Caltrans needed a way to build an off ramp embankment on a foundation of 30 feet of mud from San Francisco Bay, a weak layer of soil that cannot support heavy structures, without it settling or sinking unevenly over time - so they innovated - and used 6,627 tons of shredded tires (thank you George!)

Caltrans chose the tire aggregate: it weighed about 50 pounds per cubic foot, lighter than the roughly 60-pound alternative, and cheaper too. Tire-derived aggregate is made by shredding used tires into pieces a few inches across that can replace gravel, rock, or soil in construction projects.

the finished embankment is roughly 26 feet tall, 700 feet long, and 50 feet wide. 

Dr. DingXin Cheng of California State University, Chico, who documented the project for a CalRecycle usage guide, calls it the first embankment project where Caltrans used shredded tires this way, and notes that the same layered approach became standard practice on later projects of this kind.

The main goal behind using shredded tires was reducing stress on the fragile bay mud, and the numbers back that up. The built embankment put pressure of 2,250 pounds per square foot on the foundation ground. By comparison, a similar earth-filled embankment would have exerted 3,750 pounds per square foot

https://economictimes.indiatimes.com/news/international/us/in-2000-california-packed-6627-tons-of-shredded-tires-beneath-dixon-landing-road-the-lightweight-fill-saved-an-estimated-477000/articleshow/133702443.cms

So, since shredded used tires have proven to be really good for something, why are landfills still full of them, instead of them being shredded and preventing mosquitos from having a  place to create many more generations of blood thirsty skeeters?