Other Tips
  Vehicle Usage

With the wide variety of vehicles in TTD, it can sometimes be quite hard to decide which type of vehicle to use. This guide should help you make your mind up, based primarily on the default TTD vehicles. TTDPatch and OpenTTD have introduced the ability to use custom third-party vehicles, see below for more information on those.

Road Vehicles
Road vehicles are not the best for transporting large amounts of cargo over long distances because of their small capacity and speed. I only use road vehicles for passengers and mail between two close cities, and sometimes valuables, due to the limited production from banks. They can also be quite effective when set to go between opposite ends of a large city, encouraging city growth. If you can't fit a rail line to an industry, even after landscaping, you could use road vehicles as a feeder (piglet) to the nearest rail station. Generally though, road vehicles are best left to cover passenger routes.

Ships
I only use ships for oil rigs and in isolated areas. They are extremely slow and their large capacity and improved station ratings don't compensate enough to compete with a rail line. The new ships by Michael Blunck in TTDPatch 1.9 and higher are a lot better than the default TTD ones, and a passenger liner between seaside towns can be very profitable. If you have industries near the coast, you could link them up using ships, or you could even create canals, but you cannot expect the same sort of profit levels as you would get with trains.

Aircraft
Aircraft are good for passengers over long distances, but not much more. Their speed is great for across-map trips. Their capacity is too limited for cargo, although some of the high-capacity planes (such as the Boeing 747, or the Airbus A380 in the Planeset or AV8 vehicle sets) can be very profitable when refitted to carry goods over long distances.

I rarely use helicopters because they must stop at an airport to be serviced - I only use them to service oil rigs. Due to their speed, they take forever to land at busy airports as faster aircraft zip in front of them. In addition, helicopters disappear completely after 2020 or so, unless you use the enginespersist patch in TTDPatch, or one of the aforementioned aircraft expansion sets, which provide several new helicopter models.

Trains
Trains are unarguably the best form of transport in TTD. They have a high capacity and high speed. Their only disadvantage is a large amount of infrastructure is needed for a train line, and the hassle of upgrading from rail to monorail, and then to maglev (unless you use the TTDPatch sign cheats). Design tips can be found in the rail section.

New vehicles in TTDPatch and OpenTTD

Both TTDPatch and OpenTTD feature many new vehicle sets which can completely replace the original Transport Tycoon Deluxe vehicles. There are sets that offer more realistic vehicles (often based upon a national train system), or fantasy vehicles with larger capacities. You can find a much wider variety of trains, road vehicles, ships and aircraft in the form of GRF files, which can radically alter the way you play the game.

I highly recommend you investigate GRFCrawler and experiment with some of the new vehicle sets - they can add a significant amount of enjoyment to a game. Some of the more well-known and well-developed train sets include the DB Set XL, the US Set, the UK Renewal Set (UKRS) and the North American Renewal Set (NARS), although there are a great many more to choose from, so you'll be sure to find something fun to play with.

Trams

Both TTDPatch (2.0.1 alpha 68 or later) and OpenTTD (0.6.0 or later) add support for trams. Trams can be built both on open ground and on top of existing roads, and require a tram vehicle set for use. Trams can offer better capacity and reliability than road vehicles, but can be more expensive to build and maintain. They certainly add a new dimension to city passenger transport in the game, though, so it's worth integrating them into your transport network if you can!