To begin with, create a simple map with something to stand on, and space to put your traffic on. Now, you already have two choices: making your traffic drive in circles, or just from A to B. Create a track with the entity utilities -> utility_track. Now build a track the same way as you did the game track. Make sure you choose between loop and no loop before you make the track. Also, if you choose loop, be aware that the traffic will not be seen on the grey line, so make sure that that grey line is hidden behind a building. Also, make sure the track stays one horizontal line, if it goes up or down, so will the cars. About the arrows, the arrow that is sizeable is for the route, the other one is for the direction you're facing. Make sure you don't try too much crazy things with those, cause the results may disappoint alot!
The next step is to create a manager. Find the entity objects -> obstacle_mgr and place it wherever you want, it doesn't matter. Fill the name in of your utility_track and set your settings. I suggest just changing orient to true and leave the rest alone.
Our last step: the cars! Create the entity object -> obstacle and again place it wherever you want. Set your settings, but you can also just copy mine here. You can also check my demo map on traffic here
The trick of trains is to build them of the right size. With trains, I mean trains that are actually riding, that usually form a whole map (think of the train level in which you have to get to the front). In my demo map you can see what I mean.
Start by building everything that surrounds the train. Don't make obstacles yet, because they are build in a very diffirent way. Just build the road, the wall and a ceiling, which should be very high. Once you have done so, give them textures. Now these textures are special, because they should be moving, what would give the effect of a riding train. Now build the train. Make sure it's big enough for Duke to walk on, or to walk in. Don't mind my demo map, because it is too small. Do mind the way I have build the train. Now, the easiest part is done. We need effects: when duke jumps off of our train, he just glides over the road. Also, there is nothing to the map yet. To avoid the glide glitch, use a area_damage entity for Duke to die when he jumps of, or a area_force for Duke to be pushed back when he jumps off (which would make it seem that he is standing still). If you want to bring obstacles to your map, use a mover entity. I can't really give more detail to the entities now, since I currently have no access to PrismEd. I'm sorry for that, and I'll correct it ASAP.
You wouldn't say so, but conveyor belts are made in the exact same way as trains. How? When building a conveyor belt, use a mv_conveyor shader on it to make it look like moving. Use a area_force to make it look like Duke is being pushed in the direction the conveyor belt is moving and use a mover entity to add obstacles (like crates). Demo map, and entity details will come 'when they're done' ;)
More to come.
Special thanks to everybody at DNMPS (including me, hehe)