question: Why are train tracks and wheels not build like gears?
comment: If they used gears on the tracks then there would be a lot of friction and a huge increase in how complicated things would be. Gears in a transmission or other applications often require a constant flow of lubricant. This is not possible on a track several thousand miles long.
passages: Some of the above requirements were a challenge for steam locomotive designers - "sanding systems that did not work, controls that were inconvenient to operate, lubrication that spewed oil everywhere, drains that wetted the rails, and so on.." Others had to wait for modern electric transmissions on diesel and electric locomotives.
  
  The above requirements disappear as the train picks up some speed because the frictional effort needed at the rails drops steadily with increasing speed and the nature of the wheel/rail contact patch changes as described below.
   Insulated blockjoints can be bridged by wheel scale in some circumstances causing one or two track circuits to fail. This problem may be reduced by having a pair of blockjoints in series about 4m apart. The short 4m section would not itself be track circuited.
  
  Section::::Failure modes and prevention.:Immunization.
  
  Electric locomotives must avoid generating noise in the frequencies that track circuits use. The SNCB Class 13 had such problems.
  
  Section::::Failure modes and prevention.:Transitory problems.
   In addition, the presence of track guiding the wheels allows for very long trains to be pulled by one or a few engines and driven by a single operator, even around curves, which allows for economies of scale in both manpower and energy use; by contrast, in road transport, more than two articulations causes fishtailing and makes the vehicle unsafe.
  
  Section::::Social, economical, and energetic aspects.:Energy.:Energy efficiency.
   BULLET::::- taking precautions when track maintenance work is performed in hot weather, and making sure ballast is sufficiently consolidated before full-speed operation is resumed.
   Hunting is a dynamic problem which can be solved, in principle at least, by active feedback control, which may be adapted to the quality of track. However, the introduction of active control raises reliability and safety issues.
  
  Shortly after the onset of hunting, gross slippage occurs and the wheel flanges impact on the rails, potentially causing damage to both.
  
  Section::::Railway wheelsets.:Road–rail vehicles.
   The permanent way trails through the physical geography. The tracks' geometry is limited by the physical geography.
  
  Section::::Intrinsic factors.:Types of vehicle.
   A disadvantage of fixed blocks is that the faster trains are permitted to run, the longer the stopping distance, and therefore the longer the blocks need to be. This decreases a line's capacity.
   Because of this imbalance the use of the sand distributor was very important. Each drive wheel could be fed with sand, in either direction of travel, by compressed air.
  
  Section::::Layout.:Electrical layout.
  
  The electrical part of the locomotive was adapted from the Be 4/6 12303, with changed components:
  
  BULLET::::- higher power output from the motors (4 x instead of 4 x over 1 hour)
  
  BULLET::::- electrical brake as on the Be 4/6 12313 and successors
   Generally the aim is for trains to run without flange contact, which also depends on the tire profile of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail. Either contact causes wear and tear and may lead to derailment. Many high-speed lines do not permit slower freight trains, particularly with heavier axle loads. In some cases, the impact is reduced by the use of flange lubrication.
   The primary challenge for modern rail maintenance is that less time is available to perform it due to higher traffic densities. Conventional rail maintenance machines (e.g. rail milling, planing or grinding) working at speeds from can work only during possession time (track closure) which is in most cases available only at night.
  
  HSG allows for working speeds of up to and is deployable within regular traffic.
  
  It comes under non-traditional machining operations.
  
  Section::::Principle.
   Freight locomotives are designed to produce higher maximum tractive effort than passenger units of equivalent power, necessitated by the much higher weight that is typical of a freight train. In modern locomotives, the gearing between the traction motors and axles is selected to suit the type of service in which the unit will be operated. As traction motors have a maximum speed at which they can rotate without incurring damage, gearing for higher tractive effort is at the expense of top speed. Conversely, the gearing used with passenger locomotives favors speed over maximum tractive effort.
   In a field test starting in 2004, the trains on the connection from the brown coal strip mine near Wählitz to the Schkopau Power Station were equipped with C-AKv-couplers which showed that regular wheel replacements shrunk below a third due to reduced wear. The solution has been kept and it spawned further investigations.
   The allowed unbalanced superelevation will cause trains to run with normal flange contact. The points of wheel-rail contact are influenced by the tire profile of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail. Either contact causes wear and tear and may lead to derailment if speeds and superelevation are not within the permitted limits. Many high-speed lines do not permit the use of slower freight trains, particularly with heavier axle loads. In some cases, the wear or friction of flange contact on curves is reduced by the use of flange lubrication.
   Due to the small size of Z scale and, in particular, the low weight of the locomotives (a small Z scale engine can weigh as little as ), it can be challenging to ensure reliable operation. In particular, the track must be kept clean, as minuscule particles of dust, dirt, or corrosion can easily stop locomotives. Poorly-installed trackwork can be a source of consistent derailing of rolling stock (although this is true, to some extent, in any scale). All of this can create issues for modellers who are interested in prototypical operationsin particular, switching.
   On routes that carry freight traffic in cars with the maximum allowed axle loads it will be desirable to set superelevations so that the balancing speed of each curve is close to the speed at which most such traffic runs. This is to lessen the tendency of heavy wheel loads to crush the head of either rail.
  
