Many distances (5K, 10K, etc.) are given in kilometers.
DAVE MCGILLIVRAY, for Runner's World
Why are courses marked in miles instead of kilometers? Aside from marathons and halfs, many race distances are promoted in kilometers (5K, 10K, 15K, etc.). I train, as most runners do, on a 400-meter track, and all my training is done in kilometers. What’s with the hang-up on English measurements? —Joe
Excellent question. It would be interesting to survey all the runners in a big race and see what the majority would prefer. All your points are indeed well taken, and, for sure, you are not alone. However, my sense tells me that the majority of participants in races today would still prefer mile markers instead of kilometer markers. I know I would. Take a poll yourself and see what runners of all abilities in your area would prefer.
It is important to note what most who watch and follow the sport in the United States are accustomed to and can easily understand. I know the world has moved towards the metric system, but I wonder how much the U.S. has followed—a larger debate we don't have the space to go into here.
I don't think many race directors will soon abolish the mile markers and replace them with kilometers. Some of us use both, but not everyone. In the Boston Marathon, we mark every mile and every 5-K. Additionally, we mark every kilometer in the first 10-K of the race, but not the entire way. This way, those who are strictly using the kilometer measurements can judge their pace early on.
Why don't we place markers and clocks at all of the mile and kilometer locations? Well, that, combined with the half-marathon mark and, say, a one-mile-to-go mark, would mean we would have up to 70 markings on the course, which would need signs and/or clocks and/or volunteers. That is a lot. As such, most race directors pick one or the other, and it seems like the mile-marking system remains in the lead of this race.