In General
Thomas Viaduct
St Denis Station
St Thomas Viaduct Monument
B&O Mileposts
Elkridge Station
the Relay House Hotel


In General

Location / Name:
Relay MD, Baltimore County
Elkridge MD, Howard County

What's Here:
Thomas Viaduct
St Denis MARC Station
Thomas Viaduct Monument
CSX over Route 1
B&O Mileposts (for ref)
Elkridge Station (for ref)
Relay Hotel (for ref)

GPS Coordinates: as needed
Phone A/C: 410/443c
ZIP: 21227 Relay side, 21075 Elkridge side

Access by train/transit:


The Scoop:

Probably the most notable structure on the map is the famous Thomas Viaduct - it is in Elkridge/Relay.  It is the oldest curved stone arch bridge in the U.S. still in operation.  Good pictures can be had from both ends, so you don't have to worry at what time of the day you get there, altho CSX hasn't done as good a job at keeping the growth down as the B&O did.  The bridge spans the Patapsco River, the xx Park, and the county line, so the east end is in Baltimore County, while the western end is in Howard County.

A monument to the Viaduct sits along the main line, in the middle of the split.  The only way I know of to get there without crossing the tracks, is by climbing the embankment coming up from the park road below.  The only picture I have seen of it from the Library of Congress has so much horrible graffiti on it, including Nazi stuff, that I am not going to post it here.

There used to be a pair of really nice vintage mileposts located by the Old Main Line split from who knows how long ago,  They unfortunately disappeared around the  2007/2008 timeframe, removed by whom, no one seems to know - an unfortunate loss for us all, for they were very unique!

You also have the B&O Old Main Line, the first railroad line in the U.S. going to Ellicott Mills (now Ellicott City).  It splits off from the main line in Relay, the eastern side of the viaduct.  The Old Main Line offers a lot of good photo ops, just refer to a good map of the area, and bring along a fair amount of patience, but your rewards will be great!  One of my favorite spots is the bridge and tunnel in Ilchester, best for westbound freights, so you can catch 'em coming out of the tunnel.

St Denis: Things have changed at St Denis since I first did this guide.  Railfanning is no longer allowed outside the rush hours.  Well, it's not so much tghat railfanning is not allowed, it's just in general, people are not allowed on the platforms during :non-business" hours.  I have not heard a reason for instituting the no trespassing restriction.  With that said, mornings can be a good time at St Denis, I caught 5 trains in about an hour there around 8am, three MARC commuters, and two freights for the Old Main Line.  I don't know if the restriction carries onto -just being parked at the parking lots- or not, maybe someone can let me know?

CPL signals: Sorry, but CSX replaced them in the 2010 timeframe, darnit......

Halethorpe is a good spot for Corridor pictures, and is just up the road via Route 1.

Three items of interest on this page are for historical reference only, as they are long gone:
-- 1) A pair of vintage B&O Mileposts
-- 2) The Relay House Hotel
-- 3) The Elkridge Station

Early on, the B&O had a station on the Elkridge side of the viaduct.  MARC also used the site for a while.  Not much remains.

Also, parking on Lawyers Hill Rd at the western, or "southern" end of the Thomas Viaduct is no longer possible, as the county did away with the convenient spot for parking there years ago :-(

Note: even though the B&O's tracks go north and south, the B&O referred to the directions as East (north) and West (south).  I use the north and south terms mostly, only because it is easier to reference to the maps.

A lot of the pictures I use are taken on signal hunting trips with Michael Watnoski, as we scoured the area for those elusive CPL's and PL's (seems like a lifetime ago :-).

As far as food and other services go......  A few of my favorite restaurants in this quadrant are the Double-T off exit 16, and G&M's and Snyders off exit 8 - they all have lines getting into them during the popular hours, attesting to the quality of their food (especially G&M's if you want some of the best Crab Cakes in Baltimore).

Interstate 895 sucks for commuting around, since it is not one of those roads you CAN'T get on n (mostly) off as easily like you can with the rest of the interstates around Baltimore.  This stems from the fact that it was a toll road in the beginning, and for some reason, Maryland has been happy to keep it as a very limited access highway.

Mike Brotzman
Denver Todd
Google Maps
Bing Maps
Open Railway Map

Websites and other additional information sources of interest for the area: history and importance of Relay


The above map is available in PDF format here

This map is available here
as a PDF


  Thomas Viaduct

GPS Coordinates: 39.22195, -76.71316 (center)

I'm sure when the Thomas Viaduct was first built, the designers held their breath as a small engine of the time went over it for the first time.... if they could just be around today to see 6000HP behemoth's go over it now!

