 Travel costs are slightly lower than a year ago, and that's helping traveler numbers reach historic levels. TSA projected Sunday to be the busiest day on record for air travel, and it was. More than 3 million passengers moved through checkpoints. The 3 million mark was a matter of time. This year has seen 8 of the 10 busiest days in history. The surge in passengers has been a good thing for airlines. Analysts expect Delta's second quarter earnings to be almost a billion dollars higher than last year's when they're announced this week.