April 17 (Reuters) - U.S. railroad operator CSX reported first-quarter earnings above Wall Street estimates on Wednesday, helped by higher intermodal volumes and coal export demand, sending its shares up 2% in after-hours trading.

The Jacksonville, Florida-based company's net earnings fell to $893 million, or 46 cents per share, for the quarter ended March 31, from $987 million, or 48 cents per share, a year earlier.

However, it narrowly beat profit estimates of 45 cents per share, according to LSEG data.

Revenue slipped 1% to $3.68 billion, but it was slightly above analysts' average expectations of $3.67 billion.

The year-on-year fall was due to lower fuel surcharge, weaker trucking revenue and reduced export coal prices, which offset gains in merchandise pricing and higher intermodal and coal volumes.

The company reported quarterly merchandise volumes of 645,000 units, marginally down from 647,000 units a year ago. Its total coal shipments were up 2% at 21.2 million tons, while domestic shipments were down 17% on the back of replenished utility stockpiles and weaker natural gas prices.

Unfavorable winter weather and the recent collapse of Francis Scott key bridge in Baltimore posed infrastructure and operational challenges to railroads, which continue to operate in an elongated freight downcycle.

Earlier this month, CSX said it was starting a new freight rail service between Baltimore and New York in order to circumvent the closure of the Port of Baltimore following the bridge collapse.

It also said its existing coal customers should expect "potential shipment delays" after the accident and added that it plans to keep its Curtis Bay coal pier operational, which is located near the site of the accident.

The company's operating margin came in at 36.8% for the quarter, down 2.7% from a year earlier.

CSX's East Coast competitor Norfolk Southern is scheduled to report its first-quarter results on April 24. (Reporting by Abhinav Parmar and Aatreyee Dasgupta in Bengaluru; Editing by Maju Samuel)