Why is my power data so much higher for the track versus training on the road

Calibrate the SRM once a month so I am pretty confident of the recorded data. There is a drivetrain loss due to the SRM measuring at the crank and the PowerTap measuring at the hub but this should only account for either about 3% or 15-20 watts depending upon who you believe. This still leaves about a 15% difference. When I have attempted to do intervals on the road I have not come close to what I have done in some of these short track races. Today was the first longer interval day after a week off due to overtraining and another week off due to work traveling. I forgot to use the inhaler so I have to repeat this next week to see if the data holds up or I get better. I started off with a fifteen minute effort up Page Mill to just past Moody where it starts going downhill again. Then I tried a couple of repeats on Moody to see how hard I could push myself. The first time I got 255 watts for about six minutes which I've done before. The second time another ride came by me just as I was starting my interval. This motivated me to go pretty hard at the start and I averaged 278 watts for six minutes which, lowly as it is, is a new personal record for myself on such an interval on the road. I have to conclude I need a rabbit for my intervals or find a new way to motivate myself on these. These also hurt a lot, breathing wise. May take a different approach to training more harder shorter intervals and less longer aerobic efforts. From what I know, most of the faster guys have their FTP way higher than I can hope to raise mine.

72kg