page_title: Comparison of train and tram tracks
section_title: Interoperability problems
hierarchical_section_title: Comparison of train and tram tracks / Interoperability problems
context_page_description: A railway or railroad is a track where the vehicle travels over two parallel steel bars, called rails. The rails support and guide the wheels of the vehicles, which are traditionally either trains or trams. Modern light rail is a relatively new innovation which combines aspects of those two modes of transport. However fundamental differences in the track and wheel design are important, especially where trams or light railways and trains have to share a section of track, as sometimes happens in congested areas.
context_section_description: At the junctions of train tracks, the gap in the frog or switch rail is wide.   So trams can be accommodated.
  The main problem with a train on tram rails is the relatively narrow width of frog and switch gaps and channels of the groove rails designed to accommodate the narrow flanges of tram wheels . The wider flanges of train wheels increase the risk of derailment at these points. On routes where train carriages are driven on tram tracks (as in the past in parts of The Hague), wider  grooves  are required as a compromise that is practical as wide grooved girder rail is available. A larger structure gauge would also be required   This was also done in Los Angeles and in Vancouver as well as elsewhere in North America. The usually or normally limited structure gauge, and tight curves, on tram tracks will also prevent trains from using tram tracks.
  In North America the groove would have to be a minimum of 2 ¹⁄₈ in (54 mm) wide and by extension, the maximum distance between the inside faces of the guard flanges of the grooved rails can be no more than 52 ¹⁄₄ in (1,327.1 mm), see below.	
  Quote: 
  Design tolerances
  Design tolerances that affect the lateral displacement of the body include the following:	
  1. Lateral tolerance between wheels and rails	
  Two types of flanges are permitted on railroad wheels - narrow and wide. The maximum
  lateral movement T1 possible for a new wheel set centered on in-gage track is a function of
  the flange type and is determined by the following formula:	
  CAUTION: Use only English Units in Formulas in this Recommended Practice	
  T1 = .5[gt-(gw+2fn)]
  = .59375” (15.081 mm)  for narrow-flange wheels
  = .375" (9.53 mm) for wide-flange wheels	
  Where: gt = standard track gage at a point “5/8” (15.9 mm) below top of rail = 56.5" (1,435.1 mm)
  gw = minimum gage of wheel set between backs of flanges = 53” (1,346.2 mm)
  fn = minimum thickness of new wheel flange = 1.15625” (29.369 mm) for narrow flange or = 1.375" (34.9 mm) for wide flange
  Note: The conversions are not in the original text and are for information only.	
  Quoted from "APTA PR-CS-RP-003-98 Recommended Practice for Developing a Clearance Diagram for Passenger Equipment 5.3.2.1 Design tolerances" (PDF). APTA.com. American Public Transportation Association. 1998-03-26. Archived from the original (PDF) on 2015-06-26. Retrieved 2015-01-17.
caption: Difference in form and profile of the wheel and the rail of a train (left, blue) and a tram (right, green).