When a race track is certified by the RRCA or USATF, it is measured by the shortest route a person can run and stay on the track.
When most people run, they take the most convenient route through the course that they can, which is not necessarily the shortest. Ignoring the inherent inaccuracies of handheld GPS devices, you could actually run up to 27 miles during a marathon as the mile markers go further and further than where your watch tells you it should be.
If you want to run a faster time, it makes sense to try to run the shortest route possible. The way you do it is run on tangents.
What is a tangent?
From Wikipedia: In geometry, the tangent line to a curve at a given point is the straight line that “just barely touches” the curve at that point. As it passes through the point of tangency, the tangent line “goes in the same direction” as the curve, and in this sense is the best straight-line approximation to the curve at that point.
What this means is that instead of following the curve of a road or the course of the race, you should aim directly at the Following curve that comes into view and only run along the curve when you can’t see the next curve until after you’ve passed the current one.
During training, it is appropriate and safer to run along a roadside as this will help you avoid being hit by a car.
However, during a race, you want to run as straight as possible from one corner or around to the next. You’ll cover the same distance (by road) in less time because you won’t have to travel as far (in actual distance).
You can see that on any given set of turns, traversing the tangent is not that much shorter following the edge of the course. However, over the full distance of a race, especially one with lots of twists and turns, it can really add up.
However, don’t take this to mean that you have to hit tangents blindly.
If there are potholes or other roadside obstacles, you may want to turn around, even if it means running a little farther.
In a crowded race, you may not be able to run tangents in the pressure of all the other runners. Even if there are only 1 or 2 people around you, you still have to be careful not to run into someone or cut them off and make them meet you.
Also, make sure you pay attention to course markings and pre-race instructions. Even if a road has a turn, the course itself may not allow you to cross the yellow line on a road, for example.
And as always, please respect the traffic, whether it is allowed on the course or not. If you cross the road in front of a vehicle and hit it, then a car will almost always win and a bike will usually win. Most vehicles are much less maneuverable than you and you risk losing more, so you are always in the corridor to avoid getting hit.
Try this simple strategy the next time you run. You can save seconds on a shorter race or even minutes on a longer race, helping you get to the finish line faster with exactly the same effort.