A compound curve is a curve that tightens part way through. These layouts can be particularly dangerous for motorcyclists because riders often select their speed and line based on the first curve radius. When the curve suddenly tightens, there is very little time or traction available to correct. The natural path is often toward the outside of the curve (into the opposing lane or roadside).
In this video you can see the curve tighten, creating a situation where the rider drifts into the opposing lane.
Addressing this risk can be challenging, but potential treatments include:
- Smoothing out the compound nature of the curve (although this can be very expensive)
- Clearing vegetation and other sight obstructions to improve visibility of the tighter radius ahead
- Using speed advisory signs based on the second curve radius
- Installing Compound Curve (Curve Tightens) warning signs (see Safe System Snippet #16)
- Applying perceptual countermeasures to encourage lower approach speeds and improve lane positioning (interestingly, some of these can already be seen in the opposing direction in the video below)
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