Transport Tycoon is an older game whose entertainment value is not entirely diminished.
Basics
The game is on a grid system; that is, buildings occupy one grid space, although larger buildings (train stations, airports) can occupy more. (More on them later.) The objective is to carry cargo between its suppliers and people who demand it, i.e. iron ore to a steel mill, grain/livestock to factory, goods to town, passengers/mail to town, etc. There are four different ways to transport things.
Road Transport
Transporting by road is unpopular. Infamous, even. Road vehicles are slow, have little carrying capacity, loading stations can only hold 2 vehicles at a time (Railroad stations, by comparison, hold anywhere from 1-9 (1 track) to 45 (4 track); also, removing roads is expensive. Because road vehicles can carry so little, their income on making a delivery is paltry. You need lots of road vehicles to transport everything an industry produces.
To place a road square: Select the direction (N/S or E/W) of the road placement. If you wish to create a straight road, click-drag start to end. If you wish to create a curve, click one side of the square; this will create a portion of road that reaches about halfway into the square. Then select the perpendicular road construction and do the same (in a different side.) This will create a curved segment as opposed to a T intersection.
There is more than one kind of loading station. There's cargo (Everything that isn't passenger traffic) and bus (passenger only). However, as mentioned before, they can hold only 2 vehicles at a time. Instead of queueing if they find a station full, vehicles keep driving and search for a road loop. They do not pull a U-turn unless specifically ordered.
Stations of the same type (truck/truck passenger/passenger) cannot be built adjacent to one another; if you built one not quite adjacent it is considered a seperate station and decreases overall traffic. Whichever one is more efficient will draw the vast majority of goods, leaving the other one - even though it's owned by the same company - dry.
There is only one thing for which road vehicles can effectively be used: Transporting passengers and mail. If you set up a bus network as a mass transit system (Several bus stations in one town, buses make rounds) the buses will eventually turn a good profit. (Transporting passengers to/from a city accelerates its growth.)
Trains
The game is ridiculously biased towards trains. They are fast, can carry more than anything else, and are relatively cheap. The biggest station you'll ever need (5x4) occupies less space than the airport (6x6).
There are 4 different directions to build train tracks: N/S, E/W, NW/SE, and NE/SW. Diagonal tracks cannot be constructed through click-and-drag; they actually appear horizontal on the screen but the grid is set at a 45 deg angle.
The train eventually evolves into the monorail and maglev which are not interchangeable.
Sea
Ships can carry the most traffic but also carry it with painful slowness. Later in the game, oil rigs are constructed offshore, and this is really the only time that sea transport has any cargo-hauling use.
If there are two cities both adjacent to a lake, you can set up a passenger ferry system that is reasonably lucrative; however, the ships themselves are somewhat expensive. If you can afford the startup investment (Which you can't in the beginning of the game) a ferry system will, within a couple years, have paid for itself.
Air
Air transport has some big disadvantages. It is completely worthless for anything except mail/passenger trafficking; also, the airport is extremely large and as a result difficult to place effectively.
Whereas other vehicle types in the game have a reasonable number of engines to choose from, airports have an almost obscene plethora of aircraft, 3 or 4 of which are less expensive to buy/operate and carry more than the alternatives.
Towns also rate your performance; destroying buildings lowers your rating. If they grow to hate you enough, they will not allow you to build stations on any land they have jurisdiction over.
This game was created by Chris Sawyer, who was also involved in the creation of Roller Coaster Tycoon.
Available now: Transport Tycoon Deluxe!