diff --git a/docs/modules/io.rst b/docs/modules/io.rst
index 09083d7..0c2d291 100644
--- a/docs/modules/io.rst
+++ b/docs/modules/io.rst
@@ -61,6 +61,8 @@ PostGIS Import
 
 .. autofunction:: trackintel.io.postgis.read_trips_postgis
 
+.. autofunction:: trackintel.io.postgis.read_tours_postgis
+
 CSV File Export
 ===============
 
@@ -89,6 +91,8 @@ PostGIS Export
 
 .. autofunction:: trackintel.io.postgis.write_trips_postgis
 
+.. autofunction:: trackintel.io.postgis.write_tours_postgis
+
 Predefined dataset readers
 ==========================
 We also provide functionality to parse well-known datasets directly into the trackintel framework.
diff --git a/trackintel/io/__init__.py b/trackintel/io/__init__.py
index bc8260f..540233e 100644
--- a/trackintel/io/__init__.py
+++ b/trackintel/io/__init__.py
@@ -30,6 +30,9 @@ from .from_geopandas import read_trips_gpd
 
 from .file import read_tours_csv
 from .file import write_tours_csv
+from .postgis import read_tours_postgis
+from .postgis import write_tours_postgis
+from .from_geopandas import read_tours_gpd
 
 from .dataset_reader import read_geolife
 from .dataset_reader import geolife_add_modes_to_triplegs
diff --git a/trackintel/io/dataset_reader.py b/trackintel/io/dataset_reader.py
index ebb3f2e..5311452 100644
--- a/trackintel/io/dataset_reader.py
+++ b/trackintel/io/dataset_reader.py
@@ -39,6 +39,7 @@ def read_geolife(geolife_path, print_progress=False):
 
     labels: dict
         Dictionary with the available mode labels.
+        Keys are user ids of users that have a "labels.txt" in their folder.
 
     Notes
     -----
@@ -137,10 +138,7 @@ def _get_labels(geolife_path, uids):
     No further checks are done on user ids, they must be convertable to ints.
     """
     labels_rename = {"Start Time": "started_at", "End Time": "finished_at", "Transportation Mode": "mode"}
-    label_dict = defaultdict(
-        partial(pd.DataFrame, columns=["started_at", "finished_at", "mode"])
-    )  # output dict for the labels
-    # TODO: change geolife_add_modes_to_triplegs so that we can use a dict instead.
+    label_dict = {}  # output dict for the labels
 
     # get paths to all "labels.txt" files.
     possible_label_paths = ((os.path.join(geolife_path, user_id, "labels.txt"), user_id) for user_id in uids)
@@ -242,16 +240,13 @@ def geolife_add_modes_to_triplegs(
     # temp time fields for nn query
     tpls["started_at_s"] = (tpls["started_at"] - pd.Timestamp("1970-01-01", tz="utc")) // pd.Timedelta("1s")
     tpls["finished_at_s"] = (tpls["finished_at"] - pd.Timestamp("1970-01-01", tz="utc")) // pd.Timedelta("1s")
-    all_users = tpls["user_id"].unique()
     # tpls_id_mode_list is used to collect tripleg-mode matches. It will be filled with dictionaries with the
     # following keys: [id', 'label_id', 'mode']
     tpls_id_mode_list = list()
 
-    for user_this in all_users:
+    for user_this in labels.keys():
         tpls_this = tpls[tpls["user_id"] == user_this]
         labels_this = labels[user_this]
-        if labels_this.empty:
-            continue
 
         labels_this["started_at_s"] = (
             labels_this["started_at"] - pd.Timestamp("1970-01-01", tz="utc")
@@ -292,10 +287,7 @@ def geolife_add_modes_to_triplegs(
         tpls = tpls.join(tpls_id_mode)
         tpls = tpls.astype({"label_id": "Int64"})
 
