This isn’t my coldest run ever, but it’s on the list. You can’t afford to get lost in this kind of weather, because you can’t afford to stop running in this kind of weather. Sweat is just too effective at four degrees. Fortunately, the prairie rolls all around me, and it’s hard to get lost when you can see for miles in every direction. There, back in the little town where I have a warm room, I can see the white bulb of the water tower, the nettle of church spires. If I had to, I could veer into the fields of corn stubble and make straight for them—even the tilled earth is frozen as solid as the road. So the goal is not simply survival. I can do better than that. But neither speed nor distance will make a fair measure of the day. The clear, dry cold somehow also has a wicked density that slogs and garbles my stride. It’s alright, there are other challenges to rise to. Can I warm enough of this frigid air to catch my breath? Is this balaclava going to freeze to my face? Can my exertion warm my legs from the inside before the cold works its way into my muscles and slows me to a shuffle? For a few miles there, the cold had the edge, and my metabolism is burning through fuel in a hurry, but for now my exertion is winning out. There’s one other race, however, that I hadn’t considered, though I should have. A rail line, a busy one, runs right through this stretch of prairie. The tracks lie between me and central heating. I can feel and then hear the now-familiar rumble of a train approaching. In this low, flat terrain, that rumble covers many miles, and it’s possible I can make it over the tracks in plenty of time. It’s possible, too, that I can’t. If I were warm enough to really stretch out… but if I were that warm it wouldn’t be any problem to stop and wait for a parade of box and tank cars to trundle past. As it is, if this train outruns me, I will have to turn at the tracks, a hundred yards from home, and set off in some other direction, any direction in which I can keep moving, running against the cold.