Sunday, April 29, 2007

Summit Tunnel

From: "Edward L Hodges"

I was hiking over Donner Pass yesterday and came across the bronze plaque commemorating the Summit Tunnel project. I looked around in all directions and wondered why the engineers decided to tunnel through so much rock when there appeared to be an alternative. The alternative, to me, seemed to be to add a few extra loops to the route to gain the needed elevation to cross the summit without the need for a tunnel. Would you direct me to the appropriate link which explains why the engineers chose to spend so much time, money, and material to save 125 feet in elevation?

—Ed Hodges, San Jose


Blogger CPRR Discussion Group said...


I can't speak for certain, but it might be that the vertical cliff face on the east side of the tunnel (and perhaps a shelf or break in the face at the level of the tunnel) led them to the tunnel instead of the increased elevation.


4/29/2007 4:34 PM  
Blogger CPRR Discussion Group said...

From: "Edson T. Strobridge"

The question of saving 125 feet of elevation was important. The Central Pacific tried to hold their grade to a 2% maximum grade, about 116 feet to the mile) preferably even a lesser grade if at all possible. To go over the top of Donner Pass at that location, if the elevation was 125 higher would have required about 2 1/2 miles of additional track to maintain the maximum grade allowed just to cover the 1689 feet of the length of the summit tunnel. The east portal of that Tunnel #6 was about 33 feet lower than the west portal; that elevation which would have increased the 125 additional feet of elevation by about that amount which would have added up to about 158 feet which would have been required just to build around the tunnel.

It would have been impossible to build that much additional track as there is not enough room at the summit at this location for an additional 2 1/2 miles of track using the elevations of the Tunnel #6 portals as a control.

—Ed Strobridge

4/29/2007 8:16 PM  
Blogger CPRR Discussion Group said...

From: "Wendell Huffman"

I have wondered why the railroad wasn't run somewhat to the south – generally along the alignment of the wagon road, intercepting the built-line east of tunnel seven. Westward on the wagon road from the point where the wagon road crossed the railroad east of tunnel seven, the wagon road doesn't gain much elevation. This is the original "Donner Summit." If they could have put the railroad there, they would not have had to add in all the extra track to gain the elevation. The problem may have been with the line east of the summit.

Ultimately, we have to trust the engineers who laid out the route. They were not dummies and they fully understood the cost and the incentives. I understand that the railroad did consider a temporary "shoo-fly" over the summit, and we just have to believe that they put the railroad at the best location available. And perhaps the word "available" reveals the answer. The company had to keep the wagon road running, though I'm sure they would have considered relocating their own wagon road if that would have solved the problem.

On a similar note, I have wondered why the railroad didn't use Henness Pass. It is lower by about 500 feet, and if I understand it from Jack Duncan's book, the route of the Pacific Turnpike – Dutch Flat to Crystal Peak (Verdi) – via Henness was about ten miles shorter than the company's Dutch Flat & Donner Lake Wagon Road via Donner. Having driven both routes, it certainly seems to me it would have been better. When you look northeastward from that overlook on Emigrant Gap, one looks along the route toward Henness Pass – past Spalding, Bowman's, to Jackson Meadows, and to Henness. There would have been some rough going west of Henness, but east of the pass is beautiful open country, quite different than the hard granite the CPRR had to scale down from Donner to the Truckee. The only answer I can imagine is that the Henness route was encumbered with at least one wagon road franchise before the railroad company came along, and perhaps it just wasn't available to them.


4/30/2007 9:18 AM  
Blogger CPRR Discussion Group said...

From: "Edson T. Strobridge"

There is a good discussion on the routes originally surveyed by Theodore D. Judah in George Kraus' High Road To Promontory (pgs. 34-38) and the reasons for selecting the route over Donner Pass. Interestingly, in a Footnote on p. 38 Kraus cites a report by William Hood "for many years chief engineer of the Central Pacific who declared in 1925 that in his opinion, Judah's reasons were as valid today as when Judah wrote his 1861 report. Were there now no railroad over the Sierra, Hood stated, the Donner Lake Route would still be selected over all others as the best possible route over the range."

I think one thing missing in this discussion is the consideration for the time line which was a driving reason for doing a lot of things that had to be changed later. Time and reduced costs of construction was the essence that drove many of the decisions that were made. That is one of the reasons that the Engineers had a fear of J.H. Strobridge as he had the ear of the Associates and when he saw a way to shorten the time and reduce the costs he did it whether the Engineers liked it or not. That was true until the day James Harvey Strobridge retired 1890.

—Ed Strobridge

4/30/2007 11:20 AM  
Blogger CPRR Discussion Group said...

Chris Graves mentioned that his research indicated that 240 Chinese worked constructing tunnel #6.

2/10/2010 8:28 AM  

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