-    try:
-        tpls.drop(["started_at_s", "finished_at_s"], axis=1, inplace=True)
-    except KeyError:
-        pass
+    tpls.drop(["started_at_s", "finished_at_s"], axis=1, inplace=True)
 
     try:
         tpls.drop(["ratio"], axis=1, inplace=True)
diff --git a/trackintel/io/from_geopandas.py b/trackintel/io/from_geopandas.py
index 5e101c1..1bb34a1 100644
--- a/trackintel/io/from_geopandas.py
+++ b/trackintel/io/from_geopandas.py
@@ -401,7 +401,12 @@ def _trackintel_model(gdf, set_names=None, geom_col=None, crs=None, tz_cols=None
     if tz_cols is not None:
         for col in tz_cols:
             if not pd.api.types.is_datetime64tz_dtype(gdf[col]):
-                gdf[col] = _localize_timestamp(dt_series=gdf[col], pytz_tzinfo=tz, col_name=col)
+                try:
+                    gdf[col] = _localize_timestamp(dt_series=gdf[col], pytz_tzinfo=tz, col_name=col)
+                except ValueError:
+                    # Taken if column contains datetimes with different timezone informations.
+                    # Cast them to UTC in this case.
+                    gdf[col] = pd.to_datetime(gdf[col], utc=True)
 
     # If is not GeoDataFrame and no geom_col is set end early.
     # That allows us to handle DataFrames and GeoDataFrames in one function.
diff --git a/trackintel/io/postgis.py b/trackintel/io/postgis.py
index 7e2a9de..0746889 100644
--- a/trackintel/io/postgis.py
+++ b/trackintel/io/postgis.py
@@ -579,6 +579,118 @@ def write_trips_postgis(
         )
 
 
+@_handle_con_string
+def read_tours_postgis(
+    sql,
+    con,
+    geom_col=None,
+    crs=None,
+    index_col=None,
+    coerce_float=True,
+    parse_dates=None,
+    params=None,
+    chunksize=None,
+    **kwargs
+):
+    """Read tours from a PostGIS database.
+
+    Parameters
+    ----------
+    sql : str
+        SQL query e.g. "SELECT * FROM tours"
+
+    con : str, sqlalchemy.engine.Connection or sqlalchemy.engine.Engine
+        Connection string or active connection to PostGIS database.
+
+    geom_col : str, optional
+        The geometry column of the table (if exists).
+
+    crs : optional
+        Coordinate reference system if table has geometry.
+
+    index_col : string or list of strings, optional
+        Column(s) to set as index(MultiIndex)
+
+    coerce_float : boolean, default True
+        Attempt to convert values of non-string, non-numeric objects (like
+        decimal.Decimal) to floating point, useful for SQL result sets
+
+    parse_dates : list or dict, default None
+        - List of column names to parse as dates.
+        - Dict of ``{column_name: format string}`` where format string is
+            strftime compatible in case of parsing string times, or is one of
+            (D, s, ns, ms, us) in case of parsing integer timestamps.
+        - Dict of ``{column_name: arg dict}``, where the arg dict
+            corresponds to the keyword arguments of
+            :func:`pandas.to_datetime`. Especially useful with databases
+            without native Datetime support, such as SQLite.
+
+    params : list, tuple or dict, optional, default None
+        List of parameters to pass to execute method.
+
+    chunksize : int, default None
+        If specified, return an iterator where chunksize is the number
+        of rows to include in each chunk.
+
+    **kwargs
+        Further keyword arguments as available in trackintels trackintel.io.read_tours_gpd().
+        Especially useful to rename column names from the SQL table to trackintel conform column names.
+        See second example how to use it in code.
+
+    Returns
+    -------
+    GeoDataFrame (as trackintel tours)
+        A GeoDataFrame containing the tours.
+
+    Examples
+    --------
+    >>> tours = ti.io.read_tours_postgis("SELECT * FROM tours", con)
+    >>> tours = ti.io.read_tours_postgis("SELECT * FROM tours", con, index_col="id", started_at="start_time",
+    ...                                  finished_at="end_time", user_id="USER")
+    """
+    if geom_col is None:
+        tours = pd.read_sql(
+            sql,
+            con,
+            index_col=index_col,
+            coerce_float=coerce_float,
+            params=params,
+            parse_dates=parse_dates,
+            chunksize=chunksize,
+        )
+    else:
+        tours = gpd.GeoDataFrame.from_postgis(
+            sql,
+            con,
+            geom_col=geom_col,
+            crs=crs,
+            index_col=index_col,
+            coerce_float=coerce_float,
+            parse_dates=parse_dates,
+            params=params,
+            chunksize=chunksize,
+        )
+
+    return ti.io.read_tours_gpd(tours, **kwargs)
+
+
+@_handle_con_string
+def write_tours_postgis(
+    tours, name, con, schema=None, if_exists="fail", index=True, index_label=None, chunksize=None, dtype=None
+):
+    write_trips_postgis(
+        tours,
+        name=name,
+        con=con,
+        schema=schema,
+        if_exists=if_exists,
+        index=index,
+        index_label=index_label,
+        chunksize=chunksize,
+        dtype=dtype,
+    )
+
+
 # helper docstring to change __doc__ of all write functions conveniently in one place
 __doc = """Stores {long} to PostGIS. Usually, this is directly called on a {long}
     DataFrame (see example below).
@@ -628,3 +740,4 @@ write_triplegs_postgis.__doc__ = __doc.format(long="triplegs", short="tpls")
 write_staypoints_postgis.__doc__ = __doc.format(long="staypoints", short="sp")
 write_locations_postgis.__doc__ = __doc.format(long="locations", short="locs")
 write_trips_postgis.__doc__ = __doc.format(long="trips", short="trips")
+write_tours_postgis.__doc__ = __doc.format(long="tours", short="tours")
diff --git a/trackintel/model/tours.py b/trackintel/model/tours.py
index bc11abd..f36eabc 100644
--- a/trackintel/model/tours.py
+++ b/trackintel/model/tours.py
@@ -57,6 +57,16 @@ class ToursAccessor(object):
         """
         ti.io.file.write_tours_csv(self._obj, filename, *args, **kwargs)
 
