S-Bahn logo. From wiki.

This week, Greater Greater Washington has run a series of posts on the hurdles to implementing through-routed commuter rail services in DC. The technical reasons include many basic incompatibilities between the region’s two commuter railroads (MARC and VRE), ranging from type of locomotion to platform height, as well as the infrastructural shortcomings of DC’s rail infrastructure to handle high frequency transit-like operations.

Lost in the wash, however, is the reason to do this.  The reasons are two-fold: First, through-routed service expands the transit network relatively inexpensively, offering mobility benefits to current and future riders.  Second, such a service (and the technical changes required to implement it) help solve some of the other challenges of DC’s commuter rail network (such as insufficient storage capacity at Union Station for trains to layover mid-day). Through-running is both a means to an end as well as an end itself.

This isn’t exactly a new concept, as it has been raised in numerous places over the years:

• MARC Growth and Investment Plan
• VRE Strategic Plan
• Greater Washington Board of Trade Study (from a GGW commenter)

Plus the southern intentions of intercity rail:

• Amtrak’s HSR vision and the SE HSR corridor
• Amtrak’s NEC master plan
• Virginia’s desire for expanded rail service

CSX’s plans for increasing freight traffic will also mean added capacity through DC, with implications for passenger rail.

None of these plans hints at even the possibility of the kind of S-Bahn integration potential that through-routing unlocks.

The goal should be to turn the core of DC’s commuter rail network into a system like Germany’s S-Bahns (touched on previously here and here).  David Alpert essentially suggested the same thing with his conception of the ‘Metro Express.’  The level of service would be more like rapid transit than commuter rail.  The geographic extent might not be as expansive as the current commuter rail network (there’s no sense in running rapid transit to Martinsburg, WV) but those outer extensions could easily be serviced by a service that mirrors today’s commuter rail.  The core of the network (say, to Woodbridge in the south, Manassas in the west, Germantown or even Frederick to the north, and Baltimore to the east) would see higher frequencies, through-routed service, and all-day, full week service.

One common characteristic of S-Bahns is the use of interlining and shared tracks in the core of the system (this Wiki diagram illustrates), where interlining produces short headways on the shared portion while the outer parts receive less frequent service due to the branching of the network. The three MARC lines feeding DC, each running on 30 minute headways would combine for 6 tph in the shared segment (Union Station to Alexandria).

VRE’s timetable shows Alexandria-L’Enfant at about 17 minuntes; Alexandria-Union Station at about 25 minutes.   There’s room for massive improvement here – Metro’s trip planner shows King Street to Union Station (Yellow to Red) as 20 minutes on Yellow, 4 minutes on Red; King Street to L’Enfant Plaza is the same 17 minutes on the Yellow line.

Give a DC S-Bahn transit-like service and that can be reduced.  Electric multiple unit trains would accelerate faster; level boarding and more frequent service would shorten station dwells; etc. Then, the commuter rail infrastructure would function as a key part of the region’s rapid transit network.