B Line (RTD)

B Line
B Line train at Westminster Station
Overview
Other nameNorthwest Line
OwnerRegional Transportation District
LocaleDenver metropolitan area
Termini
Stations4
Service
TypeCommuter rail
SystemRTD Rail
OperatorDenver Transit Partners
Ridership157,000 (FY2023, annual)
History
OpenedJuly 25, 2016 (2016-07-25)
Technical
Line length6.2 mi (10.0 km)
Track gauge4 ft 8+1⁄2 in (1,435 mm) standard gauge
ElectrificationOverhead line, 25 kV 60 Hz AC
Route map

B Line highlighted in green
extension
to Longmont
(TBD)
Colorado 119 wide.svg
SH 119
Diagonal Hwy
Boulder Junction
Colorado 157 wide.svg
SH 157
Foothills Pkwy
Louisville
Flatiron
Colorado 121 wide.svg
SH 121
Wadsworth Blvd
Broomfield/116th
Downtown Westminster
Colorado 95.svg
SH 95
Sheridan Blvd
Westminster
US 287.svg
US 287
Federal Blvd
Pecos Junction
CRMF
41st & Fox
Union Station
Amtrak

The B Line is a Regional Transportation District (RTD) commuter rail line that serves stations in Denver and Westminster, Colorado. The B Line opened on July 25, 2016, is owned by RTD, and is operated by Denver Transit Partners. During planning and construction, it was also known as the Northwest Line. It is colored green on system maps.

The B Line's southern terminus is at Union Station in downtown Denver, and its northern terminus is at Westminster station in southern Westminster. This segment is only the first 6 miles of a planned 41-mile corridor that would connect Denver, Boulder, and Longmont. Though the entire length of the B Line was provisioned for in the 2004 FasTracks initiative, it is not currently funded and as of 2026, is not expected to be built out until at least 2042.