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 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.
| Location | GPS Mean | GPS #1 | GPS #2 | GPS #3 | GPS #4 | Topo | Mean w/ Topo |
|---|---|---|---|---|---|---|---|
| 34th St Lower | 840.00 | 843 | 846 | 841 | 830 | 825 | 837.00 |
| 34th St Upper | 858.25 | 873 | 859 | 861 | 840 | 852 | 857.00 |
| Wolferman's | 852.25 | 846 | 856 | 851 | 856 | 840 | 849.80 |
Using the mean values including the points from the topographic map results in the following grades:
| Segment | Rise | Run | Grade | Notes |
|---|---|---|---|---|
| 34th St Lower to 34th St Upper (blue) | 20 | 170 | 11.76 | Seems OK for a road... |
| 34th St Lower to Wolferman's (orange) | 13 | 766 | 1.69 | Steep enough to roll away... |
| Wolferman's to 34th St Upper (purple) | 13 | 867 | 1.49 | ...better set more handbrakes! |
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...
