[MertsA]

Er... I don't think you've completely taken into account what you're proposing. Due to the square-cube law, splitting a pipeline into two smaller pipelines means that in order to have the same total cross-sectional area you would need sqrt(2) times as much surface area. Not only is the surface area that is subject to corrosion increased, I would imagine the pipe wall thickness would probably decrease so corrosion would compromise the integrity of the pipeline even sooner. It's also double the number of welds that need to be made, double the length of pipeline to maintain, and as to the notion that it would do half as much damage, I doubt this claim. Why would it actually substantially decrease the damage to the environment? It's not like pipeline leaks completely sever the pipeline in half and just start inundating the surrounding area with a flood of oil. It's usually a crack or pinhole leak, so the smaller cross-sectional area of the pipe probably won't do much good in terms of decreasing the volume of oil leaking out.