>>1822694Track geometry needed for 200+mph is different than a road planned for 80mph traffic.
The gradient may be excessive in portions of the highway ROW.
The median, if not wide enough, would need to be widened by moving existing lanes outward, which entail building 'new' lanes for the highway.
Existing overpasses would be a hindrance (pylon placement/overhead clearance) and most would probably need to be rebuilt at the cost of several million dollars each.
There is little median space available in urbanized areas.
Rail stations in highway medians are unappealing from the rider's perspective.
Maintenance of way becomes more difficult because the rail line in the median cannot be easily accessed by maintenance vehicles.
Finally, highways aren't a destination. People want to go to towns and cities along them, so route the rail line to serve them instead.
