Question: The West Amesbury Branch Railroad, was a railroad that once led form Newton Junction, New Hampshire to Merrimac, Massachusetts, the Downeaster is a 145 mi regional passenger train service, managed by the Northern New England Passenger Rail Authority (NNEPRA, created by the State of Maine), and operated by which organization?

Context paragraphs:
Rockland Branch: The Rockland Branch is a railroad from Brunswick, Maine to Rockland, Maine.  A charter was granted in 1849 to build a railway from the Portland and Kennebec Railroad on the west side of the Kennebec River to Rockland.  Construction through the rocky headlands of the Atlantic coast proved more expensive than anticipated.  The Knox and Lincoln Railroad commenced service to Rockland in 1871 using a ferry to cross the Kennebec River between Bath and Woolwich.  The Knox and Lincoln was leased by Maine Central Railroad in 1891, and became Maine Central's Rockland Branch in 1901.  Maine Central purchased the Samoset destination hotel in nearby Glen Cove (a part of neighbouring Rockport) in 1912, and offered direct passenger service for summer visitors from the large eastern cities.  Carlton bridge was completed in 1927 to carry the railroad and U.S. Route 1 over the Kennebec River.  Maine Central sold the Samoset hotel in 1941, and the last Maine Central passenger train to Rockland was on 4 April 1959.  The State of Maine purchased the branch in 1987 to prevent abandonment.  The line has subsequently been operated by the Maine Coast Railroad, the Maine Eastern Railroad, and, beginning in 2016, the Central Maine and Quebec Railway.

Z-Train: The Z-Train was the original name of a proposed passenger train service that would operate primarily on Union Pacific Railroad lines between Los Angeles Union Station, Ontario, California, and a new station to be built adjacent to the Las Vegas Strip, with a travel time of five to five-and-a-half hours.  Amtrak last operated passenger train service to Las Vegas in 1997 on the "Desert Wind".  The train would offer an alternative to traveling on congested Interstate 15.

Maine Eastern Railroad: Maine Eastern Railroad (reporting mark MERR) was a railroad that operated in coastal Maine between Brunswick and Rockland on the state-owned Rockland Branch rail line.  Maine Eastern passenger trains connected with the Amtrak "Downeaster" passenger train and Pan Am Railways at Brunswick Maine Street Station.  The state of Maine did not renew the operating contract with MERR, which effectively ended operations at the end of 2015.

Downeaster (train): The Downeaster is a 145 mi regional passenger train service, managed by the Northern New England Passenger Rail Authority (NNEPRA, created by the State of Maine), and operated by Amtrak.  Named for the Down East region of Maine, the train runs from North Station in Boston, Massachusetts, to Brunswick, Maine, with 10 intermediate stops.  The train also operates five daily round trips between Portland and Boston, three of which continue to Brunswick.

Cariboo Prospector: The Cariboo Prospector or "Cariboo Dayliner" or The BC Rail Budd cars was a passenger train service in British Columbia, Canada, which used Budd Rail Diesel Car trains.  It was operated by the Pacific Great Eastern, later known as the British Columbia Railway Company and then BC Rail.  The train ran from BC Rail's North Vancouver railway station, the one located a few blocks from the current North Vancouver railway station used by the "Rocky Mountaineer", and ran to Lillooet railway station.  From there a section was split from the train that would continue down to Prince George BC Rail station located in BC Rail's Prince George yards.  This train service ended along with the other BC Rail passenger services in 2002.  A section serving the line between Lillooet, Seton Portage, and D'Arcy was replaced by the Koaham Shuttle.

West Amesbury Branch Railroad: The West Amesbury Branch Railroad was a railroad that once led form Newton Junction, New Hampshire to Merrimac, Massachusetts.  Although the railroad does not exist, the Amtrak "Downeaster" line now passes through the Newton Junction station, which is now a pizza restaurant, and most of the railroad, is now a gravel walking trail.

Rail replacement bus service: A rail replacement bus service uses buses to replace a passenger train service either on a temporary or permanent basis.  The train service that is replaced may be of any type such as light rail, tram, streetcar, commuter rail, regional rail or heavy rail, intercity passenger service.  The rail service may be replaced if the line is closed due to rail maintenance, a breakdown of a train, a rail accident, strike action, or if the rail service is not economically viable.

Enola Branch: The Enola Branch is a railroad segment of the Port Road Branch and it was a rail line; the Enola Branch railroad segment and the rest of the Port Road Branch is owned and operated by the Norfolk Southern Railway in the U.S. state of Pennsylvania.  The railroad segment runs from Washington Boro northwest to Marysville and it is a former Pennsylvania Railroad rail line.  Its south end is at a former junction with the Atglen and Susquehanna Branch, where the main segment of the Port Road Branch continues southeast.  Its north end is at the Pittsburgh Line.  Along the way, it meets the York Secondary at Wago Junction (near York Haven) and goes under the Lurgan Branch at Lemoyne.  Norfolk Southern labels the Enola Branch as part of the Port Road Branch, officially ending the Enola Branch's existence as a rail line, the main segment of the Port Road Branch runs from Marysville, Pennsylvania south to Perryville, Maryland.  The line goes through the Enola Yard.

Sunshine Special: The Sunshine Special was inaugurated by the St. Louis, Iron Mountain and Southern Railway, (later the Missouri Pacific Railroad), on December 5, 1915, to provide a premium level of passenger train service between St. Louis, Little Rock, and destinations in Texas.  Until being shifted into a secondary role by the "Texas Eagle" diesel powered streamliner in August 1948, the "Sunshine Special" served as the flagship of the Missouri Pacific Railroad's passenger train service.  The last vestige of the "Sunshine Special" name did not disappear from Missouri Pacific timetables until 1962.

Sydney/Melbourne Express: The Sydney/Melbourne Express was an overnight intercapital passenger train service that operated between the Australia's largest two cities, Sydney and Melbourne, between August 1986 and November 1993.  Operated jointly by State Rail Authority and V/Line the name depended on the direction of travel, with the train nicknamed the 'Sex' or 'Mex'.

Supporting paragraphs: West Amesbury Branch Railroad Downeaster (train)
Answer: Amtrak