+    def to_postgis(
+        self, name, con, schema=None, if_exists="fail", index=True, index_label=None, chunksize=None, dtype=None
+    ):
+        """
+        Store this collection of tours to PostGIS.
+
+        See :func:`trackintel.io.postgis.write_tours_postgis`.
+        """
+        ti.io.postgis.write_tours_postgis(self._obj, name, con, schema, if_exists, index, index_label, chunksize, dtype)
+
     def plot(self, *args, **kwargs):
         """
         Plot this collection of tours.

diff --git a/tests/io/test_dataset_reader.py b/tests/io/test_dataset_reader.py
index 165fdce..3e9f0f9 100644
--- a/tests/io/test_dataset_reader.py
+++ b/tests/io/test_dataset_reader.py
@@ -35,8 +35,8 @@ def matching_data():
         Tripleg_2 overlaps and extents to the right but is almost not covered by label_0
         Tripleg_3 overlaps label_1 to the right and the left but is almost fully covered by it.
     """
-    one_hour = datetime.timedelta(hours=1)
-    one_min = datetime.timedelta(minutes=1)
+    one_hour = pd.Timedelta("1h")
+    one_min = pd.Timedelta("1min")
     time_1 = pd.Timestamp("1970-01-01", tz="utc")
 
     triplegs = [
@@ -146,14 +146,6 @@ class Test_GetLabels:
         assert len(labels[20]) == 223
         assert all(df.columns.tolist() == ["started_at", "finished_at", "mode"] for df in labels.values())
 
-    def test_defaultdict(self):
-        """Test if non existing entries return a correct empty pd.DataFrame"""
-        geolife_path = os.path.join("tests", "data", "geolife_modes")
-        uids = ["010", "020", "178"]
-        labels = _get_labels(geolife_path, uids)
-        empty_df = pd.DataFrame(columns=["started_at", "finished_at", "mode"])
-        assert_frame_equal(labels[-1], empty_df)
-
 
 class Test_GetDf:
     def test_example_data(self):
@@ -242,8 +234,7 @@ class TestGeolife_add_modes_to_triplegs:
 
     def test_mode_matching_multi_user(self, matching_data):
         tpls, labels_raw = matching_data
-        # we add an empty DataFrame with labels in the end
-        labels = {0: labels_raw, 1: pd.DataFrame(columns=labels_raw.columns)}
+        labels = {0: labels_raw}
         # explicitly change the user_id of the second record
         tpls.loc[1, "user_id"] = 1
 
diff --git a/tests/io/test_from_geopandas.py b/tests/io/test_from_geopandas.py
index c04a724..3dc0edd 100644
--- a/tests/io/test_from_geopandas.py
+++ b/tests/io/test_from_geopandas.py
@@ -91,6 +91,17 @@ class Test_Trackintel_Model:
         pfs = _trackintel_model(pfs, tz_cols=["tracked_at"], tz="UTC")
         assert_geodataframe_equal(pfs, example_positionfixes)
 
