Intercity passenger transportation is a time- and energy-intensive activity. Despite a growing social consciousness of “green” alternatives, travelers continue to choose routes and modes primarily on the basis of travel time and cost. Although long-distance trips of more than 500 mi (800 km) are dominated by air travel, short- and medium-haul trips compete with surface modes when total travel time and cost are compared. Because of hub-and-spoke air transport networks, short-haul air travel is bundled with long-haul itineraries. At congested hubs, passengers can experience lengthy transfer times, which can provide an opportunity for competitive mode substitution. This paper focuses on the travel time trade-offs between air and surface modes and the implications for short-haul air trip substitutability through an analysis of 17 short-haul markets transferring through O'Hare International Airport, Chicago, Illinois. The results suggest that when transfer times are considered, mode substitutability is not directly associated with distance and that there are competitive opportunities for ground modes that may offer cost, energy, and environmental benefits.