A couple of things we could explore on these topics. The obvious impacts of roads and traffic are direct mortalities that we all see. Less obvious, but still very seriously degrading to wildlife communities, are the direct mortalities we don't see, because scavengers pick up a lot of the dead or wounded animals, the effects of noise, visual stimuli, and air pollution, the direct loss of habitat, and, with dirt roads, compaction of soils and/or erosion. Biologists have thoroughly documented the effects of all kinds of roads, and while some species actually do benefit in some specific ways, the overall effects are overwhelmingly bad.Russell, I understand the impact that roads have on salamanders and turtles and other amphibians and reptiles. There are public highways in New England (and I am sure, in New Jersey) where naturalists wait all night to help them cross so they aren't killed, because there's no other easy solution. I wonder if culverts can be installed to help this, on roads where closing would restrict too much access? And if there are specific roads that cut through critical habitat and migration routes, maybe they can be closed, especially if other roads that give access to the same area are maintained for registered vehicles.
"Just walk it" is pretty ableist. It is not feasible or desired to make every natural area accessible for people who can't walk or hike long distances, but it is discriminatory to take away access that has existed for decades without proof that registered vehicle access on a particular road is killing wildlife. As a hiker, I am in good shape and can walk it, but not everyone can. Taking away their access may even be illegal.
This has led to quite a lot of investment in strategies to design roads in ways that reduce some of the bad effects, and also strategies to reverse some bad effects via the installation of wildlife overpasses and tunnels, fences, and, as you say, in some cases volunteers to directly help crossing animals. Check out "Connecting Habitats Across New Jersey" here: https://www.nj.gov/dep/fgw/ensp/chanj.htm.
Studies that I have seen indicate that none of these strategies resolve the problems introduced by roads and traffic; they only reduce some of the bad effects. From the perspective of wildlife conservation, roads are just plain bad. The more roads you have, the worse the impacts. That's why no one should be surprised or offended when conservationists advocate for fewer roads. They're not trying to "lock up the land" or "close all the roads." They're just conservationists acting like conservationists. It would be most productive, in my opinion, for all of us to understand why they are advocating for the closing of some particular road, because, as you say, there may be "specific roads that cut through critical habitat and migration routes," and there may be other logical reasons.
I do understand that, if we ask why authorities are closing certain roads, and we are not given the reason, but are told, instead, to just walk, that's unacceptable. In the case of T&E species, they may not be able to give us the precise reason, because sometimes disclosing species-specific and location-specific information about T&E species makes the species more susceptible to unscrupulous collectors or even poachers.
I'm not sure how to address the issue of access for people with various disabilities. That's an important topic, and obviously extremely problematic in wilderness areas.