In October 1970, a road in California underwent an unlikely experiment: replacing most of the asphalt pavement with glass from discarded bottles. As we will see, the road worked, but the most interesting thing came later. In the decades that followed, other cities took that idea even further, from Baltimore’s glittering streets to New York’s traffic and the tons of recycled glass under today’s Australian highways.
A road made of bottles. It all began on October 26, 1970, when workers began paving a road in an industrial park in Fullerton, California, using a material that looked more like a recycling plant than a road. It was called glassfault, a mixture of conventional asphalt and crushed glass from discarded bottles.
The test covered a section about 183 meters long with a layer 7.6 cm thick. The idea responded to a growing problem: millions of glass containers end up in landfills, and researchers wanted to see if they could become raw material for road construction.
63% was glass. The recipe was extraordinarily ambitious: the mineral aggregate was composed of 63% crushed glass, 36% rock dust and 1% hydrated lime, to which asphalt binder was added. The bottles were crushed using a hammer mill and mixed with other ingredients before spreading the pavement.
Plus: the people responsible for the tests reserved a strip of road for conventional asphalt, so they could compare the behavior of both materials under the same traffic. Calculations at the time estimated that about three million bottles would be needed to pave a mile of lane with glass proportions.
And blocked the road. The first difficulties appeared during construction. Glass retains heat longer than conventional aggregate, complex compaction and some particles break under the weight of rollers. There were also concerns about reflections, dust and long-term resistance to pavement.
However, subsequent inspections showed that the material could withstand traffic and offer more than acceptable slip resistance. Of course, the experiment did not prove that glass is better than stone, but it did show something important: a part of the waste of cities can end up under the wheels of their cars.
The test was manifold. Because Fullerton was no isolated oddity. According to the United States Federal Highway Administration, approximately 33 experimental sections were constructed from recycled glass in the United States and Canada from the late 1960s to the early 1970s.
The researchers tested different ratios, particle sizes and compositions to determine how far the discovery could go. These tests confirmed its effectiveness, but also revealed that using large amounts of glass does not guarantee good results. In fact, the real advance would be to reduce its presence in the mix.
Baltimore wanted streets that were bright. In the mid-1970s and mid-1980s, Baltimore turned glassfault into a technological experiment. At least 17 of the city’s streets are paved with a combination of recycled glass to create a strange visual effect: small glints caused by the sun’s reflection on the pavement or street lights.
It is a way of recycling the waste which has given the roads a different look. Conversely, that feature also had a counterpart: too much reflection could cause visibility problems, especially on wet surfaces.
New York has turned it into an industry. The real leap in scale came in the following decades. In the mid-1980s, a glass processing facility on Long Island processed more than 12,600 metric tons and began preparing the waste for use as an alternative to traditional aggregates.
But it was New York that took the concept even further: Between 1990 and 1995, its Department of Transportation used about 225,000 metric tons of recycled glass in resurfacing work. What began in California as an experimental 600-foot road has become a full-scale urban application.
The big lesson: less glass works better. Decades of experimentation disproved parts of Fullerton’s original argument. The Federal Highway Administration has concluded that mixtures with large glass fragments and proportions greater than 15% are prone to spalling, adhesion problems with bitumen, and corrosion due to moisture.
The solution was to crush the glass until particles smaller than 4.75 millimeters were obtained and use it as a partial substitute for sand, usually in a ratio of 10% to 15% for surface layers. Processed well, the material can offer performance comparable to conventional asphalt. The secret was no longer to make a road with as many bottles as possible, but to find the right amount.
And Australia picked up the baton. Decades later, the concept found new impetus on the other side of the Pacific. In 2023, the Australian municipality of Port Stephens tested an asphalt mix that combined recycled glass, used tires and reclaimed asphalt. Two interventions in Glenelg Street and Ferrodale Road included the equivalent of 80,750 glass bottles and the material from more than 1,100 tyres.
According to the municipality’s calculations, the project avoids about 13.7 tons of CO₂ equivalent emissions compared to the use of virgin materials. Laboratory tests also show improved resistance to warping and cracking, although long-term performance needs to be further evaluated.
From testing millions of bottles. The Australian Paving the Way program, developed by municipalities in the Sydney area, provides one of the best examples of how far this idea has come. According to municipal documentation from November 2024, the initiative has allowed the equivalent of 10.8 million glass containers to be recycled annually to make asphalt, while the city of Sydney itself incorporates more than 500,000 containers per year into its pavements.
In its 2024-2025 environmental report, the city council also documented road renovation works with a mix of 20% reclaimed asphalt and 2.5% crushed glass. More than half a century after Fullerton, glass has gone from an experimental hero to a common material in certain paving projects.
Why didn’t we replace all the asphalt. Despite the results, glassfaults never massively displaced conventional pavements. The reason? The glass must be carefully collected, cleaned, crushed and classified to avoid excessively large fragments or contaminants that compromise the strength of the mixture. In addition, the material does not absorb bitumen like some natural aggregates and may cause adhesion problems if water penetrates.
Added to this limitation is an economic problem: obtaining sufficient quantities of processed glass, of constant quality and at a reasonable distance from asphalt plants. The Federal Highway Administration itself has identified a lack of regular supplies as one of the main obstacles to expanding its use.
What came after Fullerton. In 1970, California wanted to find out if a road could be built from broken bottles. The answer was yes, but the real story was written over the next 56 years. Baltimore has used glass to brighten its streets, New York has incorporated it by the tens of thousands of tons, and Australia has integrated it into projects that combine various wastes to reduce raw material consumption.
The original experiment with 63% glass aggregates taught something that seemed contradictory: for the concept to work better, much less glass had to be used. If you will, the revolution did not convert all roads to glass surfaces, but rather to ensure that millions of bottles stopped being littered and found a place under the asphalt.
Picture | Orange County Archives, David Herrera
In Xataka | The US built its roads so straight that it was not for cold war landings. But there is one country that has made it a reality
In Xataka | Texas has a 26-lane highway 37 kilometers long: still it can’t eliminate traffic jams
