The rail system was chosen because the cost of energy is not so great as with a bus system, because it is much easier to carry a great number of passengers by train than by bus or car, and because the noise and pollution is not so great as with buses and cars. 

原句含三个becausey引导的原因状语从句，三个原因状语从句本身有含有比较状语从句。句中有两处错误：第二个because之前应该加逗号；第三个原因从句中的系词应改为are。

这两个as with的用法是一样的。我只解释其中一个即可。

as引导比较状语从句，with在这里是in the case of的意思，表示条件：在。。。的情况下/对。。。而言。as从句省略了和主句相同的主语和系词，as在从句中作表语，with+名词作as从句中的条件状语。

The cost of energy is not so great as with a bus system

=The cost of energy is not so great as it is in the case of a bus system.

铁路系统的能源成本不像公交系统那么高。

The noise and pollution are not so great as with buses and cars. 

=The noise and pollution are not so great as they are in the case of buses and cars. 火车的噪音和环境污染程度均低于公交车和私人轿车。

整段翻译：

选择铁路系统的原因有三：第一、铁路系统的能源成本不像公交系统那么高；第二、火车运送大量乘客要比公交车和私人轿车容易得多；第三、火车的噪音和对环境的污染程度要低于公交车和私人轿车。

as for, as to和as with是三个很常用的短语介词（或成语介词）。

1.as for, as to "就......而论；至于......"，介绍新话题或对已谈过的事作进一步的说明，放在句首。这样用时，as for和as to没有什么区别；但as for似乎更常用一些。（摘自《现代英语惯用法词典》P. 101）

As for me, I'd rather stay at home. 至于我，我想我还不如留在家里。

2.以下三种情况要用as to。

1) 表示about“关于，有关”的意义。多放在句中，后接名词、代词或名词性从句。

He wrote to me as to his work and study. 他写信告诉我有关他的工作和学习的情况。

2) 表示according to“根据，按照”的含义。

They sorted the apples as to size and color. 他们按照大小和颜色将鸡蛋进行分类。

3) 表示in proportion to“与......成比例，与......相称”的意义。

Her expenditure is not as to her income. 她的收入和开支不相称。

3.as with“正如，与……一样”

As with what I said, he failed again. 正如我所说的,他又一次失败了。

As with all new ideas it met with resistance.和所有的新观念一样，它受到了抵制。

▲as is the case with常用来构成比较状语从句。例：

As is the case with a lazy schoolboy, Tom always leaves what should be done today for tomorrow. 正像懒惰的小学生一样，汤姆总是把今天该做的事留到明天。