Last week's answer

Question: If you've driven on modern interstates, you've likely noticed flexible steel cable barriers running along narrow grass medians instead of traditional rigid concrete W-beam guardrails. Despite looking much lighter and thinner than concrete walls, high-tension cable barriers are remarkably effective at stopping cross-median head-on crashes. What key physical mechanism allows these steel cables to absorb the massive kinetic energy of an out-of-control vehicle?

Answer: The cables flex up to 12 feet upon impact, catching the vehicle like a net and dissipating energy by bending and breaking lightweight steel line posts.

Minnesota Department of Transportation found these barriers resulted in a 62% reduction in median-related fatal and serious injury crashes. Once the posts break, the vehicle is redirected along the media, preventing a median crossover crash, or stops the vehicle from reentering the roads. 

Source: MnDOT