Hardy, long-lasting, and fast growth...that's a pretty tall order!
Eastern hemlock would not be my first (or second) choice for establishing a noise buffer...growth is too slow. Emerald Arborvitae would work, as would white pine or white fir. I suggest planting them 10-feet apart.
A double row is also suggested, if you have the real estate to accommodate the extra shrubs. You may want to think about dogwoods, hazelnut, wild plum, or viburnums. I suggest planting them 4-6 feet apart.