Course Difficulty Rankings

We walk each course’s GPS route in ~400-meter windows and apply our grade-adjustment model to every window: uphills cost about 12 seconds per mile for each 1% of grade; downhills give back less than they take (about half on gentle grades), and past -6% the benefit shrinks further because braking forces take over. Sampling at 400 m matters — mile-average grades let rolling hills cancel out and hide their cost.

Courses above 1,500 m elevation get an altitude penalty of 2% per 1,000 m — thinner air slows everyone. The terrain and altitude costs sum to a total time cost versus a flat sea-level course, expressed for a reference runner at 4:00-marathon pace (9:09/mi), then mapped to a 0-100 index where dead-flat sits at 20.

The index scores the course profile only. Weather, field congestion, and how the hills are sequenced (Boston’s late Newton hills after quad-pounding descents) are modeled separately in each course’s race planner.