I had the opportunity to drive through all five of the current PA Turnpike tunnels last week, and the trip brought to mind a question I've long had about the tunnels: What's the purpose of the roads that loop over the tops of the tunnel portals, and when were they added?
If you're unfamiliar with what I'm talking about, here's an example: https://goo.gl/maps/Qwho3sTfykB2
Note the dark asphalt lane that runs parallel to the through lanes then loops above and behind the ventilation building and back down the other side.
Every tunnel portal has this loop with the sole exception of the eastern portal of Kittatinny Mountain.
The obvious answer would be to provide service access to the ventilation equipment, but if that's the case, why wasn't this access provided (and assumably not needed) when the tunnels were originally built? And if that is the reason, why isn't one provided at the eastern portal of Kittatinny? (I assume if Kittatinny had only one set of ventilation equipment, its eastern end would have gotten a neutered portal like Rays Hill.)
Another thought is that they might provide a last-chance turnaround for overheight or hazmat trucks that failed to exit prior to the tunnel, but I'm not sure that large tractor trailers would be able to negotiate the sharp turn around the ventilation building–and especially not this particularly tortured curve (https://goo.gl/maps/gMUKBs6Tb6B2) at the eastern portal of Allegheny Mountain. And if the purpose truly was a last-chance turnaround, one wouldn't be necessary at the western end of Blue Mountain in the tiny daylight island between tunnels.
Current satellite photos appear to show a few marked parking spaces next to the loop road, although carving a road into the hillside would seem an expensive way to add a couple of parking spots.
As to when they were added: Photos seem to indicate that none of the tunnels had a loop road in 1940. It's hard to tell in old B&W aerial photos what's paved, what's a gravel/dirt access road, and what's displaced earth, but it doesn't seem these were added as part of the tunnel twinning either, at least not entirely. Looking at Penn Pilot aerial photos (http://www.pennpilot.psu.edu) for example, the western portal of Allegheny does appear to have some semblance of a loop road in 1967, fresh after twinning, but while the eastern portal has a clearing behind the ventilation building, it doesn't appear to connect to the road surface.
Anyone know more or have their own guesses?
Quote from: briantroutman on October 12, 2016, 12:46:21 AM
The obvious answer would be to provide service access to the ventilation equipment, but if that’s the case, why wasn’t this access provided (and assumably not needed) when the tunnels were originally built?
The tunnels were actually built to serve a rail line, not a highway. There was one tunnel in each location. This was around 1900 or so when they were built (I forget the exact year, but a few decades before the Turnpike was built). When the rail company went defunct (the rail line was never built), and Pennsylvania started considering a highway across the state, it was decided to use the abandoned tunnels. As traffic volumes grew, a 2nd tube was added in each location. However, even that's not totally true...in some cases the PTC decided to bypass the tunneled location (Sideling Hill being the most notable).
So the answer really lies in the history of those tunnels, from them not even designed to serve auto traffic, to having a 2nd tunnel built after the highway was opened. Those roads were probably added at some point just to make it easier to access the rooms and equipment.
This:
Quote from: jeffandnicole on October 12, 2016, 06:17:40 AM
Those roads were probably added at some point just to make it easier to access the rooms and equipment.
The loop roads don't really have anything to do with the tunnels first being intended for rail traffic, since the original (unfinished) rail tunnels were all enlarged (widened) significantly when they were adapted for use by the Turnpike. IOW, the original rail tunnels were obliterated. (The exception to that is the Allegheny rail tunnel which was abandoned in place while a new Turnpike tunnel was constructed virtually parallel to it just to the southwest.)
The loop roads are a relatively recent addition (as noted by the OP) simply for easier access to the support infrastructure.
I had always assumed that these roads were for getting from one direction of roadway to the other without having to cross through the median.
Whether that's right or not, I don't know for sure, but what I do know is that these sorts of roads are fairly common at large tunnels, for example the Eisenhower Tunnel in Colorado:
https://www.google.com/maps/@39.679146,-105.9044592,423m/data=!3m1!1e3
https://www.google.com/maps/@39.6787954,-105.9345564,256m/data=!3m1!1e3
The Eisenhower Tunnel ones are definitely used to turn around hazmats, as evidenced by the signs at either end of the tunnels (https://www.google.com/maps/@39.6812672,-105.8987593,3a,21.9y,265.83h,93.23t/data=!3m6!1e1!3m4!1sz5a01VlKhHi28u7xnIwbPQ!2e0!7i13312!8i6656). I assume the Pennsylvania ones are more for maintenance. Plus, it's easier for a hazmat vehicle approaching the tunnels to be intercepted due to the staffed toll booths at each entrance ramp.
