We completed the measurement rides for the new People's United Bank Vermont City *Half* Marathon & Relay course last weekend. This work is done to meet the USA Track & Field (USATF) standards for a certified course. Before we get to race day, we would like to alert all fitness watch wearers that it is nearly certain that your Garmin/Polar/Timex/phone app is going to tell you you ran farther than 13.1 miles on the 24th.
We always get a bunch of emails, calls, and social media shout outs from runners who tell us our course was long. We appreciate your messages, and we always investigate them, but we’ve never found an instance at the Vermont City Marathon where the course was actually long, as per what USATF requires.
That said, there are certainly instances when races get the distance wrong. It happens! Cones get placed incorrectly, volunteers make a mistake and direct runners the wrong way, an emergency requires a course re-routing. All the planning in the world can’t help human error some times. We had it happen many years ago at our New Years Day 5k, where a lead vehicle made a mistake and turned one block early mid-way through the race. That cut off about .15 miles and turned a 5k into a 2.95 mile race. We acknowledged that error, went out to measure the difference, and published a chart showing how much time a racer would have saved at different paces.
There are a number of reasons why your race will get recorded long by your GPS as compared to the official certified course:
- The biggest reason is that courses are measured on strict tangent lines around the course. Racers almost never run the true tangents! Even if it’s just to veer from one side of the road to the other to grab a cup of water, that is adding distance. On 90° corners you can add a lot of distance compared to the official measurement. On a 90° city block, a typical “2 lanes plus parking” road, if a runner stays in the middle of the street vs running to the inside corner, that runner will add about 35 feet to their race. 35’ isn’t much, but do that on 4 or 5 corners and you’ve added almost .03 miles to your race.
- The “Short Course Prevention Factor”… Here’s an element that you are probably not aware of. In order to virtually guarantee that all road race courses are at least the distance they are advertised to be, USATF requires measurers to add .1% when we do our work. That’s 5.28’ per mile, or about 69’ over a half marathon. Even if you are running perfect tangents and your GPS is working perfectly and gets an unobstructed clear signal throughout the race, you will notice that your watch beeps a little before each mile. And of course that gets amplified as you move along a course. At mile 10, you can expect your watch to beep about 53’ before the official Mile 10 sign.
- Consumer Grade GPS accuracy… The GPS on your wrist or in your watch is built to be accurate to within about 5 meters at any given point, and many times it will be even more accurate than that. When you’re moving, they do a good job of tracking your route, but it can be off by a bit at any given time. Those positioning errors add up, and can be significant. Here’s a good experiment to try… Go to your local track and run 2 miles in the inside lane. Download your running route. Nearly every time it’s going to show part of that run will be inside lane 1, and part will be out in lanes 3-4-5, even though you stuck right to lane 1. Completing a lap in lane 4, as opposed to lane 1, adds over 75’.
- GPS interference… The watch on your wrist and your phone can sometimes have trouble picking up a GPS signal due to big buildings, underpasses, tree cover, etc. In that case, GPS guesses as to where you are.
These are the main reasons why your watch might say your half marathon was 13.3 or 13.4 miles or more. The first 3 items above will always add distance to your race. The 4th could either add or subtract distance, depending on when the interference kicked in and when you picked the signal back up. We’ve all been running a lot of Virtual races over the last 15 months, and we’re used to a half marathon ending when our watches hit 13.1 miles.
Don’t be surprised if you see a bit more than 13.1 on your watch after the 24th. We promise you, we've accurately measured this course to be on par with USTAF standards for a certified half marathon course.