Rental car companies seem to want to know your entire life history when booking your reservation for a rental car.

But when they ask for your flight number, they really do have a good reason: so they can protect your reservation in case your flight is delayed.

These days, that’s a good precaution because flight delays are increasing.

The air traffic system in the United States relies on 26 hub airports that have become bottlenecks, driving the average flight delay from 41 minutes in 1990 to 57 minutes in 2009.

The Department of Transportation’s Bureau of Transportation Statistics treats any flight that departs from the gate within 15 minutes of its published departure time or arrives at the gate within 15 minutes of its arrival time as being “on-time.” Any flight that departs or arrives later than 15 minutes is treated as delayed.

Airlines are reluctant to announce a flight delay until they are 100% certain a delay will happen. That’s why it pays to check where your flight is coming from and call the airline to find out if it left on time.

In 2009, 23% of all flights arriving at Miami International Airport in Florida were late, according to Bureau of Transportation Statistics, with an average delay time of nearly 57 minutes.

American Airlines had slightly worse than average delay times, with 24.14% of its flights delayed when arriving in Miami, with an average delay time of nearly 61 minutes.

United Airlines did slightly better, with 19% of its flights delayed an average of just over 61 minutes.

Nearly 22% of Delta’s flights were delayed and an average delay time of 47 minutes.

Maybe having a nosy car rental company isn’t such a bad thing, after all.