Final answer:
The travel cost method struggles to estimate the economic value of highly unique sites due to a lack of comparable sites and failure to account for non-use values.
Step-by-step explanation:
One limitation of the travel cost method (TCM) is that it can be poor at estimating the economic value of a site that has highly unique attributes that are not found in other sites. The travel cost method typically requires comparison with other sites to help estimate consumer surplus and site demand. Yet, if a site is highly unique, fewer or no comparable sites may exist, making it difficult to accurately assess its value using this method. Furthermore, TCM often underestimates the value since it does not capture the non-use value, such as the value people place on simply knowing that a unique site exists, even if they never intend to visit it.