He was leaning on the stone wall of the bridge, smoking a cigarette and watching the cars speed by on the highway beneath him.

Adam has just bragged about beating somebody up at the mall. This sentence establishes the story’s setting, and most of the story takes place here, on the bridge. The stone wall suggests sturdiness and safety. The bridge provides distance from the cars and the consequences of Adam’s bad behavior. The words “beneath him” also suggest Adam’s attitude towards other people. He is literally and figuratively elevated above them.

Seth leaned forward and felt the smooth cold granite of the bridge with his fingers. The bridge was old and made of large granite blocks. Its heavy stone abutments stood close to the cars that sped past on the highway beneath it.

The narrator describes the bridge where Adam and Seth loiter. The bridge is solidly built with granite, which accounts for its longevity. The abutments, also made of stone, support the bridge on both sides. The sturdiness of the abutments and their closeness to the road adds an element of danger to the story. Adam’s reckless behavior could cause a serious accident if a driver were to swerve into one of them.

The two boys looked back down at the highway. It was a warm, spring afternoon, and instead of taking the bus home after school they'd decided to walk to the diner.

The bridge offers the boys a vantage where they can look down on the world around them. This prospect reflects Adam’s sense of superiority and provides Seth with a sense of safety. The weather also seems idyllic, and the season suggests new beginnings and transformations. Seth wants to change himself to be more like Adam. However, the pleasantness of the day is marred by Adam’s increasingly risky behavior and the violence that follows.

Neither of them saw the black car pull off onto the exit ramp and come up behind them on the bridge. . . . Seth suddenly decided it was time to go, but he quickly realized that the three guys had spread out, cutting off any way to escape. He and Adam were surrounded.

The bridge has given Adam a false sense of security, allowing him to taunt and terrorize the cars below while believing himself safe from any consequences. However, the highway below has a nearby exit ramp, which the bullies in the black car take. With only two exit points, the seemingly safe bridge becomes a trap when the bullies surround the boys.