Board Thread:Questions and Answers/@comment-71.199.50.237-20151015223430/@comment-26518423-20151016020337

That is an interesting comparison and the reason for the extra earn power of the mail car is because it is carrying a large volume of mail in comparison... 1350 letters vs 125 passengers (100 passengers plus 25% bonus). Keep an eye on special offers. Soon you'll be offered cars that carry 400 to 650 passengers, with large bonuses (450%), and few mail cars can come close.

I concentrate on moving as close to 100% of my passengers as possible. Mail will continue to collect, but max passengers are limited by your flags and buildings... so get them while you can. With the larger cars, you can earn 250,000 coins per car, on a 24 hour run, with only 3 or 4 flags. With a single Refro engine (65 cars) that's 15 to 16M coins per 24 hour run, 40,500 passengers.