Don’t really have time to go through the entire analysis, but here is the technical document I was referencing: Base Year Model Validation Technical Memorandum

I was looking at Figure 4-4 on page 43, which shows StreetLight origin/destination data and MRB model results for existing westbound traffic on the I-10 bridge. The chart shows origins of westbound bridge traffic as a percentage of total westbound crossings. The origin “superzones” are labeled on the chart, but you can find a map of the actual superzone locations in Figure 2-5, page 12.

I assumed, for the sake of argument, that the eastbound patterns are roughly the same (there might be some small variances in reality since some people take different AM/PM routes).

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I find it very hard to believe that the still remaining routes E-11-IV, F-12-IV, F-13-IV, and F-14-V, would have higher average daily traffic than the now eliminated C-7-IV route. I realize that's the conclusion that the slide that you linked to earlier states, but I am skeptical that whatever underlying data they used is correct.

To be clear, I wasn’t comparing the other south bridge locations in that post - I was pointing out the differences between a south bridge and a north loop to I-12. That being said, that model validation report should address your questions since this is the model they used to determine average daily traffic on the various proposed bridge locations.

A point that I think is a little interesting - they basically eliminated all of the C-xx-IV options due to low demand. These are options that cross between west-side approach “C” (north of Plaquemine) and east-side approach “IV” (Ascension Parish just south of EBR). However, the other “C” crossings that are further north on the east side were retained and had higher traffic projections.

It makes sense to me that the more northern routes on the east side have higher projected traffic, but I found it surprising at first that the C-to-Ascension routes were “low” ADT while the C-to-EBR routes were “high.” However, after some further investigation it appears that “low” is 24,200-29,900 ADT while “high” is >35,500 ADT. So there’s potentially not that much difference between those options. I would be interested to see the raw numbers from the model but I haven’t found them anywhere yet.

Regarding the routes south of Plaquemine, E-11-IV and F-13-IV were also projected to have “high” average daily traffic. However, they were projected to provide “medium” I-10 congestion relief (compared to “high” for the remaining routes north of Plaquemine). My best guess is that this is because the further south you go, the more traffic is diverted from the Sunshine Bridge instead of I-10.

Last point - it’s worth mentioning that the ADT numbers used for evaluating the various routes are 2042 projections. The document I linked above is the technical memorandum for the base year (2019) model validation. Here is the document for the 2042 model (no-build option; e.g. model validation without incorporating new bridge options). From what I can tell they basically built the traffic model based on current data, then used projected growth in the various regions to forecast to 2042. I haven’t dug too far into it but I’m guessing their forecasts show considerable growth in Ascension Parish relative to EBR.