Allow more vehicles in the game.
Configuration file: morevehicles
Command line: -x
This switch creates more blocks of data to store vehicle information in. Its value can range from 1 to 40, but it is good to start low (2 or 3) and only raise the value when you run out of vehicles. Each increase adds 850 vehicles, 160 of which are reserved for steam puffs.
Games saved with this switch set to more than one should not be loaded if you reduce the value of this switch. So, if you save a game with a morevehicles value of 3 should not be used if you change the value to 2. Games saved with this switch active use the names TRPxx.SV1 instead of the TTD standard TRTxx.SV1 to prevent classic TTD from trying to load them, which would cause it to crash.
In many games, it is easy to reach the maximum number of vehicles at 850. And 160 of these are reserved for other animated objects and steam or smoke plumes, so that the remaining 690 vehicles have to be shared by all human and computer players. And planes even count twice, because they carry both passengers and mail. (Helicopters count as three vehicles, because their rotor is also a vehicle...) This means that it is easy to run out of vehicles in games with many opponents.
This switch enables you to increase that maximum number, to more than 40,000 if you like. If you consider that there are only 65,536 squares in the map, it's obvious that this is more than enough. Vehicle memory is allocated in blocks of 850, and you specify the number of these blocks as a parameter to morevehicles. For example, morevehicles 2 allows you to have 2 times 690 vehicles, or 1380 vehicles, plus 320 reserved vehicles. Giving a factor of "1" is the same as not specifying this switch at all, and the maximum factor you can give is 40.
It is usually best to leave this switch set to a value as small as possible. Don't set it to 40 right away! Only increase the factor when you actually run out of vehicles. The reason for this is that this switch is not easily reversible, as opposed to all the other switches, and it will also slow down the game significantly if you use factors larger than 10.
Once a game has been saved with this switch set to a particular number, it should only be loaded with this switch set to the same (or a higher) number. Games saved with an increased number of vehicles will also get a slightly different filename. Normally, your savegames are of the form TRT00.SV1, with morevehicles set they will instead be TRP00.SV1. This will prevent them from being loaded by plain, unpatched TTD which would crash anyway.
It is always possible to load a smaller number of vehicles, so your old savegames can still be loaded. The program will simply fill the array with unused slots.
However, if you load a game that had the morevehicles switch set to a larger number than it is set to now, the patch may have to remove some vehicles in order to load the game. In that case, you will get a warning message that tells you how many vehicles had to be removed. The game will be paused immediately, so that you have a chance to check the game for missing vehicles before resuming to play.
Note that if any special objects or special vehicles were removed, you must check your game, whether it had a zeppelin crashed on an airport, or a UFO landed and waiting for a military plane or helicopter. In that case, the zeppelin or the military vehicles may have been removed, which leaves your airport blocked forever, and the UFO will never get shot down. Otherwise, the removal of special objects is generally safe, and means you will lose some steam plumes, diesel smokes or electric sparks, as well as the steam coming out of some power plants. In that case, you might want to remove and replace the power plant in the scenario editor.
All in all, this switch is pretty powerful, but also somewhat tricky to use. Experiment at your own risk, and keep backup copies of the original games if they are important to you.