This page lists data that has been made available from the rail and transport industry.

Network Rail

Network Rail Datafeeds, providing real-time train movement information from Network Rail's internal systems. You will need a reasonable level of technical skill to interpret the data.
The Sectional Appendix, containing detailed information of lines, routes, junctions and permitted speeds. This data is updated in June and December each year, and historical versions of the Sectional Appendix are available for reference
Working Timetables - schedules for passenger, empty passenger, freight and infrastructure trains.
Rules of the Route/Rules of the Plan, Data relating to planned engineering blockades and constraints on timetable planning.
Signalbox Opening Times
List of Level Crossings

Railway Safety and Standards Board

Railway Group Standards has current and withdrawn Railway Group Standards (the 'Rule Book'), Rail Industry Approved Codes of Practice (RACOPs), guidance notes and and Rail Industry Standards.

National Rail Trends, including Signals Passed at Danger (SPADs), volume of freight movement, historical Public Performance Measure data, passenger train revenue and temporary speed restrictions.

Passenger timetable data from ATOC in Common Interchange File format
London Terminals data from ATOC, detailing the valid London station used when travelling from a particular station
Fares data from ATOC - see Fares Data

TfL Developer Area, where you can sign up for access to numerous feeds, including live traffic camera images, real-time bus arrivals, Tube departure boards, station locations, a journey planner and tube disruption data.
Underground Working Timetables

Data.gov.uk details the route of the planned HS2 line. It is ESRI shapefile format. Licenced under Open Government Licence (OGL)

OpenStreetMap contains most of the UK rail network at varying levels of detail. Some stations are tagged with naptan:AtcoCode and/or a CRS reference, and some have routes associated with them. The Osmosis application could be used to pull nodes and ways from an OSM planet dump/extract.

Some of this data is fully open, other data is available for casual use but without clear licensing conditions.

SNCF Open Data is the open data project from French national operator, SNCF. The data itself is in beta (e.g. only covering some regions), with full open datasets anticipated soon.
NS API for all Dutch trains is a great, simple API including stations, schedules, and realtime feeds.
Zugmonitor API gives access to the data used for the Zugmonitor project. The API is only for non-commercial use, with full open data a question for Deutsche Bahn.
Irail is a Belgian non-profit initiative with the aim of opening up transportation data.
CKAN Spain railways data gives access to stations, lines and investments in Spain ADIF and FEVE. More information in Spanish
rata.digitraffic.fi offers open data about the rail traffic on Finnish rail network. The data includes all passenger, freight and work train schedules, estimated times, actual movements, train compositions and historical data. The service is provided by the Finnish Transport Agency. Currently the documentation is in Finnish only.