Complex sentence: The authorities also expect to generate AED 18 billion/US $4.9 billion in income over the next 10 years; but they speculate that the Metro would not be a profit-making enterprise, since the fares would be subsidised.
Split into simpler sentences: The authorities also expect to generate AED 18 billion/US $4.9 billion in income over the next 10 years. But they speculate that the Metro would not be a profit-making enterprise since the fares would be subsidised.