Herdic

A herdic is a type of horse-drawn carriage, used as an omnibus, invented by Peter Herdic of Williamsport, Lycoming County, Pennsylvania in 1881.
A predecessor of the taxicab, the herdic was a small two-wheeled carriage that had side seats and an entrance at the back. Later versions had four wheels and varied in size from a small coach to a full size omnibus. The first four-wheel herdic cabs carried up to eight passengers. The major improvements over previous types of carriage were in the springs, the way the body was mounted on the springs, and the manner in which the axles, springs, body and shaft were connected. Herdics were designed as passenger vehicles, and, in particular, for use in public transportation. Their low entry made it easy for passengers to enter and exit the cars. This was especially advantageous for the women of the time, who wore full length dresses. 
The earliest herdics were painted bright yellow in order to be easily identified and quickly acquired the nickname "canary". This convention is presumably what led to many taxi cabs being painted yellow. Each cab was small enough to move freely through the city streets of Williamsport and leave its passengers at the curb instead of the middle of the street as other modes of public transportation were forced to do. 
Peter Herdic had moderate success with his cab and it was soon adopted in the cities of Boston, Philadelphia, New York, Washington, D.C., and numerous other cities. The herdic cab was in service in Washington as late as 1918.