I'd like to explore the proposed and "being-built" designs for the barrier. Do you know where I might find any info?
There has been some concrete/steel debate about the barrier. I don't see why it has to be either one or the other. Perhaps concrete is better suited than steel in one region or vice-versa.
Concerns about exposed steel corrosion are a bit overblown. The border barrier is in the most(?) arid region of the US...very dry. This is not central Ohio where humidity in the summer, and dank, wet winter days gorge on unprotected steel not to mention the tremendous usage of road salt going all thermonuclear on bridge decks and the supporting steel structure. Vastly different environments.
Ever notice the rusty-brown colored bridge iron when traveling on US highways? In most cases that's not a paint coating...it IS rust. ASTM A-588 aka "weathering steel" is used here. It's allowed to "rust", and the way this steel is alloyed the rust forms a protective barrier halting further corrosion. Another benefit is A-588 has a substantially better tensile strength than common run-of-the-mill (see what I did there?) A-36 structural steel.
Hot-dip galvanizing appears to me to be the ultimate in steel protection as ten-of-thousands of electrical power transmission towers can attest to.
I have often thought that common ductile iron pipe, the material used in a gargantuan amount of water main systems, would be the way to go for the bollard execution. Ductile iron is tough almost to the point of having a rubbery characteristic. This bend without breaking trait lends itself superbly well to unforeseen underground thrust forces, AND this stuff is practically immune to corrosion. And I haven't verified this, but I think most of the base stock for casting ductile iron pipe comes from scrap metal. Nice enviro selling point, no? DI pipe is dang near impossible to cut with an oxy-acetylene torch although it can be cut via other means such as a cut-off saw and abrasive blade. DI is commonly cast in 18' lengths, but I feel quite confident a couple of domestic foundries would readily tool-up upon seeing the potential market for longer-than-standard lengths. Yes...8" DI pipe installed vertically, 8' of its length bedded in a concrete slurry wall and 25' exposed vertically above grade. Then slosh the pipe bollards full of concrete. C~C spacing TBD. Low-tech, enviro friendly, and would withstand most attempts at breaching with common machinery and tools.
Anyway, thinking about how this barrier gets pulled-off is quite exciting to me, so I really would like to see what designs are proposed and/or being used right now.