The train leaves at 6.05am and arrives in Batticaloa at 2.45pm. The express bus to Pottuvil which takes another 3 or 4 hours comes directly to the railway station and waits for the train to arrive before leaving. A tuk tuk from Pottuvil to Arugam Bay will be about 200-300LKR.
There is also a night train leaving at 7pm and arriving at 3.55am. Sleeper berths and reclining seats are available on this service. See Seat61.com (opens in a new window) for more details.
The advantages of this service over the hill train are a faster overall journey time and normally a less crowded experience with less tourists.
The disadvantages are that the train runs at lower altitude and there is no ac option so it can be hot at times, especially when the train stops for more than a few minutes at a station. The views are also nowhere near as spectacular but impressive nonetheless.
See Reserve a Train Seat in Advance for more information.