diff --git a/doc/adb.rst b/doc/adb.rst
index b2e9aca..5a03975 100644
--- a/doc/adb.rst
+++ b/doc/adb.rst
@@ -1,4 +1,39 @@
 Asian Development Bank
 **********************
 
+This module handles the `Asian Transport Outlook (ATO) <https://asiantransportoutlook.com>`_ source maintained by the Asian Development Bank (ADB, initially) and Asian Infrastructure Investment Bank (AIIB, more recently), specifically the `ATO National Database <https://asiantransportoutlook.com/snd/>`_.
+
+In particular, it converts data from the :ref:`ATO native Excel file format <ato-format>`—both the 2022-10-07 and 2024-05-20 formats—to SDMX and extracts metadata.
+
+.. contents::
+   :local:
+   :backlinks: none
+
+.. _ato-format:
+
+ATO National Database format
+============================
+
+The ATO native Excel file format is characterized by the following.
+There is an `ATO National Database User Guide <https://asiantransportoutlook.com/snd/snd-userguide/>`_ that contains some of the information below, but does not describe the file format.
+
+- Data flow IDs like ``TAS-PAT-001(1)``, wherein:
+
+  - ``TAS`` is the ID of a ‘category’ code with a corresponding name like “Transport Activity & Services”.
+    Individual files (‘workbooks’) contain data for flows within one category.
+  - ``PAT`` is the ID of a ‘subcategory’ code with a corresponding name like “Passenger Activity Transit”.
+  - ``001(1)`` is the ID of an ‘indicator’ code with a corresponding name like “Passengers Kilometer Travel - Railways”.
+  - All data flows with the same initial part like ``TAS-PAT-001`` contain data for the same *measure*.
+    The final part ``(1)`` indicates data from alternate sources for the same measure.
+- Files contain a “TOC” sheet and further individual sheets.
+  See :func:`~.adb.read_sheet`, which reads these sheets, for a detailed description of the apparent format.
+- The files are periodically updated.
+- The update schedule is not fixed in advance.
+- Previous versions of the files do not appear to be available.
+- The file metadata contains a "Created by:" field with information like "2022-10-07, 11:41:56, openpyxl".
+  At least two different dates have been observed:
+
+  - 2022-10-07
+  - 2024-05-20.
+
 .. include:: _api/transport_data.adb.rst
diff --git a/doc/whatsnew.rst b/doc/whatsnew.rst
index 7a87431..5e64e72 100644
--- a/doc/whatsnew.rst
+++ b/doc/whatsnew.rst
@@ -5,6 +5,8 @@ Next release
 ============
 
 - Add :doc:`standards` and :doc:`roadmap` documentation pages (:pull:`9`).
+- Adjust :mod:`.adb` for changes in data format in the 2024-05-20 edition of the ATO National Database (:pull:`20`, :issue:`18`).
+  Document the :ref:`current file format <ato-format>` that the code supports.
 
 v24.2.5
 =======
diff --git a/transport_data/adb/__init__.py b/transport_data/adb/__init__.py
index 9efa3e2..ea7c505 100644
--- a/transport_data/adb/__init__.py
+++ b/transport_data/adb/__init__.py
@@ -4,6 +4,7 @@
 from typing import Callable, Tuple
 from urllib.parse import quote
 
+import numpy as np
 import pandas as pd
 import sdmx.model.v21 as m
 
@@ -167,11 +168,24 @@ def read_sheet(
     data_col_mask = list(map(str.isnumeric, df.columns))
 
     # Handle values not parsed by pd.ExcelFile.parse(). Some cells have values like
-    # "12,345.6\t", which are not parsed to float. Strip the trailing whitespace and
-    # thousands separators, then convert.
+    # "12,345.6\t", which are not parsed to float.
+    #
+    # - Strip trailing whitespace.
+    # - Remove thousands separators ("," in 2022-10-17 edition; " " in 2024-05-20
+    #   edition) and whitespace before the decimal separator ("10860 .6", 2024-05-20
+    #   edition).
+    # - Replace "-" (no data) and "long ton" (erroneous) appearing since 2024-05-20
+    #   edition.
+    # - Finally, convert to float.
     dtypes = df.loc[:, data_col_mask].dtypes  # Dtypes of data columns only
     for col, _ in filter(lambda x: x[1] != "float", dtypes.items()):
-        df[col] = df[col].str.strip().str.replace(",", "").astype(float)
+        df[col] = (
+            df[col]
+            .str.strip()
+            .str.replace(r"(\d)[, ]([\d\.])", r"\1\2", regex=True)
+            .replace("^(-|long ton)$", np.nan, regex=True)
+            .astype(float)
+        )
 
     # Identify remarks columns: any entries at the *end* of `df.columns` with non-
     # numeric labels. Use the index of last data column, counting backwards.