+    def test_multiple_timezones_in_col(self, example_positionfixes):
+        """Test if datetimes in column don't have the same timezone get casted to UTC."""
+        example_positionfixes["tracked_at"] = [
+            pd.Timestamp("2021-08-01 16:00:00", tz="Europe/Amsterdam"),
+            pd.Timestamp("2021-08-01 16:00:00", tz="Asia/Muscat"),
+            pd.Timestamp("2021-08-01 16:00:00", tz="Pacific/Niue"),
+        ]
+        pfs = _trackintel_model(example_positionfixes, tz_cols=["tracked_at"])
+        example_positionfixes["tracked_at"] = pd.to_datetime(example_positionfixes["tracked_at"], utc=True)
+        assert_geodataframe_equal(pfs, example_positionfixes)
+
 
 class TestRead_Positionfixes_Gpd:
     """Test `read_positionfixes_gpd()` function."""
@@ -296,6 +307,17 @@ class TestRead_Trips_Gpd:
         example_trips.rename(columns=mapper, inplace=True)
         assert_geodataframe_equal(trips, example_trips)
 
+    def test_multiple_timezones_in_col(self, example_trips):
+        """Test if datetimes in column don't have the same timezone get casted to UTC."""
+        example_trips["started_at"] = [
+            pd.Timestamp("2021-08-01 16:00:00", tz="Europe/Amsterdam"),
+            pd.Timestamp("2021-08-01 16:00:00", tz="Asia/Muscat"),
+            pd.Timestamp("2021-08-01 16:00:00", tz="Pacific/Niue"),
+        ]
+        trips = read_trips_gpd(example_trips)
+        example_trips["started_at"] = pd.to_datetime(example_trips["started_at"], utc=True)
+        assert_geodataframe_equal(example_trips, trips)
+
 
 @pytest.fixture
 def example_tours():
diff --git a/tests/io/test_postgis.py b/tests/io/test_postgis.py
index 6b9f03a..3791d46 100644
--- a/tests/io/test_postgis.py
+++ b/tests/io/test_postgis.py
@@ -160,6 +160,25 @@ def example_trips():
     return trips
 
 
+@pytest.fixture
+def example_tours():
+    """Tours to load into the database."""
+    t1 = pd.Timestamp("1971-01-01 00:00:00", tz="utc")
+    t2 = pd.Timestamp("1971-01-01 05:00:00", tz="utc")
+    t3 = pd.Timestamp("1971-01-02 07:00:00", tz="utc")
+    h = datetime.timedelta(hours=1)
+
+    list_dict = [
+        {"user_id": 0, "started_at": t1, "finished_at": t1 + h},
+        {"user_id": 0, "started_at": t2, "finished_at": t2 + h},
+        {"user_id": 1, "started_at": t3, "finished_at": t3 + h},
+    ]
+    tours = pd.DataFrame(data=list_dict)
+    tours.index.name = "id"
+    assert tours.as_tours
+    return tours
+
+
 def del_table(con, table):
     """Delete table in con."""
     try:
@@ -291,6 +310,28 @@ class TestPositionfixes:
         finally:
             del_table(conn, table)
 
+    def test_daylight_saving_tz(self, example_positionfixes, conn_postgis):
+        """Test if function can handle different tz informations in one column.
+
+        PostgreSQL saves all its datetimes in UTC and then on exports them to the local timezone.
+        That all works fine except when the local timezone changed in the past for example with daylight saving.
+        """
+        pfs = example_positionfixes.copy()
+        conn_string, conn = conn_postgis
+        table = "positionfixes"
+        sql = f"SELECT * FROM {table}"
+        t1 = pd.Timestamp("2021-08-01 16:00:00", tz="utc")  # summer time
+        t2 = pd.Timestamp("2021-08-01 15:00:00", tz="utc")  # summer time
+        t3 = pd.Timestamp("2021-02-01 14:00:00", tz="utc")  # winter time
+        pfs["tracked_at"] = [t1, t2, t3]
+        geom_col = pfs.geometry.name
+        try:
+            pfs.as_positionfixes.to_postgis(table, conn_string)
+            pfs_db = ti.io.read_positionfixes_postgis(sql, conn_string, geom_col, index_col="id")
+            assert_geodataframe_equal(pfs, pfs_db)
+        finally:
+            del_table(conn, table)
+
 
 class TestTriplegs:
     def test_write(self, example_triplegs, conn_postgis):
@@ -582,6 +623,51 @@ class TestTrips:
             del_table(conn, table)
 
