National Work Zone Awareness Week (NWZAW): The Evolution and “Extreme Necessity” of Advance Warning Signs for Construction Zones

Advance warning signs have long been one of the defining features of road construction and maintenance areas across the United States. The Road Work Ahead sign, which serves as a crucial means of alerting drivers that they are approaching such an area, is one of the more familiar and readily identifiable temporary diamond-shaped fixtures regularly installed near those locations. The purpose and prominence of that particular sign, as a matter of fact, extends well beyond their actual presence in close proximity to work zones.

This symbolic significance was underscored in a United Press International (UPI) story in 1973 that discussed a wide-ranging “Drive Friendly” campaign begun in California to urge motorists to be extra cautious when traveling through work zones in that state. A major part of this campaign, according to UPI, were roadside billboards bearing the message: “The highway maintenance men ask you to drive friendly.” These billboards also featured a drawing of the Road Work Ahead sign.

The origins of that uniform advance warning sign and others used for work zones can be traced as far back as the 1920s. In 1922, the Mississippi Valley Association of State Highway Departments (MVASHD, now known as the Mid America Association of State Transportation Officials) appointed a committee to examine the viability of standardizing road signs. At its annual meeting in 1923, MVASHD approved the committee’s recommendations for a uniform system of signs.

One of the committee members was A. H. Hinkle, the superintendent of maintenance for the Indiana State Highway Commission (a predecessor of the present-day Indiana Department of Transportation), and his article about the findings of the group was published in 1924 in Good Roads: The Journal of Highway Engineering and Transportation. Hinkle noted MVASHD’s “recognizing the extreme necessity of standardizing [highway] signs,” and he also stressed the ever-growing demand for such consistency along the nation’s routes.

Hinkle wrote, “The standardization of danger, warning, and information signs on our highways is becoming more and more important each year due to the greater inter-county and inter-state traffic.” In specifically addressing warning signs, Hinkle emphasized the committee’s conclusion that they “should be uniform in all States.” He also reiterated the committee’s recommendation that state-by-state warning signs cautioning drivers to slow down should be diamond-shaped.

The evolution of that type of warning sign continued to evolve on a nationwide basis over the next several decades. The 1961 edition of Manual on Traffic Control Devices for Streets and Highways (MUTCD), for example, included a new section that addressed more specifically than before recommendations for warning signs used for work zones. This added emphasis was due in large part to the notable expansion of highway construction projects throughout the United States by that time and the consequent need to further improve safety in those settings. The guidelines set forth in the 1961 edition of MUTCD for construction zones included having those signs designed with black lettering on a yellow background.

The color for the background of construction zone warning signs was changed to orange in the 1971 edition of MUTCD. The use of orange in other regulatory signs and traffic control devices in and near work zones was also introduced in that edition. The 1978 version of MUTCD underscored the preference for that new color for road construction and maintenance operations by stating, “The high conspicuity of fluorescent orange colors provides an additional margin of safety by producing a high visual impact in hazardous areas.”  

With their longtime color and shape still in use today, the Road Work Ahead signs — and other warning signs likewise designed to temporarily help slow down traffic — have continued to play a lifesaving role for those individuals carrying out their jobs in work zones. This role was highlighted by Roxane Arnold in a 1979 Los Angeles Times article of hers that focused on California Department of Transportation (Caltrans) road crews.

“Usually, the first warning sign is posted about a mile [1.6 kilometers] before the work begins,” wrote Arnold in describing the start of the daily routine for those crews. “A Caltrans truck with warning lights and arrows blinking furiously pulls to the shoulder of the road. Doors on each side open quickly and workers fall out to pull the bright ‘Road Work Ahead’ sign from the truck bed. The workmen are cautious as they place the warning close to the lane of oncoming traffic.”

(The above photo features a Road Work Ahead sign that was installed for drivers approaching a work zone in the vicinity of U.S. Route 1 in Baltimore.)

Additional information on warning signs for work zones is available at

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