Checkpoints are controlled by Israeli soldiers, who determine how many Palestinians can pass and how long they must wait before they can get through.
As a humanitarian measure, the army erects corrugated metal shelters at some permanent checkpoints to protect waiting Palestinians from the summer sun and rain in winter.
Waiting times vary greatly, depending on the security situation. Sometimes people pass with hardly any delay; at other times they may have to wait an hour or more before being called through.
Sometimes checkpoints are closed altogether.
"Everything is done to allow for quick flow of people through the checkpoints," an Israeli Defense Force spokesman told BBC News Online.