The antonyms for the word "over passes" are "underpasses" or "tunnels." These structures are designed to allow traffic to pass beneath an obstacle or through a mountain instead of over it. Unlike overpasses, underpasses are often safer for pedestrians and cyclists as they can continue their journey without being hindered by vehicular traffic. Tunnels, on the other hand, can be used to avoid steep inclines or mountainous terrain, allowing for a smoother and more efficient flow of traffic. Both underpasses and tunnels serve as excellent alternatives to overpasses, providing a safer and more effective means of transportation.