (1926-1939)

Although the inaugural map showing approved US routes was released in November 1926, that list was by no means "final".  Rather, within literally the first weeks and months after that route log was published, various state highway departments were already requesting changes.  And changes continued taking place at a rapid rate over the next 12 years, right up until the U.S. became involved in World War II.

The Turbulent Years were characterized by the following:

• Several new two-digit US route designations.  Not all two-digit numbers were assigned to routes in 1926; 18 numbers were left available for future additions to the system.  Five of those 18 have never been used (37, 39, 47, 86, 88).  But out of the remaining 13 numbers, 11 were assigned during the Turbulent Years (33, 35, 43, 44, 46, 58, 59, 62, 79, 82, 98).  Only two other 2-digit numbers would be assigned in later years (56 and 57).

• Several new three-digit US route designations.  60 additional three-digit branch routes were assigned during the 12-year period following 1926.

• Many US route extensions.

• Decommissionings of various US route designations.  In 1937 AASHO released a document which included the statement: "US routes, less than 300 miles in length, heretofore established and located wholly in one state, shall be eliminated either by consolidation with other US routes or by reverting to state routes..." [reference]  Several routes were deleted during the Turbulent Years, many in response to that document.  42 designations were retired because their routes were appended to other, longer US highways.  And ten additional routes were eliminated and replaced by state route designations.  Of those ten, nine were short intra-state routes.

• Some US route truncations, but again, the majority of these shortened segments were simply transferred to other US routes.

Scheduled airline service would not begin until the late 1950s, and the cost of airfare remained out of reach for most people through the 1960s or '70s.  However, automobile travel had started to become more affordable decades earlier, especially after WWII.  Bridging the Turbulent Years and the Golden Age, there was a period (from roughly the 1930s through the '50s) during which the US route shield was a symbol of status for people who had the means and enough leisure time to drive their car across the country.  It was quite common for vacationers to document their journey by pulling over and posing for photographs along with a US route signpost.  Several examples of this can be viewed in the photo carousels on the home page.

The Golden Age (1940-1960)

Since Pearl Harbor was attacked in Dec. 1941, one could easily conclude that the reason why US highway-related activity dropped off sharply around that time was because so much attention had been diverted to the war effort.  Undoubtedly that was a factor, but if WWII were the only reason for the dropoff, then one would expect activity to increase again after the war ended in 1945.  Yet that did not happen, so there must have been additional influences.  I believe another contributing factor was the aforementioned document that AASHO released in 1937.  With respect to US routes, the state highway departments were now operating under new lines of thought, such as "the U.S. numbering system needs perfecting rather than expansion", and "additional routes for U.S. numbering will be greatly limited" [reference].  These new guidelines ushered in what I consider to be the "Golden Age" of the US highway system.  During these two decades, the US routes were still the nation's elite, primary highways, carrying the bulk of interstate traffic, and they did not yet face competition from the modern Interstate Highway System.  The Golden Age was characterized by the following:

• ​A decline in the amount of new US routes.  Only 16 new routes were commissioned during the Golden Age (compared to more than 70 during the preceding Turbulent Years).

• A decline in the amount of changes to existing US routes.  But the changes that did take place consisted almost entirely of extensions (rather than truncations).

• A decline in the amount of US route eliminations.  During the Golden Age, only five routes were decommissioned (compared to 52 during the Turbulent Years).  In all five of those cases, their mileages were simply transferred to other US routes.

The Years of Decline (1961-1992)

In 1956 the Federal Aid Highway Act was passed, and this paved the way for construction to begin on the nation's Interstate Highway System.  In most cases, the Interstates were built along essentially the same corridors as the most heavily-traveled US routes.  In fact, some of the limited-access roads that eventually became segments in the Interstate system were constructed years earlier as improvements to existing US highways.  But when an Interstate was completed and opened to traffic, any parallel US routes became redundant, and in some cases, irrelevant.  The Years of Decline were characterized by the following:

• ​​General loss of favor.  Three decades earlier, during the Turbulent Years, proposed US highway alignments were challenged by people whose cities would not be located on the route in question, and defended by others who did not want the route to be moved away from their area [reference].  During the Golden Age, officials in towns that had been left out of the US highway system strove to have highways through their area recognized as US routes.  But during the Years of Decline a marked change in mindset began to settle in.  The bulk of interstate travel was now handled by the Interstate highways, and the old US highways began to seem like nothing more than state routes, except they were signposted with a different shield.  In fact, some state departments of transportation seemed eager to rid themselves of US routes wherever possible.

• Massive reduction of US highway mileage in California, and subsequent collateral damage.  Starting in the mid-1960s, California deleted or severely truncated almost every US route in their state, for the reasons listed above (most of these were either intra-state routes, or else they paralleled new Interstates).  Because of its geographic location (with no other states to its west or south), California had more freedom to delete these designations than an interior state would have.  But suddenly California was devoid of several long, coast-to-coast, or border-to-border US routes, including 40, 60, 66, 70, 80, 91, and 99.  And this had a ripple effect, opening the door for neighboring states to do the same: for example, Arizona soon deleted or truncated its portions of US 60, 66, 70, and 80.  Route 66 was redundant with various Interstates all the way to its eastern terminus in Chicago, and by 1985 the entire US 66 designation had been decommissioned.

• ​Significant reduction in US highway mileage due to eliminations of intra-state routes.  In the minutes of their June 1970 meeting, AASHO listed 20 single-state US routes (remarkably failing to mention an additional 17 that existed at the time).  Within the next decade, eight of the routes on that list had been decommissioned.  Altogether, about 20 intra-state US routes were decommissioned during the Years of Decline.

• Deletion of several US route concurrencies.  Many of the truncations that took place during the Years of Decline were due to the elimination of what were considered unnecessary overlaps of two or more US route designations.

• Extension of some US routes.  Despite losses elsewhere, some US highways that were not impacted by the Interstates continued to expand, although in general the pace of growth was slower than during the preceding Golden Age.

The Marginal Years (1993-present)

Research and/or image credits: Jim Lindsay; Dale Sanderson; Dale Sauter