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How much power is generated by dynamic braking?

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the rule of thumb for air insulation is 1" = 10KV, in clean environments (like offices or labs) the roof of a tunnel with diesel-powered coal trains rumbling through it at all hours doesn't strike me as the cleanest environment. . . So let's cut that back to 3" = 10KV. So, if we take a "standard" transmission line voltage of 25kVac, apply the RMS correction (root 2), and we're looking at 1 foot clearance from the tunnel roof, and a further clearance of 1 foot from the doublestacks. . . Which probably have the occasional corona point (a deep scratch will do) and all sorts of other crap on top of them. (dirty snow comes to mind) So add another couple of inches for safety, Hey, presto, Dave is right- third rail is the cheap and easy way thru tunnels. That, or limit 'Wire Hybrid" to a smaller loading guage. (not the best way to gain wide accepance) So we can look at the poly. Plastics attract dirt. (just ask any model railroader about dirt and plastic wheels) Dirt may insulate at 12Vdc, but I'm here to tell you that it conducts pretty well at 30kV. . . . So you'd need a LOT of poly to increase the leakage path to the point where flashover would be minimal even with the dirt. Then you have to worry about all the hot, carbon-laden gas coming out of the exhaust stacks of the diesels and melting the poly, or worse. Which brings up a point I hadn't thought of: Diesel soot (carbon and traces of sulfuric acid) on the caternary insulators and wire. . . I wonder what the solution was in the steam days when you had steam under the wire? Still sounds cheaper to do the third-rail thing . . . or follow dldances's theory and bull through on diesel power alone and put the pan back up on the other side. Cheaper still except for the odd crew that doesn't get the pan down fast enough. Or go to the opposite extreme and prohibit diesels from anything other than idle in the tunnel, and run on the wire. The pull-the-pan option seems cheapest to me. . . No fiddly high voltage troubles at all. My goal here is to try and think out a (relatively) low-first cost way to improve the energy efficiency of railroading. . . I think I'm talking myself out of the Diesel-Wire hybrid idea. (come to that, railroading is pretty fuel efficient except for the idling part. maybe that's the thing to go after, not the Dynamic brakes. . .EMD and GE seem to think so.)
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