The Federal Railroad Administration (FRA) published a notice of availability on May 5, 2026, regarding a request from the Massachusetts Bay Transportation Authority (MBTA), as host railroad, to permit CSX Transportation, Inc. (CSX) to conduct field testing of the Interoperable Train Control positive train control (PTC) system on two segments of MBTA's North Side Fitchburg and Haverhill Lines using CSX locomotives and equipment. FRA invites public comment on the request through June 4, 2026. This document is a Federal Register notice and not a NEPA environmental review document. No environmental impact analysis, alternatives analysis, or mitigation measures are presented.1234