Why might quasi-public goods blur the line between private and public goods?

Quasi-public goods blur the line between private and public goods because they possess characteristics of both types.

Quasi-public goods, also known as semi-public goods, are goods that are not fully non-excludable and non-rivalrous, which are the defining characteristics of public goods. They are not fully excludable because it is difficult, but not impossible, to prevent people from using them once they are provided. They are not fully rivalrous because their consumption by one person does not significantly reduce the availability for others, but there may be congestion effects if too many people use them at the same time.

For example, a toll road is a quasi-public good. It is non-excludable because once it is built, anyone can use it. However, it is not completely non-rivalrous because if too many people use it at the same time, it can become congested. Similarly, a public park is a quasi-public good. It is non-excludable because anyone can use it, but it can become congested if too many people use it at the same time.

On the other hand, private goods are both excludable and rivalrous. They are excludable because people can be prevented from using them if they do not pay for them. They are rivalrous because their consumption by one person reduces the availability for others. For example, a chocolate bar is a private good. It is excludable because you can prevent someone from eating it if they do not pay for it. It is rivalrous because if one person eats it, there is none left for others.

Therefore, quasi-public goods blur the line between private and public goods because they possess characteristics of both. They are not fully non-excludable and non-rivalrous like public goods, but they are not fully excludable and rivalrous like private goods either. This makes them a unique category of goods that can be difficult to classify.