Railroad Archives Online
- FondoD0036 - George Werkema Collection
- Serie001 - Burlington Northern Railroad Company
- Sottoserie014 - Photographs
- 003 - Railroads--Buildings and Structures
- 005 - Signals and Signs
- Unità documentariaWerkema575 - Burlington Northern station order board signal at Connell, Washington, in 1987.
- Unità documentariaWerkema576 - Burlington Northern station order board signal at Connell, Washington, in 1987.
- Unità documentariaWerkema577 - Burlington Northern semaphore signals at Eltopia, Washington, in 1986.
- Unità documentariaWerkema578 - Burlington Northern semaphore signals at Gibbon, Washington, in 1986.
- Unità documentariaWerkema579 - Burlington Northern semaphore signals at Glade, Washington, in 1986.
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