Teams can now choose how much fuel the cars carry on board at the start of the race, rather than be required to carry 18.5 gallons.
The series also announced that the car specifications will allow slightly less downforce at Iowa Speedway than 2012, while aerodynamic specs for the new event at Pocono are initially set at Indianapolis regulation.
All driver helmets will now have to meet FIA standards. The FIA 8860-2010 specification requires the helmet to pass single impact and shell hardness tests in addition to being certified to the Snell SA standard.
And in a minor but still welcome cosmetic move, the minimum size of the car numbers on the end-plates of the rear wing will be increased by one inch to eight inches after complaints about legibility.
In addition, Barfield also awarded the race director the power to park any car that interferes with the proper running of the qualification process. That means that if a driver does something to impede another, then the race director can delete that driver's two fastest laps, prevent the driver from progressing into the next elimination round or stop the driver from taking any further part in the current round.
"In 2012, the IZOD IndyCar Series saw an exciting season with an all-time high level of competition between our teams," Barfield summed up. "For 2013, we have adjusted processes and regulations throughout the rulebook to build on last year's successful introduction of a new car and engine package.
"In addition to enhancing the on-track competition and producing rules consistency, the 2013 rulebook is focused on changes that will make the sport easier to follow for our competitors and fans," he added.