You begin at year 1950 if you play with the default setting. As you play more desings will become available. I think there is some randomness in all this but you will always get the new desings sooner or later.
It is usually always worth using the new desings especially with trains. They start at low % reliability but that increase with time when they are first created. This mean that if you get a new very powerfull train (in term of HP) but with around 50-60% reliability and you purchase a lot of them (and reduce the time for maintenance so they don't break so often) you can end up upping their % back up to the 90% and sometime more.
Since you get more money if you bring the good faster to the end of the line, this end up with profits in the long run. Plus the old models end up losing % realibility after a while so you should always consider trying new models to see if they increase or else your lines will be so bugged down with broken down trains that they will become less and less profitable until it's not worth it anymore.
For the trains hitting busses, that's not a bug and you can use this to your advantage. If you want to prevent this happening to your own vehicles tough be sure to create bridges above or tunnels under the tracks (for either the train or the road, doesn't matter as long as they don't both connect) or you can be sure it will happen sooner or later. When one of your vehicle crash (any kind) the % efficiency of the stations will drop to near 0 so you should always try to avoid that too.
And try to hit other players road vehicles too.
