Vehicle Physics in Simutrans Extended

Power and Tractive Effort

In Simutrans-Standard, there is a "power" setting for all vehicles, but there is no tractive effort setting. Also, all hills have the same effect on vehicles no matter how many consecutive hill tiles are climbed. All vehicles brake at the same rate. The physics model is only partly realistic, being a deliberate compromise.

In Simutrans-Extended, powered vehicles can have separate tractive effort (note that the tractive effort is the starting tractive effort, not the continuous tractive effort) and power parameters. Also, the more consecutive hill tiles that there are, the greater the effect of the hill on the vehicles. This approximately simulates hills of different steepnesses. Vehicles have adjustable air resistance to simulate streamlining. Vehicles have individual braking characteristics that affect how quickly that they brake and therefore how soon that they have to start slowing down. The physics model generally is set to be as realistic as possible.

This feature cannot be adjusted in simuconf.tab.

The aim of this feature is to provide realistic incentives for players developing transport networks: steam locomotives (which tend to have a lower tractive effort than diesel/electric locomotives) have distinct disadvantages compared with other sorts of locomotives, which prompted the development of electrified railways in some places as early as the 1900s, although the expense of electrification meant that only certain sorts of networks (mainly suburban networks, where steam's poor acceleration compared to electric was a more substantial handicap than on long-distance trains, and whose high capacity demand warranted the cost of electrification) benefited from alternative power until diesel locomotives became viable in the 1940s and beyond.

This feature should give players more interesting things to think about when choosing which type of vehicle to use for any particular sort of task. Also, this feature combined with the hills and cornering feature should make the sort of railway network that makes economic sense in the early years of the game (many corners, few hills) very different to that which makes sense in the latter part of the game (many hills, few corners), which should prompt players in the latter stages of the game to redesign their railways to meet changing circumstances. Also, the change with respect to hills sould incentivise realistic network design that involves gentler gradients. Further, the braking characteristics feature, when implemented in the pakset, allows the simulation of the fact that, in the early days of railways, the principal limit on trains' speed was not the power of the locomotives but their ability to stop in good time.

Cornering

In Simutrans-Standard, vehicles going around a corner have their "friction" increased, causing them to go more slowly. No account is taken of how sharp that the corners are: the same amount of "friction" is added for any sort of corner. It is not possible to have tilting trains in Simutrans-Standard.

In Simutrans-Extended, corners do not add friction: they impose a speed limit based on the inferred minimum radius of the corner given the scale of the pakset and realistic cornering speed limits for that radius. Tilting trains can travel around corners at higher speed than other vehicles.

Note that the extent to which corners of any particular type make vehicles of any particular type slower can be set in detail in simuconf.tab. It is also possible to set the "friction", although the default is zero. It is possible fully to restore the behaviour of Simutrans-Standard in respect of corners by adjusting settings in simuconf.tab.

The aim of this feature is to make cornering behaviour more realistic, and also give players more comprehensible incentives in relation to network construction. No longer will more powerful vehicles be able to take corners faster than less powerful ones simply because of their power. Corners will affect high speed transport far more than they affect low speed transport, so a network design that works early in the game may well have to be adapted as transport speeds increase. This will give players greater incentive to modify their networks as time progresses.

Braking

In Simutrans-Standard, all vehicles of all types brake a fixed distance in before they need to stop and at a fixed and rapid rate. Railway signals reserve paths for trains when a train reaches four tiles in front of the signal. Convoys slow down when they are cornering, but not in advance of corners.

In Simutrans-Extended, have a brake force value. The deceleration of convoys rate is calculated on the basis of their speed, weight, rolling resistance (which can, unlike in Simutrans-Standard, be defined individually in the .dat files of each vehicle) and brake force. Convoys will begin to so that they can stop in time, meaning that convoys with better braking will be able to maintain higher average speeds. Railway signals will reserve a path enough tiles in advance so that the train reserving them can continue without slowing for the signal if the path in front of it is clear. Convoys will also slow down in advance of corners so that they are travelling at the maximum speed permitted by that corner when they enter it. This code has been mostly written by Bernd Gabriel.

The aim of this feature is to provide more realistic handling of the physical properties of moving vehicles such as have an impact on the achievable speed of transport in any given conditions, including providing realistic incentives for better braking power, better signalling and fewer corners.

Note that it is hoped in due course to have a more sophisticated (but optional) system of signalling in which the spacing of signals and the use of distant signals would be relevant to the speed at which trains are able to travel, and that cab signalling or moving block signalling would be necessary for trains to be able to travel faster than a certain speed.