The Society of Indian Automobile Manufacturers, SIAM on Wednesday said the size of the domestic passenger vehicles market is likely to touch 5.6 million units by 2017.Stating this, SIAM President Pawan Goenka also said, at the industry body's annual summit in New Delhi, that exports may touch 1.3 million units by the end of 2017. But he also observed that due to the slowdown in recent months, the industry may have to further revise downwards the growth projection for passenger vehicles and commercial vehicles.In July, SIAM had projected 11 to 13 per cent growth in vehicle sales in the country, down from 12 to 15 per cent growth it had forecast in April.