Editing Automatic Warning System (section)

=== Limitations ===
This list of limitations is not exhaustive:

* The AWS only has two output states; a clear indication and a warning indication. For warning indications, AWS does not provide any extra information about the reason for the warning. It is therefore reliant on the driver to observe the surroundings and determine the reason for the warning indication.

* AWS warning indications require the AWS acknowledge button to be pressed by the driver. It is possible for a driver on a crowded suburban railway to run all day on caution aspects, acknowledging hundreds of AWS warning indications. Continually acknowledging AWS warning indications can lead to a state where the driver fails to take appropriate action. This has led to a number of fatal accidents{{fact|date=March 2023}}.

* It is possible for AWS to develop a [[wrong-side failure]] and the driver is given either no indication or a clear indication instead of a warning indication. The handbook notes that "AWS does not relieve the driver of the responsibility of observing and obeying lineside signals and indicators."<ref name="Awsrules"/>

* There is also no special treatment of stop signals. A driver can still pass a stop signal aspect [[Signal_passed_at_danger|(SPAD)]] if they acknowledge the AWS warning indication. Other protection systems such as the [[Train Protection & Warning System|Train Protection & Warning System (TPWS)]], can overcome this limitation.