M (SEPTA Metro)

	SEPTA N-5 train #144 of the M as it enters the Gulph Mills station in Upper Merion, Pennsylvania.
Overview
Locale	Delaware and Montgomery Counties, Pennsylvania, U.S.
Termini	Norristown Transit Center; 69th Street Transit Center;
Stations	22
Website	septa.org/schedules/M1
Service
Type	Light metro
System	SEPTA Metro
Services	Local;
Route number	100 (former)
Operator	SEPTA Suburban Division
Rolling stock	26 ASEA Type N-5 cars
Daily ridership	5,108 (2025, weekdays)
History
Opened	1907
Technical
Line length	13.4 mi (21.6 km)
Number of tracks	1–3
Character	Surface (grade separated)
Track gauge	4 ft 8+1⁄2 in (1,435 mm) standard gauge
Electrification	Third rail, 600 V DC
Operating speed	24 mph (39 km/h) (avg.); 55 mph (89 km/h) (top)
Route map
Route map
	to Norristown–Elm Street and Penn Medicine Station
	13.4 mi
	21.6 km
	Liberty Bell Line
	to Allentown
	12.8 mi
	20.6 km
	12.3 mi
	19.8 km
	King of Prussia extension
	proposed
	11.0 mi
	17.7 km
	10.3 mi
	16.6 km
	9.4 mi
	15.1 km
	8.6 mi
	13.8 km
	7.9 mi
	12.7 km
	Strafford Branch
	to Strafford
	7.0 mi
	11.3 km
	6.8 mi
	10.9 km
	6.4 mi
	10.3 km
	5.9 mi
	9.5 km
	5.4 mi
	8.7 km
	4.5 mi
	7.2 km
	3.9 mi
	6.3 km
	3.4 mi
	5.5 km
	3.1 mi
	5 km
	2.5 mi
	4 km
	1.9 mi
	3.1 km
	1.4 mi
	2.3 km
	0.7 mi
	1.1 km
	0 mi
	0 km
	to Orange Street/Media & Chester Pike/Sharon Hill

The M, formerly known as the Norristown High Speed Line (NHSL), is a 13.4-mile (21.6 km) light metro line in the SEPTA Metro network, running between the 69th Street Transit Center in Upper Darby and the Norristown Transit Center in Norristown, Pennsylvania. Service is operated by the Suburban Transit Division of the Southeastern Pennsylvania Transportation Authority. Originally the Philadelphia and Western Railroad line, the line runs entirely on its own right-of-way. In spring 2025, the M had an average weekday ridership of 5,108.

The M is unique in its combination of transportation technologies. Originally chartered as a Class I (steam) railroad, the line is fully grade separated, collects power from a third rail, and has high-level platforms common to rapid transit systems or commuter rail systems such as New York City's Long Island Rail Road and Metro-North Railroad, but has onboard fare collection, mostly single-car operation, and frequent stops more common to light rail systems. Previously, the M was considered to be a light rail line, according to a 2008 SEPTA budget report; however, the line is currently considered an interurban heavy rail line, according to a 2009 SEPTA business plan, and subsequent capital budgets. It has also been categorized by the American Public Transportation Association as "Intermodal High Speed rapid rail transit".

The purple color-coded line was formerly known simply as Route 100, changed to the Norristown High Speed Line in September 2009, and to its current name in 2025.