Thomas Viaduct was the first stone masonry arch bridge on a curve built in the United States.  Construction started July 4th, 1833, and was completed on July 4th, 1835.  The bridge was named for Philip E. Thomas, first president of the B&O RR.

The bridge is 612 feet long, the average arch span is 58 feet (of which there are eight of them), the average height of the arches is 59 feet, the width of the bridge is 26'-4".  It cost $142,236 in 1830's money, which today, would equate to roughly $2.7 million.

The viaduct crosses the Patapsco River and the Patapsco Valley State Park, and is about a half mile south of the St Denis station.

St Denis MARC Station

GPS Coordinates: 39.22422, -76.70397

The St. Denis station dates back to the old B&O days.  The current "station" (if you can call it that), was put in place when MARC started it's commuter service back in the MDOT days.  When I first went to college in 1969, I would come over here to "study" and watch trains - there was a real depot here then (well - kinda, sorta :-).  The B&W picture below is the only one I have come across of it, and it was taken by my best friend John's father, Leonard Buxton - one of the greatest railfans of all time!!!

From Mike Brotzman comes this: ST DENIS interlocking was constructed in 2006 as a replacement for the older HALETHOPRE interlocking (at HX Tower) about a mile to the east.  This lengthened the storage area for inbound trains to the southern Baltimore Terminal yard complex that branches off at WEST BALTIMORE interlocking. St Denis was at the junction of the CSX Capitol Sub, Baltimore Terminal Sub and Old Main Line Sub.

  St Thomas Viaduct Monument

GPS Coordinates: 39.22252, -76.71292

I'm not sure how you get to this without trespassing, because it is in the middle of the Main Line and Old Main Line split. The climb up the embankment from River Road is a tough one, especially when everything is in full bloom.

  Vintage B&O Mileposts

GPS Coordinates: 39.22195, -76.71316 (center)

Elkridge Station

GPS Coordinates: 39.21528, -76.71068

The B&O RR had a station here, not sure of the dates for the structure.  MARC at one point, used this location in lieu of St Denis for a while.  As you can see in the historic picture, there used to be a grade crossing here - not sure when they closed that off.  Then, an underpass was built so commuters did not have to cross the tracks.  The underpass is still there, but it is closed off rather well, and if you go there, I would not advise trying to break in, as CSX police check on a regular basis when they are out this way.  I believe there are signs that say no trespassing, so if you go there to catch a freight or MARC train, scamper away quickly, the engineers will call you in.

  Relay House Hotel

GPS Coordinates: 39.22285, -76.71290

From Wikipedia: Relay House on the Patapsco River, was also known as the Viaduct Hotel.  Constructed in 1872 at a cost of $50,078.41, the hotel was closed in 1938 and eventually demolished in 1950.  The hotel would have been where the yellow "X" is.

in 1910 / Via Wikipedia

Bridges and Tunnels

Thomas Viaduct

Covered above as sight #1.

CSX over Route 1

GPS Coordinates: 39.21598, -76.71117


EB Color Light Interlocking Signals at St Denis

GPS Coordinates: 39.22470, -76.70267

The signals here at St Denis are a "brand new" set of signals.  They replace CPL signals which used to be at the interlocking in front of HX tower, about a mile north of here.  The interlocking HX Tower used to control, has now been moved to "just before" the St Denis station.  The two pictures at the bottom show the area in front of HX now, and where the two locations are related to each other.  You can also see the nice straight tracks in front of HX in the one shot.

A few shots way before the signals were put into service (2005)

WB Color Light Interlocking Signals near St Denis Station

GPS Coordinates: 39.22690, -76.69500

This picture was taken from where HX Tower stands, and the signals are almost a mile distant.

2008, Mike Brotzman

Color Light Interlocking Signals at Gun Rd

GPS Coordinates: 39.22889, -76.72186

In this quiet little corner of the Patapsco State Park, you have a closed grade crossing on the Old Main Line, a set of interlocking signals, track lubricator, an old concrete telephone booth, a switch machine, and of course, grade crossing lights which no longer see any vehicular traffic.  The signals are made by Safetran.

At the grade crossing are the tracks coming from St Denis, and it is a single track. West of here it is double track for about 1.9 miles to a point in the park near " Grist Mill/Saw Mill Branch/Buzzard Rock/Forest Glen Trails", approx GPS Coordinates: 39.24312, -76.75027.


None for now.....


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2009-0511, 2009-0503, 2005-0828, 2005-0809, 2010-0625

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Last Updated: 05/06/2024