FRA rules on grade crossings

There's a lot of talk on a number of boards about high(er)-speed rail being held back by grade crossings, and a bit of confusion about whether FRA rules require speed limits at such crossings. Some say yes, some cite crossings they know of where trains don't slow down at all. Is there an FRA rule, and if so, where is it? Supposedly it's in the CFR someplace, but the CFR is HUGE and the online version's search engine hasn't helped. I find rules regarding grade crossings from a motorist's point of view, but what about the railroad's? Can anybody help?
Thanks.

no restrictions on speeds upto 110 mph
anything over 110 mph no at grade crossings.


http://www.access.gpo.gov/nara/cfr/wais ... v4_09.html probably around 230 rules or so