They are just two changes, but their significance cannot be overstated.

INDYCAR on Tuesday released its 2019 schedule, with two important differences from the 2018 schedule: Circuit of the Americas will replace ISM Raceway in the early days of the season, and WeatherTech Raceway Laguna Seca will replace Sonoma Raceway as the season finale.

“We could not be more delighted that (COTA) is a new feature on the calendar, and we’re stoked about Laguna Seca,” said Mark Miles (at right in above photo), president and CEO of Hulman & Co., which owns INDYCAR and Indianapolis Motor Speedway. “It’s hard to improve on Sonoma as a destination event, but if it can be done, Laguna Seca helps us do that.”

Circuit of the Americas, which opened in 2011 and hosts Formula One’s U.S. Grand Prix, will hold an INDYCAR race for the first time when the series visits the 20-turn, 3.4-mile permanent road course in Austin, Texas, on March 24. The reaction to the addition is being felt both by the series and the circuit.

“The response has been overwhelming,” said Bobby Epstein (at left in above photo), Circuit of the Americas founder and chairman. “It’s been building for years. It’s something they wanted to see from the very first year. It’s been nice that over time the drivers have heard from others who have participated and raced at the track and heard good things about it. They’ve been supportive in asking for this.”

Laguna Seca, the historic 11-turn, 2.238-mile permanent road course near Monterey, California, last hosted an Indy car race in 2004. It will return to the sport for a 23rd time when it ends the 2019 season on Sept. 22.

The additions were received positively after Tuesday’s announcement, which was made just two days after a successful return to Portland International Raceway.

“The addition of those two races, combined with the other strong races that are returning, is a huge benefit to our team and sponsors,” Rahal Letterman Lanigan Racing co-owner Bobby Rahal said in a statement. “After coming off our return to Portland (on Sunday) that was met by such an enthusiastic and strong crowd, INDYCAR is continuing the great buzz with this schedule announcement. We still have one more race in 2018, but I’m looking forward to 2019.”

COTA and Laguna Seca join a 17-race schedule that keeps much of its 2018 form intact. The 2019 season is scheduled to open for the ninth consecutive year with the Firestone Grand Prix of St. Petersburg on March 10. It’s followed two weeks later by the COTA debut. A 10th consecutive visit to Barber Motorsports Park in Birmingham, Alabama, is moved up two weeks from the 2018 schedule, to April 7.

The Long Beach Grand Prix, the second-longest running event on the INDYCAR schedule behind only the Indianapolis 500, returns for a 36th time on April 14. It’s followed by the INDYCAR Grand Prix on the Indianapolis Motor Speedway road course May 11, with the 103rd running of the Indy 500 on May 26.

Much of the heart of the summer stretch of the 2019 schedule remains intact. Detroit’s doubleheader street races on Belle Isle Park are set to resume their post-Indy 500 place on June 1-2, followed by Texas Motor Speedway on June 8 and Road America in Elkhart Lake, Wisconsin, on June 23.

“We’re proud of those long-term relationships,” Miles said. “Those events are getting better and growing. It isn’t going to be the same. I think it’s exciting that there are going to be a couple of new venues added for next year, but it’s familiar to our fans. I think people will be delighted by the changes that are a part of this and the things that are familiar.”

Iowa Speedway and the Honda Indy Toronto change places on the schedule, with Toronto set for July 14 and Iowa following with a night race July 20. That leads to a stretch run of Mid-Ohio Sports Car Course (July 28), Pocono Raceway (Aug. 18), Gateway Motorsports Park (Aug. 24) and Portland (Sept. 1), followed by the finale at Laguna Seca.

Circuit of the Americas made the most noise in the schedule news; drivers have been eager to race at the facility since its opening.

“It’s off the charts, whether it’s drivers who want to be there on that great stage in that great market on a world-class track or the team owners who want to bring their sponsors," Miles said. "Everybody is thrilled about it. Haven’t heard a peep of anything except enthusiastic support.”

The 2018 season concludes Sept. 16 with the INDYCAR Grand Prix of Sonoma at Sonoma Raceway. Scott Dixon leads Alexander Rossi by 29 points in the Verizon IndyCar Series standings heading into the double-points finale. The race airs live at 6:30 p.m. ET on NBCSN and the Advance Auto Parts INDYCAR Radio Network.