diff --git a/src/main/resources/siri-2.1/xsd/siri_model/siri_reference.xsd b/src/main/resources/siri-2.1/xsd/siri_model/siri_reference.xsd
index d74be41..8377858 100644
--- a/src/main/resources/siri-2.1/xsd/siri_model/siri_reference.xsd
+++ b/src/main/resources/siri-2.1/xsd/siri_model/siri_reference.xsd
@@ -348,6 +348,11 @@ Rail transport, Roads and road transport
    <xsd:enumeration value="ferry"/>
    <xsd:enumeration value="metro"/>
    <xsd:enumeration value="rail"/>
+   <xsd:enumeration value="taxi">
+    <xsd:annotation>
+     <xsd:documentation>To be used to indicate that a scheduled service is operated by taxi. Should not be used to indicate a regular taxi-service.</xsd:documentation>
+    </xsd:annotation>
+   </xsd:enumeration>
    <xsd:enumeration value="tram"/>
    <xsd:enumeration value="underground"/>
   </xsd:restriction>