"Congestible" refers to something that is susceptible to getting clogged or obstructed. Its antonyms would be "uncrowded," "spacious," "roomy," "unobstructed," and "unrestricted." These terms suggest an environment or area that is free from traffic jams, blockages, or overcrowding. In contrast to congestible, these antonyms convey a sense of ease, freedom, and openness. For instance, an uncrowded highway provides a smooth, uninterrupted ride, whereas a congested one is prone to delays and congestion. Similarly, a spacious office offers ample room for movement and functionality, while a congestible one is hindered by clutter and obstruction.