patch-ahead reports the single patch that is the given distance ahead of the asking turtle. You can think of it as the turtle looking at a patch in front of it. For example, if we were creating a highway traffic model and wanted our cars to only move if there was no other car in front of them, we would write the following code:

ask cars [
    set heading 90
    if count turtles-on patch-ahead 1 = 0 [
        forward 1
    ]
]

Things to keep in mind when using patch-ahead:

• In some cases when a model's world is not wrapping, patch-ahead may report nobody and lead to an error because a patch may not exist. We can avoid this error by using an if statement like if patch-ahead 1 != nobody [ forward 1 ].
• We can provide floating point numbers to patch-ahead, as well as integers, such as patch ahead 2.76.

In the model example below, we have some gray patches that represent a road and a red patch that represents a stop sign. Our car moves on the road towards east as long as the pcolor of the patch-ahead 1 is gray. If not, our car does not move, which means that it stops at the stop sign.