4. Time Trial Series
If your city offers a time trial series, you can use the time trials as workouts and as markers of improved performance. This is similar to the self-designed, as-fast-as-you-can-go time trial, but with other racers serving as additional motivation.
5. Other People in a Group Ride
Other riders can be can be used as markers of improvement; but you have to be a little careful with this marker. If you measure your performance against some of the best riders in your group ride and on one particular day you are able to keep up with these riders it can be a marker for improvement. That written, the top riders may be under the weather which makes it a somewhat shallow victory. Or, those riders may make excuses for their sub-par-compared-to-you performance. Those excuses may or may not be valid. Your performance may well be improving but other riders don't want to acknowledge your success.
6. Data From the Group Ride
My preference is to pair marker #5 with data from your computer. Does the data on your computer note higher average speeds or average power output for particular time segments? How does your heart rate track compared to power output -- is it lower for a given power output?
7. Single Ride Endurance
If an athlete is looking to build endurance, one of the markers I look at is long ride time. How long can you ride now, compared to two or three months ago?
8. Weekly Training Time
When building endurance, I not only look at a single ride duration, but I also look at weekly training volume. Is the athlete handling more training volume than a few months ago?
9. Volume of Training Intensity
If training volume is steady, or slightly building, is the volume of intensity increasing and is the athlete successfully handling the load?
10. How Do You Feel?
Is your perceived exertion going down for a given distance or workout? Sometimes the data doesn't show improvement, but the athlete feels stronger and more confident. This measure should not be underestimated.
If your training is heading in the right direction, based on several measures, and you have a less than desirable performance on race day, then chalk it up to a bad day on the bike.
If your training is not showing you are moving in the right direction, making progress toward your goal, time to change something about your training.