I’ve always read that freeways are too steep and turns too sharp for rail, but Brightline says newer European trains are light and powerful enough to make it up the Cajon Pass in the median of the 15, so let’s stop screwing around with a single track for trains in the median. Just take the leftmost lane in each direction. Most of the cost is right-of-way acquisition; let’s use the one we already have. It’ll be better than nothing.