Tuesday, May 5, 2015


I'm a follower of Ben Brown's blog chronicling the construction of his Maine Central layout and his posting regarding the compromises to fit the prototype into a physically constrained space inspired me to look closer at solving the problem I have with designing the south end of the Fairgrounds Branch where the elevation changes are a signature element of the scene.

In Proto:48 (O scale), grades and vertical dimensions require even more space to accomplish and I'd like to avoid un-prototypical compromises like 5% grades in the process of recreating the Fairgrounds Branch.

First, a review of the prototype:
The red lines are the rails

The blue line running east to west represents a vertical rise to the east in 170 feet

The orange line running north to south represents a vertical rise to the south in approximately 766 feet

The purple line running north to south represents a vertical rise to the north in approximately 867 feet

Using a topographic map available on HistoricAerials.com, I was able to approximately measure elevations at the following points:

Safeway Bakery:815ft
34th St Lower:825ft
34th St Upper:852ft
Wolferman driveway:840ft
Karnes Blvd:852ft

That translates into the blue line equaling approximately a 25ft rise, the orange line an approximately 15ft rise, and the purple line an approximately 10ft rise.

Thanks to some dedicated area Frisco modelers, I obtained a set of GPS data points, but it contains some fairly wide variations and I don't know the accuracy of any of the devices.  Arithmetic means should help smooth that out and the addition of the data points read from the topo map paint a reasonable picture. 
LocationGPS MeanGPS #1GPS #2GPS #3GPS #4TopoMean w/ Topo
34th St Lower840.00843846841830825837.00
34th St Upper858.25873859861840852857.00
Wolferman's 852.25846856851856840849.80

Using the mean values including the points from the topographic map results in the following grades:
34th St Lower to 34th St Upper (blue)2017011.76Seems OK for a road...
34th St Lower to Wolferman's (orange)137661.69Steep enough to roll away...
Wolferman's to 34th St Upper (purple)138671.49...better set more handbrakes!
Except that 13ft rises on each rail leg doesn't align with only a 20ft rise on the road leg, so that one is actually 15.29% when a 26ft rise is used.

There's another spur serving Southwestern Bell Telephone and U.S. Engineering (not shown on map above) that I'll probably just keep even with the lower 34th St crossing elevation.  There will still be plenty of visual contrast and operational challenge as the "main line" of the branch rises behind it to climb to Wolferman's.

With at least the relative difference between these elevations reasonably figured I can continue with the track planning process.  It remains to be seen how much I will have to steepen these grades to compress the model length-wise into available space.   Stay tuned...