Heavy Rail: In general, Heavy Rail denotes a railway line engineered to handle conventional full-weight, higher speed passenger cars, and all types of freight equipment. The term also applies to the more expensively built dedicated passenger rail systems like the New York City Subway. All Vermont rail routes are heavy rail lines, but some light rail vehicles might be allowed to operate on these rails.

Light Rail: In general, Light Rail denotes a rail system with more "lightly constructed" infrastructure and passenger cars, compared to heavy rail routes. Initially this term was used for new electric streetcar lines, but it has evolved to cover intercity electric and diesel powered trains as well. In multiple cities, light rail passenger trains share track with heavy rail freight service, although not always at the same hours. When light rail cars do operate simultaneously with freight trains, they must meet heavy rail crash standards.

Hybrid Rail: Term used for examples of mixed-use “hybrid” heavy/light rail lines. Boston’s “Green Line” Riverside branch was originally a Boston and Albany heavy rail commuter line. It was converted for the exclusive use of MBTA light rail electric cars. Several new DMU light rail lines, like New Jersey’s River Line, host freight trains late at night, when no passenger trains are in service. The new DMU routes profiled above use light rail DMU equipment which can mix at the same hours with freight trains. RDCs are heavy rail cars, yet are suitable for use on services that might be considered a hybrid of heavy and light rail, as in Portland, Oregon (see below).

Commuter Rail: Train service operated from suburban towns into a central city, always at rush hours, but often throughout the day and evening. A commuter service can use either heavy or light rail equipment. The “classic” commuter rail services are those in the major metropolitan areas like the MBTA heavy rail network around Boston, feeding riders into North and South Stations, but more recently networks have opened using heavy rail equipment serving the smaller markets of Orlando, Florida; Santa Fe, New Mexico; and the Salt Lake Valley in Utah.

Regional Rail: Regional Rail services have some of the characteristics of commuter rail, but typically serve more than just one city destination. The amazing Swiss train/tram/bus networks around relatively small centers like Chur, (population under 40,000), and St. Gallen are good examples. Heavy and light rail trains are tightly integrated with local bus and tram services, offering both commuter and longer distance service. Despite not having a single city with a population of a million residents, the Swiss network offers at a minimum hourly service all-day on all train lines. In the Portland, Oregon area over 60 miles of light rail electric services are running, plus a shorter 15 mile-long DMU/RDC heavy rail route. Denver, Colorado is in the process of completing over 100 miles of fully-integrated electric-powered heavy and light rail lines, extending out nearly 30 miles from the city center. If a more intensely served passenger rail system was developed in Vermont it would best be called Regional Rail.

Streetcar/tram: Historically called the trolley car, these terms denote in-street city rail service. Typically, such lines are built to a lighter track and car-body standard. Electric power from overhead catenary is almost always used. In many cases (especially in Europe) a narrowed track gauge is selected, to reduce the line’s in-street footprint. Streetcar lines can also run in private rights of way and even in subways (as with the downtown “Green Line” in Boston), but in-street operation is the most common setting. Streetcars have higher capacity than busses and typically cost much less to operate than diesel-powered equipment, but there is a higher initial construction cost for the overhead electrification.

MU (Multiple Unit) Equipment: Most light-rail systems use permanently-coupled, multiple car train-sets, either electric (EMU) or diesel (DMU) powered. In some cases these cars may operate using both in-street tracks (as with a streetcar), as well as track built on dedicated private rights of way. Self-propelled MU cars need no added locomotive. MU cars can be built for either heavy or light rail service.

DMU: Diesel Multiple Unit railcar, for heavy or light rail use. A Budd RDC car is a type of DMU. 

RDC Car: A type of DMU designed and built in the USA by the Budd Company from 1949-1962, still in use in North America.

FRA Track and Speed Classification Standards: This is the system used for speed authorization on US rail lines. With track infrastructure lacking line-side block signals, but with well-maintained roadbed and rails, a line meets the Federal Railroad Administration (FRA) Class Three Track standard, and passenger trains can run at speeds up to 59mph. Most Vermont routes are Class Three Track. Many US lines meet a higher FRA Class Four standard, for tracks protected by line-side signals. This allows passenger operation at up to 79mph. With block signals that also display inside the drivers’ cab, passenger train speeds up to 89mph are allowed. A few Amtrak lines have the added protection of automatic train stop if the train passes through a red/stop signal. This is FRA Class Five Track and permits trains to run up to 110mph. On Amtrak’s Northeast Corridor, where all at grade street crossings have been eliminated, speeds are allowed up to 125mph for conventional equipment and as fast as 150mph (in a few areas) for ACELA EXPRESS trains. All Class Five track must be Positive Train Control (PTC) protected by 2018 (see below).

PTC (Positive Train Control): PTC is a satellite-based, in-cab computer speed control and train-stop system being installed on high volume signal-protected rail lines. No Vermont rail routes, because of moderate traffic volumes, currently require the installation of this costly technology. Most Vermont tracks are FRA Class Three 59mph un-signaled lines. The one section of 79mph Class Four Vermont trackage on the New England Central RR is also currently PTC exempt.