two-forty on a plank road

phrase2

1. •
   (slang, no longer used) A very fast speed.

   • The passion of young New York is for horses — fast horses — two-forty on a plank road. — 1852
2. •
   (slang, no longer used) The quality of being "fast", i.e. immoral in one's habits.

   • In Canada, where trotting is also a very favourite amusement, and whence came the famous trotting mare Flora Temple, a very “fast” young lady is generally spoken of as “two forty on a plank road.” — 1867