I am having a hard time understanding why my commute is taking as long as it is. It is taking me about an hour to travel 11.4 miles.

I commute on my Specialized Tricross that has 32c T-Serv's tires on it (always at the correct pressure). I basically have a straight shot to work with only a few lights over the course of the commute (and can usually hit them green in the morning) and very little in the way of elevation gain/loss (the whole trip is along Pacific Coast Highway). I travel faster than most of the mountain bikes I encounter, but slower than the roadies. It seems like my average speed should be above 11.4 mph for the type of bike I am riding.

My only guess is that I am unknowingly slowing down during certain points of my commute. Does anybody else run into this problem and if so how have you overcome this issue? Would a cadence meter help with this?