Originally Posted by UnofficialDLHelper

On the Flight Schedules page on delta.com click on the Historical Reliability Information link.

From there, you can click on Searchable Database.

You can search by many different criteria:

Summary Statistics - All and late flights (total number, average departure delay, average taxi-out and average scheduled departure) and late flights (total and percent of diverted and cancelled flights).

Detailed Statistics - Departure and arrival statistics (scheduled departure time, actual departure time, scheduled elapse time, departure delay, wheels-off time and taxi-out time) by airport and airline; airborne time, cancellation and diversion by airport and airline.

The most recent data is FEB2008; searching DL4511 doesn't show CLE-ATL as a route during FEB2007-FEB2008, so searching orig airport CLE & destination airport ATL for that time period shows the percent of flights late:

DL 16.95
EV 31.86
OH 52.50
OO 11.25
XE 19.57