Unpacking “Carrying Capacity”​ and “Carrying Plans”

This blog is part 2 of a series on managing visitor flows for World Heritage Sites (WHS). Read Part 1 here, Part 2 here, Part 3 here, and Part 4 here.

Carrying capacity is an important but often misunderstood concept in managing and preserving sites. Misunderstanding it as simply how many persons can fit into a space could result in damaging the site or dissatisfied visitors. Meanwhile, using static, space-only-based calculations could inflate the number of visitors allowed in a facility beyond its true capacity. So setting the carrying capacity right is crucial. If the carrying capacity is set low, the site will lose revenues, as visitors will need to be turned away. If, on the other hand, the carrying capacity is set too high, there won’t be enough resources to monitor the security of the site, and the site can be damaged.

But what does carrying capacity fully entail?

In its most basic terms, carrying capacity means the maximum number of visitors a site can handle using full “resources” (i.e. personnel, ticketing booths, kiosks, etc.) and without damaging the site. Looking at its meaning, its importance can be understood: by understanding what a site’s carrying capacity is, one can understand how many visitors the site can “truly” handle.

Figure 1: Visitor Access vs. Site Preservation Trade-off Chart

The chart above depicts the relationship between visitor access and site preservation. Traditionally, it’s understood that as visitor access volume (i.e. number of visitors) increases, potential damage to the site increases. However, this traditional wisdom is not necessarily always true. Increasing the visitor access up to the correctly calculated carrying capacity with an optimized “carrying plan” (i.e. correctly calculated carrying capacity with optimal resources and accompanying people flow processes) will yield a win-win solution.

Static analyses (commonly known as Fruin analyses) are often unable to calculate the carrying capacity of a World Heritage Site (WHS) because they only consider the square footage required per person based on the action performed by the visitor. This type of analysis may be useful in determining the maximum persons that can be accommodated on a train platform or in a large hall. But a WHS visitor has more sophisticated needs due to the nature of a WHS: firstly, the site is more prone to damage, and when damaged, cannot be replaced. Secondly, visitors are engaging in an “interactive” experience, usually with the use of actual tour guides, or audio-guide equipment, and tend to take their time in certain areas.

While many architects use static analyses to calculate site carrying capacity, this type of analysis doesn’t take into account all the other components of a WHS site, from entry to exit operations and the resources necessary to serve visitors. Thus, when determining the carrying capacity of a WHS, it is important to understand that the sites’ “components” or spaces have their own, separate carrying capacities. Hence, the carrying capacity of the whole site is the outcome of how these components are used at different times. To demonstrate this idea of separate carrying capacities and how they interact with the overall carrying capacity, let’s examine China’s Mogao Grottoes site.

The Mogao Grottoes, located in the Western Province of China, are a fragile historical site operated by UNESCO. Numbering around 735 caves, the Grottoes are live archaeological sites where visitor flow must be carefully and mindfully controlled. The site can carry up to 3,000 visitors when all the “must-see” caves are included in the tours. However, it’s carrying capacity can increase to 6,000 visitors per day by limiting visitors to 4 minutes in some of the “must-see” caves. This capacity can even go above 6,000 if some of the “must-see” caves become “optional” (i.e. require a special ticket).

In the example above, we can see that the site’s carrying capacity increases and decreases according to the number of visitors who visit the “must-see” caves. Management can control carrying capacity for the whole site by simply controlling the number of visitors who see the more famous caves. This can be done by, for example, making these caves cost an additional fee. At WHS, carrying capacity is more than a static variable in visitor flow operations. It is one factor, out of many, that can and should be “adjusted” according to visitor flow needs.

As previously discussed in this blog, an organization should plan for “forecasted demand” rather than daily averages in order to effectively manage visitor experience. The same can be said of carrying capacity. Instead of planning for the site’s carrying capacity, organizers should develop a “carrying plan.” This plan should specify what actions might be needed to achieve different visitation volume goals. In the case of the grottoes, higher ticket prices for the “must-see” caves could be one strategy for a carrying plan that serves to control the high peak visitor days. This carrying plan should also include carrying capacity targets with time dependencies. For example, let’s say a carrying plan allows visitors to see all the caves when the daily visitor volume is forecasted to be less than 10,000. But when the visitation volume exceeds 10,000, the plan calls for limiting access for the must-see cave access to certain ticket holders or, alternatively, letting “regular” visitors see only a subset of must-see caves, while alternating the caves for different groups. This type of strategy is essential to a carrying plan, because unless one controls the entrance into every part of a site, it is inevitable that there will be more visitors in certain areas at different times. Thus, a carrying plan must take into account the probability of having a variable number of visitors over time in a particular area.

An optimized carrying plan with a correctly calculated carrying capacity is key when maximizing the visitor satisfaction levels of a site. Because of a WHS’s dynamic nature, the interaction between the site’s different components, resource levels, variability in demand and carrying plans should be optimized using a modeling approach such as simulation. Careful consideration and planning will allow for appropriate resource allocation and better management, especially on days when visitors are in large numbers. But what number, or rather what kind of day, should an organization base its calculations on? Read our next post to find out more about making a “design day” and peak demand management.

Stay up to date KCG’s blogs here and to explore visitor management practices, check out our previous blog.

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