An Influential 1920s Road Test is Conducted in Illinois

Between 1920 and 1923, the Illinois Division of Highways (IDH) –now part of the Illinois Department of Transportation — oversaw a series of tests to help determine the best type of pavement to use on that state’s roads. IDH launched these tests at a time when it was preparing for major construction projects to accommodate increasingly heavy motor vehicle traffic throughout the Prairie State.

The tests specifically took place on a two-mile (3.2-kilometer) stretch of road that had been built by IDH on state property near the community of Bates in central Illinois. The experiments conducted on that segment became collectively known as the Bates Road Test. This experimental road encompassed a total of 63 sections of pavement that were each 18 feet (5.5 meters) in width and anywhere from 100 to 250 feet (30.5 to 76.2 meters) in length. Twenty-four of these sections were built of concrete, 22 consisted of bricks, and 17 were made of asphalt.

Contractors’ and Engineers’ Monthly magazine noted, “In each type of pavement, the sections varied from those so thin that they were sure to break under the lighter test loads, to sections which were considered strong enough to successfully support the heaviest load permitted by the state traffic laws.”  (The above photo depicts one of those 63 sections of the Bates Experimental Road.) During the tests, a fleet of U.S. Army trucks made thousands of round trips on the road. These vehicles carried loads of up to 10 tons (9.1 metric tons) for their runs.

The Bates Road Test was widely hailed as a big success. The Associated Press reported in 1926 that this “experimental road attracted international attention when information on hard road building was scarce.”

The results of the Bates Road Test indicated that, in terms of durability, concrete was the best material for building highways at that time. Clifford Older, IDH’s chief engineer, focused on how the test runs showed the need for increased strength at the edges of a road. Older explained “Rigid pavements having a uniform thickness or edges thinner than the center are greatly unbalanced in strength and will fail along the edges long before the wheel loads are reached which will cause the destruction of other portions of the slab”

H.F. Clemmer, IDH’s engineer of materials, likewise highlighted the benefits of the Bates Road Test. He noted in the August 1923 issue of Municipal and County Engineering magazine, “Three years of investigation on the Bates Experimental Road has provided an immense volume of data on the actions and characteristics of the soil making of the subgrade of that road.”

Over the next several decades, the legacy of this road test eventually extended well beyond the borders of Illinois. As one of the best-documented initiatives of its kind during that era, the Bates Road Test helped set the stage for larger-scale efforts that were also undertaken to assess the most optimal materials and designs for the development of long-lasting roads. These efforts included several loading tests on concrete pavement that were conducted by the U.S. Bureau of Public Roads during the 1930s.

In 1950-51, a research project was carried out in Maryland to gauge the service life of highway pavements and the impact of wheel loads. This project, which was called Road Test One-MD, was administered by the Highway Research Board (the present-day Transportation Research Board) and financed by the District of Columbia and 11 states. The Maryland study used an existing road near the town of La Plata to test the impact of round-the-clock truck traffic on concrete pavements.

In 1953-54, the Western Association of State Highway Officials (WASHO) sponsored a road test in Idaho. The WASHO Road Test focused on the impact of heavy truck traffic on flexible (asphalt) pavements. This road test – likewise administered by the Highway Research Board – was financed by a total of 11 state highway departments.

An even more comprehensive experimental effort took place with the AASHO Road Test between 1958 and 1960 in Illinois. This series of tests was sponsored by AASHO and supervised by the Highway Research Board. The AASHO Road Test was carried out carried out along a seven-mile (11.3-kilometer) track of two-lane highway between the cities of Ottawa and LaSalle, an area that is approximately 125 miles (201.2 kilometers) north of where the Bates Road Test had occurred.

For more information on the Bates Road Test, please check out https://sangamoncountyhistory.org/wp/?p=2601