Sentence:  Two sets of Mk. 2 coaches hauled by Class 37s were introduced on peak Rhymney services during the summer. The coaches do not comply with the Persons with Reduced Mobility (PRM) standards and would therefore need a <WSD>derogation</WSD> to continue in passenger service after 31 December. 
Meaning of the word marked with <WSD> tags:  The act of derogating; the temporary or partial nullification of a law.