Experience with road fills in Washington State constructed with thick layers of tire chips spontaneously burning has led to a decrease in tire chip use nationally. The field measurements and samples taken indicate that a pyrolitic reaction occurred at two roadfill sites in Washington State based on a comparison to know pyrolytic reactions in controlled settings. Pyrolysis in roadbeds containing tire chips is a new phenomena previously only found in open piles of processed tire chips. Because water and nutrients were introduced, iron oxidation, microbial digestion, and chemical oxidation are possible factors contributing to the pyrolytic reactions at the two Washington State sites. A new heat ignition theory from Japanese experiments suggests a theoretical answer to practical design depth limits in roadbeds and tire chip piles may be climate (air temperature) and depth dependent.