Circumstances when a public good may take on some characteristics of a private good and become a quasi-public good
A quasi-public good starts out like a public good but loses one of its key features under certain conditions. Congestion or new technology can make it rivalrous or excludable — pushing it closer to a private good.
Real World
London's M25 motorway is normally open to all drivers at no cost, but during rush hour congestion makes it rivalrous — one extra car slows everyone else, pushing it toward a private good.
Exam Focus
When asked to 'explain', always state which characteristic (non-rivalry or non-excludability) is lost and why.
Price Elasticity of Demand
PED = % change in quantity demanded ÷ % change in price
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