diff --git a/activitysim/abm/models/util/mode.py b/activitysim/abm/models/util/mode.py
index 49776684a..d82dd09ea 100644
--- a/activitysim/abm/models/util/mode.py
+++ b/activitysim/abm/models/util/mode.py
@@ -88,7 +88,8 @@ def mode_choice_simulate(
     choices[mode_column_name] = choices[mode_column_name].map(
         dict(list(zip(list(range(len(alts))), alts)))
     )
-    cat_type = pd.api.types.CategoricalDtype([""] + alts.tolist(), ordered=True)
+    # note: do we want to order the mode categories?
+    cat_type = pd.api.types.CategoricalDtype([""] + alts.tolist())
     choices[mode_column_name] = choices[mode_column_name].astype(cat_type)
 
     return choices
diff --git a/activitysim/abm/models/util/school_escort_tours_trips.py b/activitysim/abm/models/util/school_escort_tours_trips.py
index 4a9f2ef17..665844023 100644
--- a/activitysim/abm/models/util/school_escort_tours_trips.py
+++ b/activitysim/abm/models/util/school_escort_tours_trips.py
@@ -767,7 +767,9 @@ def merge_school_escort_trips_into_pipeline(state: workflow.State):
             if isinstance(school_escort_trips[c].dtype, pd.api.types.CategoricalDtype):
                 from pandas.api.types import union_categoricals
 
-                uc = union_categoricals([trips[c], school_escort_trips[c]])
+                uc = union_categoricals(
+                    [trips[c], school_escort_trips[c]], sort_categories=True
+                )
                 trips[c] = pd.Categorical(trips[c], categories=uc.categories)
                 school_escort_trips[c] = pd.Categorical(
                     school_escort_trips[c], categories=uc.categories
diff --git a/activitysim/core/util.py b/activitysim/core/util.py
index 940796e4b..d7d0766a0 100644
--- a/activitysim/core/util.py
+++ b/activitysim/core/util.py
@@ -340,6 +340,24 @@ def assign_in_place(df, df2, downcast_int=False, downcast_float=False):
     common_columns = df2.columns.intersection(df.columns)
     if len(common_columns) > 0:
         old_dtypes = [df[c].dtype for c in common_columns]
+        # in pandas 2.x, update a categorical column with any new categories will cause TypeError
+        # so we need to add the new categories first
+        # this is a workaround for pandas 2.x, see discussion in
+        # https://github.com/ActivitySim/activitysim/discussions/946
+        for c in common_columns:
+            if isinstance(df[c].dtype, pd.CategoricalDtype):
+                if not isinstance(df2[c].dtype, pd.CategoricalDtype):
+                    # if df column is categorical, but df2 column is not
+                    # convert df2 column to categorical then union categories
+                    df2[c] = df2[c].astype("category")
+
+                # when df and df2 column are both categorical, union categories
+                from pandas.api.types import union_categoricals
+
+                uc = union_categoricals([df[c], df2[c]], sort_categories=True)
+                df[c] = pd.Categorical(df[c], categories=uc.categories)
+                df2[c] = pd.Categorical(df2[c], categories=uc.categories)
+
         df.update(df2)
 
         # avoid needlessly changing int columns to float
@@ -426,7 +444,7 @@ def auto_opt_pd_dtypes(
                 else:
                     df[col] = pd.to_numeric(df[col], downcast="float")
         # Skip if the column is already categorical
-        if pd.api.types.is_categorical_dtype(dtype):
+        if isinstance(dtype, pd.CategoricalDtype):
             continue
         # Handle integer types
         if pd.api.types.is_integer_dtype(dtype):
diff --git a/activitysim/core/workflow/state.py b/activitysim/core/workflow/state.py
index 45aa7a1f7..50ba0342a 100644
--- a/activitysim/core/workflow/state.py
+++ b/activitysim/core/workflow/state.py
@@ -1099,7 +1099,9 @@ def extend_table(self, table_name, df, axis=0):
                         if isinstance(df[c].dtype, pd.api.types.CategoricalDtype):
                             from pandas.api.types import union_categoricals
 
-                            uc = union_categoricals([table_df[c], df[c]])
+                            uc = union_categoricals(
+                                [table_df[c], df[c]], sort_categories=True
+                            )
                             table_df[c] = pd.Categorical(
                                 table_df[c], categories=uc.categories
                             )