Especially if it's competing against other AI's it might be a strategy to lower competitor's profits.
Maybe I care too much about ethics, but I file that under unfair competition to on purpose use rail/road crossings to block road traffic. It is very hard for other AIs to do anything about it if they didn't build the road themselves. If it is my AI that built the road, I can (and do) replace it with a bridge when there is a bus/truck crash event, but if there is a fellow road AI that built the road and does not care about upgrading it to a bridge, then it is not so much I can do about it.
_________________My OpenTTD contributions
(AIs, Game Scripts, patches, OpenTTD Auto Updater, and some sprites)Junctioneer
(a traffic intersection simulator)