Auto Club Speedway had been dropped as a race venue for the 2016 Verizon IndyCar Series, after falling attendance and problems agreeing a suitable date on the calendar for the race in Fontana, California.

"There was a tremendous amount of effort put forth to keep Auto Club Speedway on the calendar," said Mark Miles, CEO of IndyCar's parent company Hulman & Co. "In the end, we could not identify a compromise for 2016 that was amicable for both parties.

"We mutually agreed that our inability to identify a date for next year doesn't preclude us revisiting these conversations in the future," Miles added.

In a press release, IndyCar officials said that they had explored several options to retain the event as part of its 2016 calendar, including plans to race later in the season to comply with the track's request to host the season finale but had been unable to fund a date and time both parties could agree on.

This year's event at the two-mile oval was a success in racing terms with some of the most exciting on-track action seen in the series in recent years. However the 'pack racing' style was also criticised by a number of leading drivers who felt that it was too dangerous and risked a serious accident.

As a result of some of the comments, IndyCar subsequently brought in new rules governing what teams and drivers could say about the series so that there wouldn't be damage to the IndyCar brand.

The race was successful in terms of television ratings, but had very poor attendance at the track itself which meant many felt that the race would simply not be economically viable in its current form.

Spectator numbers took a hit after Fontana lost the prestigious late-August season finale spot it had held for the previous two years. By making it a daytime race in June, the California temperatures also became a significant factor in attracting fans to the track.

It's believed that IndyCar is currently in late stage negotiations to replace Fontana with an event at Phoenix International Raceway, which is also owned by International Speedway Corporations.

It's been reported that Phoenix would be an early April race, slotting into the schedule before the race at Long Beach, and that it would be held under floodlights at the one-mile oval in Arizona.

The series recently confirmed that it would be returning to Road America next June for the first time since 2007, and would also be adding an inaugural race on the streets of Boston on Labor Day in September.