 
+class TestTours:
+    """Test of postgis functions for tours."""
+
+    def test_write(self, example_tours, conn_postgis):
+        """Test if write of tours create correct schema in database."""
+        tours = example_tours
+        conn_string, conn = conn_postgis
+        table = "tours"
+        try:
+            tours.as_tours.to_postgis(table, conn_string)
+            columns_db, dtypes = get_table_schema(conn, table)
+            columns = tours.columns.tolist() + [tours.index.name]
+            assert len(columns_db) == len(columns)
+            assert set(columns_db) == set(columns)
+        finally:
+            del_table(conn, table)
+
+    def test_read(self, example_tours, conn_postgis):
+        """Test if tours written to and read back from database are the same."""
+        tours = example_tours
+        conn_string, conn = conn_postgis
+        table = "tours"
+        sql = f"SELECT * FROM {table}"
+
+        try:
+            tours.as_tours.to_postgis(table, conn_string)
+            tours_db = ti.io.read_tours_postgis(sql, conn_string, index_col="id")
+            assert_frame_equal(tours, tours_db)
+        finally:
+            del_table(conn, table)
+
+    def test_no_crs(self, example_tours, conn_postgis):
+        """Test if writing reading to postgis also works correctly without CRS."""
+        tours = example_tours
+        conn_string, conn = conn_postgis
+        table = "tours"
+        sql = f"SELECT * FROM {table}"
+        try:
+            tours.as_tours.to_postgis(table, conn_string)
+            tours_db = ti.io.read_tours_postgis(sql, conn_string, index_col="id")
+            assert_frame_equal(tours, tours_db)
+        finally:
+            del_table(conn, table)
+
+
 class TestGetSrid:
     def test_srid(self, example_positionfixes):
         """Test if `_get_srid` returns the correct srid."""

CLN: Iterate over label keys in `geolife_add_modes_to_triplegs`
In #354 the type of the labels dict changed to defaultdict. Now if we iterate over all users we create a lot of empty dataframes in the defaultdict. Two proposed changes to change that:

1. change type back to dict
2. iterate [here](https://github.com/mie-lab/trackintel/blob/feaf7f37b38c1a5659cd8f6ef6982c3b505110dd/trackintel/io/dataset_reader.py#L226) over labels key instead of unique user_ids
tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_multiple_timezones_in_col tests/io/test_from_geopandas.py::TestRead_Trips_Gpd::test_multiple_timezones_in_col
tests/io/test_dataset_reader.py::TestReadGeolife::test_loop_read tests/io/test_dataset_reader.py::TestReadGeolife::test_print_progress_flag tests/io/test_dataset_reader.py::TestReadGeolife::test_label_reading tests/io/test_dataset_reader.py::TestReadGeolife::test_wrong_folder_name tests/io/test_dataset_reader.py::TestReadGeolife::test_no_user_folders tests/io/test_dataset_reader.py::Test_GetLabels::test_example_data tests/io/test_dataset_reader.py::Test_GetDf::test_example_data tests/io/test_dataset_reader.py::TestGeolife_add_modes_to_triplegs::test_impossible_matching tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_renaming tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_setting_geometry tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_set_crs tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_already_set_geometry tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_error_no_set_geometry tests/io/test_from_geopandas.py::Test_Trackintel_Model::test_tz_cols tests/io/test_from_geopandas.py::TestRead_Positionfixes_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Positionfixes_Gpd::test_mapper tests/io/test_from_geopandas.py::TestRead_Triplegs_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Triplegs_Gpd::test_mapper tests/io/test_from_geopandas.py::TestRead_Staypoints_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Staypoints_Gpd::test_mapper tests/io/test_from_geopandas.py::TestRead_Locations_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Locations_Gpd::test_extent_col tests/io/test_from_geopandas.py::TestRead_Locations_Gpd::test_mapper tests/io/test_from_geopandas.py::TestRead_Trips_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Trips_Gpd::test_with_geometry tests/io/test_from_geopandas.py::TestRead_Trips_Gpd::test_without_geometry tests/io/test_from_geopandas.py::TestRead_Trips_Gpd::test_mapper tests/io/test_from_geopandas.py::TestRead_Tours_Gpd::test_csv tests/io/test_from_geopandas.py::TestRead_Tours_Gpd::test_mapper tests/io/test_postgis.py::TestGetSrid::test_srid