Fartlek. That's my training plan. The no-plan training plan.

And it suits my terrain, which is mostly rollers. Some days I'll loaf along the flats and downhills, then put all the effort into the short, steep climbs for 30 seconds to 2-3 minutes (which pretty well mimics typical fast club B-group rides, where some folks coast downhill, piddle-pedal flats, and punch up every climb). Other days I'll sprint on the flats and downhills and loaf uphill.

Just depends on how I feel that day, weather and wind, etc.

If you ride with friends who are kinda-sorta competitive, you're probably already doing fartlek training, mixing casual riding with the occasional impromptu sprint just to liven things up or catch a buddy off guard.

If I do regimented timed intervals at all it's on the indoor trainer. The terrain here doesn't lend itself well to that.