INDIANAPOLIS — A possible unification of America's two open-wheel series is still on track, with both sides saying progress is being made.

David Higdon, Champ Car World Series spokesman, said discussions are "heating up," but no announcement was expected Tuesday. ' Both sides have struggled for fans, sponsors and TV ratings since the IRL, founded by Indianapolis Motor Speedway president Tony George, began competition in 1995, competing against the established CART series.

There have been numerous attempts over the years to get the two sides back together, several of them launched by longtime racing star Mario Andretti and Champ Car car owner Paul Newman.

Most of the previous negotiations broke down over the issue of who would control the merged series.