In order to raise the glide path to safely avoid the overpass, the proposal is to extend Runway 11-29 by 350 feet at its eastern end, shifting the western end of its approach by that length. This would conceivably provide enough of a graduated slope to clear the overpass and the required 17 foot safe zone above the highest height of clearance. The existing eastern end would not be removed, just remain as sort of a dead zone.
The runway extension would require the acquisition of some wetlands at the eastern end in order to raise the grade level, but the amount of wetland acquisition would be less than 5 acres, and would be within the existing property controlled by the airport.
 |
| Aerial view of Lafayette Regional Airport with proposed displacement of Runway 11-29 to conform with proposed I-49 Lafayette Connector freeway (via Lafayette Connector website) |
The Louisiana Department of Transportation and Development (LADOTD) and the Federal Highway Administration (FHWA), who are the lead agencies for the Connector freeway project, have had constant and consistent discussion and interaction with the Federal Aviation Administration (FAA) concerning the potential impacts of the runway extension. FAA gave their initial approval to the current alignment and LFT adjustments as stated in the FHWA Record of Decision (ROD) in 2003 (downloadable here), and then authorized and approved their own standalone ROD for the airport modifications in 2008. (The full FAA ROD is downloadable here (pdf document).)
Due to recent changes in FAA regulations for wetland mitigation and construction standards, the current I-49 Lafayette Connector Conceptual Design Study and Supplemental Environmental Impact Statement (SEIS) process does include a reconsideration of modifications to the University/Surrey interchange to mitigate or avoid the need for the runway displacement. It is more than likely, however, that the displacement will be retained due to conditions that restrict modifications to the University/Surrey overpass.
Nevertheless, such developments haven't stopped opponents of the Connector freeway, who would much rather it be diverted to a bypass around the city, from decrying the possible impacts of the displacement.
One such devout critic is Michael Waldon, whom has dedicated an entire blog (Connector Comments) to documenting his opposition to what he calls "the Con"; and his belief that this freeway project would be the worst thing to happen to Lafayette. I respect his right to oppose this project, but when his arguments are reduced to disassembled claims and distortions of facts, there is a need to correct the record.
And in the case of Lafayette Regional Airport, Mr. Waldon is, as we say, way, way off.
The main thesis of Waldon's blog post challenging the Connector freeway and the LFT Runway 11-29 displacement falls upon the theory that the 350' displacement understates by a factor of three the need for a much longer and more destructive runway extension. Essentially, he rips upon the proponents of the Connector for building their project with no concern for "building tall structures next to your airport". Here's how Waldon summarizes his beef with Connector proponents:
SUMMARY: The I-49 Connector FEIS identified unacceptable risk due to failure to meet FAA flight path obstruction guidance, resulting from the proposed interchange construction adjacent to the Lafayette Regional Airport. Without documenting calculations or rationale, the FEIS stated that in order to meet these minimum safety requirements, airport runway 11-29 would need to be displaced 350 feet southeast toward Bayou Tortue and the Cypress Island Swamp.
My calculations, based on FAA guidance, arrive at runway displacement considerably longer than that presented in the FEIS. Here, following FAA guidance, I calculated that the required displacement is 860 feet. This significant difference brings into question the economic, environmental, and engineering feasibility of the displacement. Impact of this displacement on flooding, wildlife, and wetlands should be carefully addressed and documented by DOTD.
The public attitude toward airport safety should always be conservative and circumspect. The Airport's 1975 Master Plan concludes "Conditions at the airport's periphery make expansion of its land area difficult or expensive or both." Even beyond the impacts of runway displacement discussed above, it is simply inappropriate to choose to construct any tall structures on the periphery of our airport which is already severely constrained at its location. Tall structures like the University and Kaliste Saloom interchanges constrain future airport runway alignment adjustments, and impact the ability to meet current requirements and future safety requirements should FAA guidance on safety margins or approach slopes change for any reason.Let's analyze Waldon's objections more closely, shall we?
The interchange closest to the glide path of Runway 11-29, as noted, is the University Avenue/Surrey Street interchange. Under the proposed Connector profile, I-49 would cross over University/Surrey at a maximum height of 16 feet, sloping downward to grade level right near where the flight path of Runway 11 crosses the US 90/Evangeline Thruway/Future I-49 right-of-way. The 11-29 glide path parallels and is 200 feet to the south of the Surrey/University centerline. With the adjusted RPZ glide path, the "end" of Runway 11 would be adjusted 350 feet further down from the current endpoint. This picture (from Waldon's blog) summarizes the adjustment with respect to the current Thruway and Surrey/University.
 |
| Overview of Lafayette Regional Airport Runway 11-29, with adjusted endpoint for displacement (yellow line) and half of the Approach Surface. (via Connector Comments blog) |
 |
| Vertical profile of I-49 Lafayette Connector alignment at University/Surrey interchange near LFT (from 2002 Final EIS, via Connector Comments blog) |
You can see that the Runway Protection Zone minimum is set at 17 feet above the highest object height; which would put it generally at approximately 30 feet above the ground level of the runway at the point where the 11-29 glide path intersects with the Connector overpass. The RPZ is also sloped slightly to adjust to the slope of the grade of the overpass, thusly extending the RPZ height to cover the overpass as well.
However, that might even overstate slightly the impact to LFT. Here's a much more recent profile of that section of the Connector freeway, based on the approved Selected Alternative, that was developed in 2007 during the initial Corridor Conceptual Study.
 |
| Profile of I-49 Lafayette Connector @ University/Surrey interchange (from 2007 Conceptual Study, via Lafayette Connector website) |
As you can plainly see, the University/Surrey overpass is now a bit less steeply graded, and the University/Surrey centerline profile is depressed a bit; this must have been to reduce the height of the overpass as to relieve the penetration of the glide path. But, the height in general remains the same: roughly 30' counting both the height of the overpass and the maximum clearance of 16 feet for vertical clearance for vehicles using the freeway mainline.
