Obon is a Buddhist event to hold memorial services for ancestors usually from August 13 through 16. During this time the spirits of the dead are believed to return to their former homes and families.
People light lanterns to guide the spirits and perform bon dances to entertain their spirits. On the night of 15th or 16th, people light farewell bonfire or float lanterns on the water to see off the spirits.
The week of obon is considered bon vacation, and many people return to their hometowns or take trips. The heavy traffic congestion is also the seasonal thing.
Even though the times are changing, I hope the heart of this tradition should be observed.