A senior Railway Board official was arrested by the CBI Wednesday for allegedly receiving a bribe from a Mumbai-based tour operator in return for facilitating to run special trains and additional coaches for tourist purposes.Ravi Mohan Sharma, a 1997 batch official of Indian Railway Traffic Service (IRTS), was caught by a team of the Central Bureau of Investigation (CBI) while accepting the bribe of Rs.5 lakh at his Delhi residence."The money was being paid through Hawala channel. The alleged bribe was being given to facilitate the running of special trains and additional coaches for tourist purposes," said a CBI official.