It is here where Waldon goes off the cliff. First, he sets up the measurements for FAA and FHWA standards, which is accurate enough.
Finally, it is necessary to estimate the height of objects above the roadway. This could include signs, streetlights, and aircraft warning lights. The FEIS does mention this, and suggests that special signage and lighting may be necessary. Thus, I will assume that the height of the vehicles on the roadway will be the tallest objects above the roadway. There is no Federal vehicle height requirement for commercial motor vehicles (CMVs). Most eastern states, including Louisiana, set a CMV height limit of 13.5 feet on most highways. Louisiana does allow heights of 14 feet on designated highways, and oversize permits can be routinely issued for heights up to 16 feet 5 inches. Without specific guidance from the Louisiana DOTD, it is unclear what height should be assumed. Here, I will simply assume a maximum height of 15 feet for all vehicles and objects on the roadway.It should be noted that while Louisiana doesn't have specific height requirements for vehicles using its roadways, Federal Interstate standards do require minimum height restrictions of 16.5 feet for overpasses of freeways, and 20 feet of clearance for covered/tunneled sections. Since the Connector will be an Interstate built as part of the I-49 South extension to New Orleans, I can assume that it will be built to those standards.
Assuming the peak height at the interchange structure controls the required runway displacement, the calculation of length for the approach surface is now straightforward.The highlighted portion of Waldon's quote gives his game away. 60 feet??? Really? But, I thought that the height of the University/Surrey overpass was only 12 to 15 feet; how did Waldon get to 40 feet? Simply, he gets his interchanges mixed up. The adjacent Kaliste Saloom Road interchange with the Connector freeway and the frontage roads does indeed include a 40 foot high ramp that is needed to clear the freeway mainline, the adjacent BNSF/UP railroad line, and another high ramp. There is one slight little problem, though; the Kaliste Saloom interchange is nearly 3,000 feet away from the RPZ glide path of Runway 11-29; and the offending ramp drops down to grade level to split to connect with both the northbound Connector mainline and the northbound frontage road long before it gets to the Runway 11-29 flight path. Here's an overview, straight from the 2007 Conceptual Study:The interchange height plus object height has an elevation of 60 feet (45+15). Adding the FAA 17 foot margin of safety gives a total elevation of 77 feet. Subtracting the runway height which defines the primary surface elevation then gives a height of 40 feet (77-37). At a slope of 34:1, the length of the approach surface to the primary surface is 1,360 feet (34x40). At this point along the approach surface, the approach surface width is 1408 feet (1000 + 0.3x1,360), or 704 feet on each side of the extended runway center-line (Figure 3). Adding the 200 foot width of the primary surface at the end of the runway gives a total distance form the peak of the interchange of 1,560 feet. The present distance is estimated to be 700 feet, so the total runway displacement required would be 860 feet (Figure 4). This is 510 feet longer than the value asserted in the FEIS. This difference significantly brings into question the economic, environmental, and engineering feasibility of the displacement.
 |
| Aerial profile of I-49 Lafayette Connector @ Kaliste Saloom Road & University/Surrey interchanges & LFT (from 2007 Conceptual Survey, via Lafayette Connector website) |
As plainly seen from this profile, the Kaliste Saloom ramps are so far away from the Runway 11-29 glide path that it would take some very, very, very bad aircraft control for any plane to even threaten to hit even the highest overpass.
But, it doesn't stop Michael Waldon from using the Kaliste Saloom ramps for his equation which concludes that a much steeper gradient for 11-29 would require a much longer runway displacement (860 feet, compared to the 350' proposed in the ROD). This would require a much longer extension of 11-29 that would not only consume far more wetlands, but potentially threaten Bayou Tortue, a tributary that sets the boundary between the airport property and the surrounding wetlands. This is the proof that, in Waldon's eyes, disqualifies the Connector as a valid alignment, and justifies his belief that a bypass would be much better for Lafayette.
If we adjusted Waldon's measurements to reflect the reality of the University/Surrey overpass rather than his fantasy of placing the Kaliste Saloom ramps in front of the airport, they would be as follows:
Interchange height (16 feet) + maximum surface height (16 feet) = 32 feet (compared to 55 feet)
Add FAA 17 feet clearance zone = 49 feet (compared to 77 feet)
Subtract 37 feet for primary surface elevation height: 49 - 37 = 12 feet (compared to 77 -37 = 40 feet)
Length of approach surface to primary surface, using 34:1 slope: 12 * 34 = 408 feet (compared to 1,360 feet)
Add 200 feet overrun = 608 feet (compared to 1,560 feet)
Account for current 700 foot length of Runway 11-29: 92 feet of existing leeway (compared to shortage of 860 feet)
In other words, the existing Runway 11-29 is actually marginally suitable for adjusting to the glide path changes from the University/Surrey overpass, but it would be a rather tight fit. The 350 foot runway extension/displacement would certainly add the necessary margin of safety, and would be the maximum allowed that would least impact the adjacent wetlands and Bayou Tortue.
As I mentioned before, the recent changes in FAA regulations regarding construction of runways over wetlands has prompted the FHWA and LADOTD to reconsider modifying the University/Surrey overpass to possibly avoid displacing the RPZ glide path. (Listed as Potential Design Modification #10; the full list of proposed modifications can be found here.)Such a study, though, does not avoid the basic fact that, even with the wetland impact, the runway displacement would not be anywhere near the destroyer of Lafayette that folk like Michael Waldon would assume it to be.
No comments:
Post a Comment