What is a significant factor that influences air carriers' route selection?

The economic drivers of the flying public play a significant role in air carriers' route selection as they directly impact demand for air travel. This encompasses factors such as the economic status of a region, population income levels, employment rates, and overall economic activity. Carriers are more likely to establish routes that connect to destinations with robust economic activity, as these routes are expected to generate higher passenger volumes and revenue.

For example, if a city's economy is thriving, with strong business and tourism sectors, airlines will prioritize routes to and from that city to capture the increased demand. Moreover, understanding the economic dynamics helps airlines to forecast travel trends and determine which routes would be more profitable based on passenger travel patterns influenced by economic activities.

Considering the other options, while they may contribute to route planning, they do not hold as much weight in influencing air carriers' decisions. The distance to the nearest city, overall tourist traffic in the region, and the size of the airport terminal may impact logistics and operational factors but are secondary to the underlying economic motivations that drive consumer travel behavior.