Attention, Riders - A Word From Two Rail Chiefs - NYTimes.com Re "Don't Bargain With Rail Safety" (editorial, April 30): The Metro-North Railroad and the Long Island Rail Road, both operated by the Metropolitan Transportation Authority, carry more than 570,000 people every day. As presidents of these railroads, we make operating a safe and reliable system for our passengers our absolute priority. Thus, our railroads have invested over $1 billion on a signaling system providing a level of safety greater than that of many rail systems today. We have made great strides in implementing Positive Train Control (P.T.C.), designed to prevent collisions, on our systems. However, factors beyond our control make it extremely challenging for our railroads to meet the 2015 deadline required by law. Installing P.T.C. technology on the nation's busiest and most congested commuter rail systems requires retrofitting 1,200 miles of track and more than 1,000 rail cars, as well as acquiring currently unavailable radio spectrum. P.T.C. cannot simply be bought off the shelf; much of the software and hardware to operate the system in high-traffic environments is not yet fully developed, let alone approved or in production. Nor has P.T.C. technology ever been tested or operated on a commuter railroad as large as our systems. It's critically important that any additional safety technology installed on our railroads be fully tested first and not undermine our existing safety system. The nation's largest commuter railroads, their customers and the region's taxpayers would benefit from an extension of the 2015 deadline to make sure this major P.T.C. investment will work safely and effectively. The writers are the presidents of Metro-North Railroad and the Long Island Rail Road, respectively.