This is not the time to consider cutting back on the increasingly successful Amtrak Keystone route between New York and Harrisburg by way of Philadelphia. But that service could be curtailed if negotiators for Amtrak and the state Department of Transportation can't agree on a way to cover costs.

Amtrak must end its $8 million contribution on Oct. 1, 2013, under a 2008 law requiring Amtrak to shift operating costs to the states. The train operator would continue to cover infrastructure maintenance.

Pennsylvania has had time to plan for the subsidy shift, but with a tight budget and Gov. Corbett's refusal to raise taxes, service could be cut back. Pennsylvania already spends $9 million a year to underwrite the Keystone line's operations.

Dropping the line would be a shame, considering that efficient rail service makes Pennsylvania more attractive to businesses. Sending thousands of riders to Pennsylvania's neglected highways would be a problem for everyone. It would add to traffic, worsen the wear and tear on crumbling roads, and increase air pollution.

Recent investments by Amtrak, the state, and the federal government have resulted in improved service and ridership. Improvements include a $145 million upgrade to the 104-mile corridor, and a $40 million makeover for a rail intersection near Harrisburg.

Next year, Amtrak is scheduled to put new locomotives on the Keystone line, whose trains can travel up to 125 miles per hour, making it among the fastest lines in the Northeast Corridor.

With the rail improvements, ridership on the line, which offers 14 round trips daily, has doubled to 1.3 million since 2000. Riders' fares cover 73 percent of the line's costs. In the first nine months of 2012, ticket revenue was $27.5 million, while costs were $37.8 million. Revenue for that period was up 11 percent from a year ago.

The Keystone line is clearly moving in the right direction. The potential for future growth adds urgency to the need to settle how to handle the subsidy shift so service cuts can be taken off the table.