The answer to the crossword puzzle for the term 'WHAT'S ON THE FAST TRACK?' is ACELA, which stands for the Acela Express, a high-speed train service operated by Amtrak along the Northeast Corridor in the Northeastern United States. The Acela Express is the only high-speed rail service in the United States and is capable of reaching speeds of up to 150 mph (240 km/h). It is the fastest train service in the United States and is on the fast track to becoming the preferred mode of transportation for many travelers.