Narrative analysis: The symbology of a road is clear and world wide. Roads are for journeying, for changing both location and status. In Lehi's dream, the road not only leads by the fountain, but the "large and spacious field, as if it had been a world." I personally suspect that this addition of "as if it had been a world" was a textual addition of Nephi, who appears to be less comfortable with the language of symbols than his father. Lehi, who apparently understood the symbols without the detailed exegesis Nephi later receives would likely have instantly recognized the road as symbolic of journey through this earth life, on the way to that which comes after.
The rod of iron is the guide along the road. Its role as a guide is more important than its structural rigidity. In Joseph Smith Sr.'s vision of what must have been a revelation of the same symbolic archetypes, the guide exists, but is of much more flexible stuff: "Of this stream, I could see neither the source nor yet the mouth; but as far as my eyes could extend I could see a rope, running along the bank of it, about as high as a man could reach, and beyond me was a low, but very pleasant valley, in which stood a tree such as I had never seen before." In the more modern dream, the guide function is fulfilled by rope. It is the concept of the guide that is important, and the emphasis on the "iron" may lead us to a conclusion that the guide is inflexible. That would be an unfortunate reading of the image.