Please tell me why it should be 4 blocks below ground

Because else you cna't build a path underground ¬¬'' The ground will 'delete' itself

Why not more thn 4 blocks down then?

at least 4...

thought I said that.

So....Say if you put 8 down it would make no difference? :blink:

Well, the path would be deeper (if you keep it level with the ground until you go underground. Else, no.

Another one:
You can use block brakes as a turbo, by having the 'brake' (read launch) speed higher than the speed with which the train passes the brakes.

That's one of my fav's^

Ace's extra building tip

If you're planning on making modern homes for neighborhood schemes, here's a tip.

You should always build under brick material. Brick buildings are by far, the best and easiest to make for houses. Also, I would recommend mixing it up with the glass set. For example;

Build a normal, first story house. Maybe add some extra corners and plants. Now, remove one part of the wall. Maybe, two adjacent walls. Take a 1/3 wall and place it where the other walls used to be. Now with the glass building set, take a glass 2/3 wall, and place it over the 1/3 brick wall. The silhouette should be red. Now hold down shift. If it's blue, place it. If it's red, move your mouse up a tiny bit until it's blue and place it right there. And you've turned a normal wall into a fascinating window!

You can also make small windows by have 1/3 brick wall on the ground, 1/3 glass wall above that, and another 1/3 brick wall on top of that, which is good if you wanna make two stories with different sized windows or something. And, put a fence around the perimeter to create a backyard look. Or, put some flowers in a 1 by 2 glass building in the backyard to create a greenhouse. And with other houses, recolor them using the paint buckets before placing walls on the ground. The options are limitless!

And that concludes my tip on building Modern Houses. I probably will upload a creation so you can see what it might look like. Ciao!