The highest speed for crossings in the U.S. is 125 MPH. If the speed is above 125, then crossings aren't allowed on that section of line. However, what's the highest speed limit for railroad crossings (aka level crossings) in other countries, such as Europe, Russia, Japan, and China?
Turns out there is a Wikipedia entry under Level Crossing that provide some answers for your question with sections on railroad grade crossings by country and continent. Some excerpts by country:
Japan: "As of 2011, there are in total about 34,000 level crossings in Japan. Many rail lines in urban areas have been changed to viaduct or underground tracks, and the number of level crossings has decreased." and
"However, 111 people is dead by crossing accident in 2010, 218 is dead by accidental or intentional hit at the train car in contrast."
Finland: "Finland's state railway system has almost 3000 level crossings, according to TraFi." and "In Finland the maximum speed for trains on the rails with level crossings is 140 km/h."
Netherlands: "There are no level crossings where trains routinely run at over 140 km/h.".
Norway: "From 1998-2008 the Norwegian rail administration (Jernbaneverket) removed about 1000 level crossings, leaving about 3500 still in use. 160 kilometres per hour (99 mph) is the maximum speed for trains over level crossings."
Sweden: "A train speed of 200 km/h is allowed in Sweden over level crossings, if there are gates and an obstacle detection unit."
United Kingdom: lengthy entry on the history of crossing and types of crossing barriers. "There are around 6,550 level crossings in the United Kingdom, of which about 1,500 are public highway crossings."
Oddly, there are no sections on France or Spain. Open for any experts who want to contribute info on those countries and others in Europe.
Mexico: "Mexico has also begun to install US-style crossing signals on some of its KCS de Mexico, Ferromex, & Ferrosur rail lines. Although the majority of rail crossings in Mexico remain with just a crossbuck and unsignalled."
Runway crossings: yes, there is a section on airport runway crossings. Several of which have been separated for rather obvious reasons.