I would define each mode based on capacity, vehicles and operating environment, and stop spacing. Power collection can be added if need be. I am limiting the definitions to North American usage. I personally do not understand the fuss over definition. Most transit experts will tell you the definitions have been blurred over the decades, and people have their own.Here is what I normally use:
REGIONAL RAIL: High Speed, High Capacity Transit with stops 2km or greater outside a city centre, and between 800M to 1000m in the city centre. Can utilize own ROW, or existing freight lines. Trains can be Diesel or electric loco-hauled trains, or multiple units. Can also be called Commuter Rail, or S-Bahn.
SUBWAY: North American term to describe high speed, high capacity rail transit in fully grade-separated ROW, mostly in tunnel with some elevated, or open cut sections. Trains are always electric powered, and can run either as single vehicles or mutliple units. Can be called a Metro, or U-Bahn. Speed is high. Stop spacing varies between 500m to 1600m
LIGHT RAIL TRANSIT - Medium to High Capacity rail transit that utilizes its own ROW. The ROW can vary from a reserved surface ROW with signal priority to fully grade-separated elevated or tunnel ROW. Vehicles can be electric, or diesel powered and run as a single vehicle or coupled into a train. Speed can vary depending on operating environment. Stop spacing varies between 500m to 1000m
STREETCAR - Low to medium capacity rail transit that usually runs in mixed transit with no signal priority, but is able to run in surface ROW. Vehicles are always electric powered, single vehicles. Can be coupled together if necessary. Speed can vary depending on environment. Stop spacing can vary between 300m to 600m. In Philidelphia, Streetcars are called TROLLEYS.
BUS RAPID TRANSIT - Medium to High Capacity bus transit that utilizes it's own ROW. The ROW can vary from a reserved ROW to fully grade separated elevated or tunneled sections. Vehicles can be electric or diesel powered, and will always run as single vehicles. Vehicles tend to be higher quality buses with amenities. Speed varies depending on operating environment. Stop spacing varies between 500m to 1000m.
HIGHER ORDER BUS - Low capacity bus transit that runs in mixed traffic, and may utilize queue jumps lanes and signal priority at stops, and some reserved bus lanes. Buses are normally branded to distinguish from local bus routes. Can also be called limited stop routes.
Stop spacing varies between 500m to 1000m
LOCAL BUS - Low capacity transit that runs in mixed traffic with no signal priority. Stop spacing is usually 250m to 500m.
Agree with all, except the stop spacing. Really, who would care about the station distance between one to another? While most stop spacings as you mentioned are norm, there is really no official definition of how long each mode of transit must travel before it makes a stop. The GRT I-Express "BRT" is really has longer stop spacings than 1km.
For HRT/LRT, a real rapid transit is to have minimal traffic contact, regardless of capacity or environment. What to me a "Shep E. LRT" is, really nothing more than a "highly polished halo" in an attempt to masquerade streetcar as a "rapid transit". Or Spadina streetcar. Queensway streetcar would have been a true LRT, if there was fewer contact with street traffic and complete ROW throughout its leg from Lake Shore and underground through Queen. The transition from street surface at Eglinton West, underground in midtown and street surface again beyond Don Mills really kills the rule of LRT.
One extra correction: Higher order bus could mean in any capacity (from low to high capacity). Route 110 [University-Clarkson-403] in MT is an high-order express bus using a mix of regular size and articulated fleets.
As for rest of the terminology you defined, I concur, but I'll pretend that I didn't see stop spacing.
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So I'll update my glossary.
Commuter rail: A heavy-capacity rail transit on existing railways. Must be complete ROW, or use freight lines. Has transit signal priority. Trains can be DMU, EMU or mixed multiple unit.
Metro (Subway): A heavy-capacity rail transit, on any rail-specific railways. Can be light or heavy rail, but must have its own traffic right with minimal or no contact of street traffic. Called subway in T.O; in Montreal, it's called Metro.
Streetcar: A light-capacity rail transit, intended to serve as an alternative of bus preferably by means of electrification on light rails (though diesels may apply). Can be applied to rails on street median, dedicated lanes or on any part of the street. Can count grade-separate lines or in non-street surface. But must obey street traffic.
LRT: Light Rail Transit. Rapid rail service with limited stops by means of light rail vehicles. Must be partial or complete ROW, with minimal contact with street traffic.
HRT: Heavy Rail Transit. Rapid rail service with limited stops by means of heavy rail vehicles. Must be partial or complete ROW, with minimal contact with street traffic.
LRV: Light rail vehicle.
HRV: Heavy rail vehicle.
BRT: Bus rapid transit. Rapid bus service with limited stops by means of buses specially designed for express routes on bus-exclusive lanes. Must be partial or complete ROW, with minimal contact with street traffic.
Express bus: Limited-stop bus routes, with little distinguishes on travelling by means of ROW or grade-separate roadways.
Bus: Just another bus you see in your area.