  Section::::Limit values.
   BULLET::::- The length of trains is limited to what will fit on the shortest stub track in the zig zag. For this reason, the Lithgow Zig Zag's stubs were extended at great expense in 1908. Even then, delays were such that the zig zag had eventually to be bypassed by a new route, opened two years later.
   The welded track was to be laid on six to twelve inches (15 to 30 centimetres) of crushed stone ballast, although this was not always achieved, and the bearing capacity of the formation was not always taken into account, leading to some spectacular formation failures.
   With the mass and power of locomotives like the Mallets, care had to be exercised in their operation. A light Mallet used as a pusher naturally connected to the train with its front coupler, and the strength of this drawhead was not infinite. While the engine could not push hard enough to break the drawhead, the engineer needed to avoid slack. On the downhill part of one run one day on the Buffalo Division from Beaver to Hoyts, the pusher engineer did not keep up with the train ahead and saw it pull away from him with his drawhead hanging from the last car.
   BULLET::::- Devise the optimum sequence of rolling stock items in a train, so that it can be efficiently assembled at its starting point and decomposed at its destination(s).
  
  BULLET::::- Devise a means by which two long trains can pass each other on a single track, for example the double saw-by manoeuvre at a passing loop, used when both of the trains are too long to fit into the loop. It may or may not be required to maintain the original sequence of rolling stock in each train.
   If weld repair of side-worn switches is undertaken, it is possible for poor workmanship to produce a ramp in the profile in the facing direction, that deflects an approaching wheel flange on to the rail head.
  
  In extreme situations, the infrastructure may be grossly distorted or even absent; this may arise from earthworks movement (embankment slips and washouts), earthquake and other major terrestrial disruption, deficient protection during work processes etc.
  
  Section::::Causes.:Flange climbing.:Wheel-rail interaction.
   Railway lines in desert areas affected by sand dunes are sometimes built on alternate routes so that if one is covered by sand, the other(s) are still serviceable.
  
  If the standard track centre is changed, it can take a very long time for most or all tracks to be brought into line.
  
  Section::::Description.:Regulations.
   Where one or more of the lines meeting at the junction are multi-track, the presence of a triangular junction does introduce a number of potential conflicting moves. For this reason, where traffic is heavy, the junction may incorporate flying junctions on some, or all, or the legs of the triangle.
  
  Section::::Considerations.:For turning equipment.
   Section::::Steam locomotives.:Response of wheel to hammer blow.
  
  Since the rotating force alternately reduces the wheel load as well as augmenting it every revolution the sustainable tractive effort at the contact patch drops off once per wheel revolution and the wheels may slip. Whether slipping occurs depends on how the hammer blow compares on all the coupled wheels at the same time.
  
  Excessive hammer blow from high slipping speeds was a cause of kinked rails with new North American 4-6-4s and 4-8-4s that followed the 1934 A.A.R. recommendation to balance 40% of the reciprocating weight.
   BULLET::::- Z-Bend Track, uses a double-track mainline running down both sides of a module. Modules can be of any length or width in the middle and any overall shape. The "standard" called Z-Bend Track applies only to the last of the module's interface to other modules, the electrical interface and the module height.
  
  Section::::In popular culture.
   A more complete analysis, taking account of the actual forces acting, yields the following result for the critical speed of a wheelset:
  
  where "W" is the axle load for the wheelset, "a" is a shape factor related to the amount of wear on the wheel and rail, "C" is the moment of inertia of the wheelset perpendicular to the axle, "m" is the wheelset mass.
  