Test sessions for NASCAR teams before the DeVilbiss 400 race in two weeks have been canceled so protective fencing around the Michigan Speedway can be raised.

The move is an attempt to prevent another tragedy such as the one at the U.S. 500 on July 26 that killed three fans."Our staff will work around the clock if necessary to complete the job," Gene Haskett, president of Michigan Speedway, said Monday in announcing the higher fencing.

The improvements will begin in turn three, near where Adrian Fernandez's Indy-car slammed into the wall, launching a wheel into the stands. The improvements will continue through the front stretch and finish between turns one and two.

The top portion of the fence, which angles over the track, will be lengthened by 4 feet. The extension will add about 21/2 feet to the fence's height, for a total of 17 feet.

Haskett said Michigan Speedway has hired a consulting firm from Columbus, Ohio, to study the matter and make recommendations. He said he was unsure when it would be finished or how much the work on the track will cost.

"Our total focus is on completing the project," he said. "We have not looked at the cost yet."

The accident was the worst ever at the speedway. Killed were Kenneth Fox, 38, of Lansing, and Michael T. Tautkus, 49, and Sheryl A. Laster, 40, both of Milan. Six other spectators were injured.