turtarrier
The main purpose of a turtarrier is to keep cars from moving too far forward in a parking space. They're mostly unnecessary if all spaces are facing a sidewalk with a curb, but when two parking spaces are facing towards one another their purpose is made more clear. By clearly defining the depth of a parking space they prevent anyone from taking up two at once if they pull too far forward in the space. They also allow some control over movement throughout a parking lot. Without turtarriers, people who are in a hurry are sometimes inclined to cut across the lot, instead of following the intended paths. By including turtarriers and preventing this sort of behavior, traffic in a lot becomes more predictable, and thus is safer to navigate.