American Eagle Airlines, Comair (Delta Connection) and Continental Express were ranked as the three largest regional carriers, in terms of passenger enplanements, during 1999. The top 50 regional airlines, as ranked by enplanements, transported 99.6 percent of the industry's passengers and flew 99.9 percent of the industry's revenue passenger miles.
Safety.
Safety as a whole in the airline industry is leaps and bounds ahead of other forms of transportation. David Vinson who spoke as an FAA administrator said it best in August of 1996 when he commented, "You"d have to fly one flight a day for 27,000 years to be assured of being a fatal aviation statistic in the United States" (Human Factors pg. 32). However, airline statistics are difficult to breakdown. Dozens of different aircraft are grouped together with dozens of carriers who are then grouped with dozens of airports who are then grouped with dozens of countries. Other problems arise when you consider accident rates. If you rate accidents by total miles flown, long international flights receive an unfair advantage as they carry more miles per one takeoff and landing. Since most accidents occur during the critical phases of flight of takeoff, approach and landing, it's easy to see how rating accident rates per mile skews the data toward longer flights. Regional carriers suffer the greatest from the rating of accidents per mile as they by definition have shorter routes. If instead of rating accidents per mile, you rated them per cycle (One cycle being 1 takeoff and 1 landing) regional airlines have a comparable safety record to that of the major airlines (Human factors pg 37 table 2.2). .
Large airplanes are also touted as being more reliable because they have multiple redundant systems that back up major equipment failures. That their engines are more reliable and that larger airlines have stricter regulatory requirements that lead to a better safety standard.