The trench idea sounds a little "light" on the likely cost, but, interesting and potentially less costly....

Now, about that part about "In the year 2050"..... A bit cheeky, good shot with that one..... And, quite humorous...

Based on my "sad but true" "best professional experience" like with the irrational South Pasadena "nimby's" for a 710 freeway tunnel that would never have come within 170 feet of their precious little nimby City, above it (and drain massive volumes of cut through local street traffic congestion gridlocking the City and towns around it for a ten mile radius), I would suspect that the rich nimby's in Del Mar will go for that alternative when hell is actually frozen over and entropy ends the universe altogether. So 2050 is optimistic, as time itself will not have yet ended, and which is more likely to come sooner, than those folks ever accepting construction of that scale, in front of those homes on the Del Mar bluffs.... And, that would regardless of any clear benefits or cost savings to any of the rest of us.... Did I mention rich and "spoiled" nimby's, who don't care?

My old colleague Linda, and her agency knows of this "unsaid" political/nimby "reality" all too well from other LOSSAN projects. And, that her goal is to try to find consensus on a viable and doable technical option, which is also going to be a "politically acceptable" alternative, and not in finding ways to start a WWIII with really wealthy nimby's...

And, these purported trenching costs may not include the rest of the two track and/or 110 mph.s speed parts, including the work on DT for approach causeway and trestles, which will need to be rebuilt, as well as a significant major cut and grade separation by the old power plant/depot site and beyond the bluffs north to the race track.