Lower default threshold for skipped failed choices to 0.1%

activitysim/core/configuration/top.py

@@ -790,7 +790,7 @@ def _check_store_skims_in_shm(self):
     .. versionadded:: 1.6
     """
 
-    fraction_of_failed_choices_allowed: float = 0.1
+    fraction_of_failed_choices_allowed: float = 0.001
     """
     Threshold for the fraction of households that can be skipped before failing the model run,
     used in conjunction with `skip_failed_choices`.

docs/dev-guide/changes.md

@@ -14,6 +14,31 @@ branch (i.e., the main branch on GitHub), but not yet released in a stable versi
 of ActivitySim.  See below under the various version headings for changes in
 released versions.
 
+### Skipping Failed Choices
+
+A new feature is introduced to ActivitySim to skip failed choices during model execution. 
+By default, ActivitySim will skip any failed choices during a model run, i.e., `skip_failed_choices` is set to `True`. 
+A failed choice occurs when the computed utilities for all alternatives are zero, or infinite, or nan, which can happen due to 
+data issues or model specification problems. A warning message is logged when a failed choice is encountered, 
+and the corresponding household (along with its persons, vehicles, tours, trips, etc) will be excluded from further model steps.
+At the end of the model run, a summary of all skipped households is provided in the log file for user reference. Users can set
+a threshold for the maximum allowed percentage of skipped households `fraction_of_failed_choices_allowed`, 
+and if the percentage of skipped households exceeds this threshold, 
+the model run will be terminated with an error. The default threshold is set to `0.001`, 0.1% of households. 
+
+This feature helps to ensure that the model can continue running even in the presence of data or specification issues, 
+while also providing visibility into such issues that need to be addressed.
+See more information in ActivitySim's users guide "Skip Failed Choices" and code updates in [PR #1023](https://github.com/ActivitySim/activitysim/pull/1023)
+
+##### Potential Impact on Existing Model Runs:
+
+With `skip_failed_choices` defaulted to `True` and an allowed failure threshold defaulted as 0.1% of households, 
+failures that were previously silently masked will now generate warnings, be explicitly skipped, and counted toward the threshold. 
+As a result, model runs that previously completed "successfully" may now fail earlier, 
+surfacing underlying specification or data issues that require attention rather than being silently absorbed. If an agency does not
+want to address the underlying issues immediately, they can set `skip_failed_choices` to `False` to maintain the previous model results, 
+but it is recommended to review the log file for any warnings about failed choices and address them as soon as possible to ensure model quality.
+
 ### Shadow Price Zones Reopening
 
 We fixed an issue with reopening work and school zones during iterative shadow pricing using the

docs/users-guide/ways_to_run.rst

@@ -312,6 +312,11 @@ For interaction_simulate models, users can manually specify trace IDs to perform
 Users can configure ActivitySim to not skip failed choices by setting the 
 ``skip_failed_choices`` option to ``False`` in the settings file. When this option is disabled, the system will fall back to
 using the legacy ``overflow_protection`` mechanism to handle such cases. Specifically, if the computed utilities lead to zero or infinite exponentiated values, 
-overflow protection will adjust the utilities to prevent numerical overflow during exponentiation and arbitarily making a choice. 
-No loggings will be made for these cases. When ``skip_failed_choices`` is enabled, 
-ActivitySim will not use the legacy ``overflow_protection`` mechanism to handle failed choices.
+the legacy ``overflow_protection`` will adjust the utilities to prevent numerical overflow during exponentiation and arbitarily making a choice, however, no loggings will be made for these cases. 
+When ``skip_failed_choices`` is enabled, ActivitySim will not use the legacy ``overflow_protection`` mechanism to handle failed choices.
+
+.. note::
+  When an agency turns on ``skip_failed_choices`` for the first time in an existing ActivitySim implementation, 
+  warning messages may appear in the log for failed choices that were previously handled silently by the legacy ``overflow_protection`` mechanism. 
+  These warnings are expected and reflect the change in behavior: failed choices are now explicitly skipped and traced rather than silently handled. 
+  In some cases, model runs may crash if the number of skipped failed choices exceeds the configured ``fraction_of_failed_choices_allowed`` threshold.