The season will start in St. Petersburg on March 13 and finish at Sonoma on September 18, making it five weeks longer than the maligned 2015 schedule, which concluded on August 30.

Road America’s return was announced in August, while the April 2 Phoenix race will be IndyCar’s first there since 2005.

The Boston event on September 4 will take place on a new, 2.25-mile street circuit on the South Boston waterfront.

“Road America and Phoenix are great venues and two of the best choices that we could have to add to the schedule,” 2015 IndyCar champion Scott Dixon said.

“I’m looking forward to both race events.

“Road America is an old-school track that I always look forward to.

“Phoenix was a fun track for me in the past. I tested there [earlier in 2015] and the changes that they’ve made has maybe opened up quite a few different grooves.

“The racing will be very exciting; we’ll put on a great show.”

The 100th Indianapolis 500 will be run on May 29.

New Orleans Motorsport Park leaves the calendar after just one troubled event, while the Fontana and Milwaukee ovals are the other dropped venues.

2016 INDYCAR CALENDAR

March 13 St. Petersburg
April 2 Phoenix
April 17 Long Beach
April 24 Barber Motorsports Park
May 14 Indianapolis road course
May 29 Indianapolis 500
June 4 Detroit
June 5 Detroit
June 11 Texas
June 26 Road America
July 10 Iowa
July 17 Toronto
July 31 Mid-Ohio
August 21 Pocono
September 4 Boston
September 18 Sonoma