After being adopted in 2008 and reviewed in 2013, Rule R307-123 was amended in December 2013. The amendments added language throughout the rule, allowing for intermediate and out-of-useful-life vehicles to be converted to run on alternate fuels, such as natural gas. Demonstration of eligibility requirements for vehicles converted to electricity were added to the rule. Furthermore, criteria was added for demonstration of eligibility for retrofitted vehicles in order to verify that the condition of the vehicle prior to the installation of the retrofit was compliant with the retrofit's certification criteria.