There are different types of stacking that ICS uses to keep control of the stack and maintain the order of washes purchased.

Stacking Loop is recommended by ICS. Using the Stacking Loop ensures that the cars entering the wash are doing so in the correct order.

Non-Stacking Loop is used in locations where either the Stacking loop is not functioning, or it does not make sense to use a Stacking loop due to the site layout.

An example of where not to use a stacking loop would be if there is no clear area before the tunnel where vehicles cannot pass one another, forming a single file line.
In a Non-Stacking Loop setup, the Stacking loop is not hooked up or does not exist all together. We would need to use the Gate Loops as the Stacking Loops. Both types of Gates have the ability to send a second signal back to the Auto Sentry to use as a Gate Busy.