Traffic officers decided it was too dangerous to follow them and called for back-up, but were unable to prevent the collision.

He delayed ejecting until he could prevent a collision with a nearby occupied van.

Movement of trains operating against the established flow of traffic would still require train orders or other special manual protections to prevent a collision.

By the time it became clear that there was a significant problem, it was too late to prevent the collision.

Both captains realized the other ship was near, and had ordered the engines reversed, but it was too late to prevent a collision.