Quote from: cl94 on October 12, 2016, 08:07:28 PM
Plus, it's easier for a hazmat vehicle approaching the tunnels to be intercepted due to the staffed toll booths at each entrance ramp.
Reminds me of an incident I heard on the scanner while traveling west on the PA Pike from Harrisburg East to Bedford in 2009. PSP radioed a BOLO to "all units" for a tractor-trailer (van type) carrying hazmat (exact cargo was never disclosed over the air). The reason they knew it was hazmat was, as noted in the BOLO transmission, because the driver, after going through the Bedford toll plaza, stopped and removed the placards off the trailer, then dumped them in a trash can. However, the driver was unaware that the plaza supervisor was watching the whole thing and apparently radioed PSP even before the driver got back in her truck and pulled away. PSP caught up with the truck just before they got to the Allegheny Tunnel.
The Lehigh Tunnel is a bad one to use for an example, as it was built brand new in 1957/1991 for the turnpike.
Quote from: SteveG1988 on October 13, 2016, 09:26:25 PM
The Lehigh Tunnel is a bad one to use for an example, as it was built brand new in 1957/1991 for the turnpike.
As near as I can tell from an aerial photograph (http://data.cei.psu.edu/pennpilot/era1960/lehigh_1958/lehigh_1958_photos_jpg_800/lehigh_102458_aqu_8r_33.zip) dated 24 Oct. 1958, Lehigh's loop roads did not exist when the tunnel was first constructed. It's hard to tell from the black and white photography, though.
I think the entire issue of the mainline tunnels having been "reused" from the South Penn Railroad is a red herring anyway. The tunnel work done by Vanderbilt's crew merely gave the PTC a head start: Some of the tunnels hadn't been completely bored through, all were lower and narrower than the Turnpike required, and Allegheny Mountain was deemed in such poor shape that it was bypassed entirely with a new tunnel.
For all intents and purposes, the PA Turnpike's seven original tunnels were practically new constructions in 1939. Had the loop roads been considered necessary back then, I'm sure the PTC would have constructed them.
Quote from: briantroutman on October 14, 2016, 01:28:27 PM
Quote from: SteveG1988 on October 13, 2016, 09:26:25 PM
The Lehigh Tunnel is a bad one to use for an example, as it was built brand new in 1957/1991 for the turnpike.
As near as I can tell from an aerial photograph (http://data.cei.psu.edu/pennpilot/era1960/lehigh_1958/lehigh_1958_photos_jpg_800/lehigh_102458_aqu_8r_33.zip) dated 24 Oct. 1958, Lehigh's loop roads did not exist when the tunnel was first constructed. It's hard to tell from the black and white photography, though.
I think the entire issue of the mainline tunnels having been "reused" from the South Penn Railroad is a red herring anyway. The tunnel work done by Vanderbilt's crew merely gave the PTC a head start: Some of the tunnels hadn't been completely bored through, all were lower and narrower than the Turnpike required, and Allegheny Mountain was deemed in such poor shape that it was bypassed entirely with a new tunnel.
For all intents and purposes, the PA Turnpike's seven original tunnels were practically new constructions in 1939. Had the loop roads been considered necessary back then, I'm sure the PTC would have constructed them.
I always thought that the railroad tunnels just provided the impetus to create the road "look, these tunnels are already built, half the labor is already done for them, just make them wider for cars and we should be good to go"
Since using the Existing railroad grading would provide a rather flat terrain route through the mountains, for the cars of the period. Even if most of it was bypassed. I could see the loop roads existing to allow for police turn around use. Allow for a higher speed merge into the slow lane if a cop has to whip around.
As a side note, SR 38 in Oregon has a tunnel for a rail line that was never built. One can also see concrete posts put up alongside the highway that were meant for the rail line. US 199 has the original routing going over the mountain that the Collier Tunnel goes through.
Rick
Quote from: nexus73 on October 31, 2016, 07:16:28 PM
As a side note, SR 38 in Oregon has a tunnel for a rail line that was never built. One can also see concrete posts put up alongside the highway that were meant for the rail line.
http://www.co.douglas.or.us/planning/hrrc/regions/pdfs/UmpquaRiverRailroadTunnel.pdf
Has a road tunnel ever been converted into a rail tunnel?
Quote from: NE2 on November 01, 2016, 01:30:50 AM
Quote from: nexus73 on October 31, 2016, 07:16:28 PM
As a side note, SR 38 in Oregon has a tunnel for a rail line that was never built. One can also see concrete posts put up alongside the highway that were meant for the rail line.
http://www.co.douglas.or.us/planning/hrrc/regions/pdfs/UmpquaRiverRailroadTunnel.pdf
Nice find NE2, nice! I did not know the story of how the tunnel came to be as thoroughly as the one in the link described.
Rick