he bus he took is stuck in traffic.

他乘坐的公交车堵在路上。he took是一个省略了关系代词that 或which的定语从句，修饰限定先行词the bus，完整的定语从句为that / which he took，由于关系代词that / which在定语从句中作动词took的宾语，所以可以省略。be stuck in 困住，陷于。例如：They may be stuck in a traffic jam. 他们可能遇到交通堵塞了。be stuck in还有“卡住不动”的意思。例如：The car wheels were stuck in the mud. 汽车轮子陷到泥里去了。

If more roads were built, people would just fill them with cars again.

即使修建更多的道路，路上也还是会挤满汽车。注意，此句用了虚拟语气，提出一个与将来事实相反或不可能出现的假设，结构为：if从句用一般过去时，主句用“should (would，might，could) + 动词原形”，跟表示与现在事实不符或相反的条件句结构一样。例如：The air would certainly be cleaner if there were fewer cars on the city roads. 如果城市道路上少一些车辆，空气一定会更干净。（这个例句既可能表示与现在事实不符，也可能表示说话人认为将来城市里车辆减少的情况不可能发生。）He said he would not go to the party next week. If he went, would you go too? 他说，他不参加下周的聚会。如果他去，你也去吗？（假设他下周去，与将来情况不符。）

I think we should discourage people from using their cars in the city centers.

我认为我们应该劝阻人们不要在市中心开车。discourage sb. from doing sth.使某人丧失做某事的信心，劝阻某人不要做某事。例如：Teachers should discourage their students from smoking and drinking. 教师应劝阻学生不要吸烟、喝酒。

We should improve public transportation and encourage people to use that.

我们应该改善公共交通设施，鼓励人们使用公共交通工具。encourage sb. to do sth. 鼓励某人做某事。注意，encourage和注释12中的discourage是一对反义词，但两者的搭配不同，encourage 后面要用动词不定式to do，discourage后面要用名词或动名词。例如：His family encouraged him to learn music at a young age. 在他小时候，他的家人鼓励他去学音乐。She discouraged me from undertaking the work. 她劝我别承担那份工作。

I think it's unfair to make drivers pay extra money.

我认为，让司机额外付钱是不公平的。在“It is + 形容词+ to do sth.”句型，it作形式主语，代替由不定式to do sth. （或不定式复合结构for sb. to do sth.）所表示的真正主语。例如：It is important to learn English well. 学好英语很重要。

That's a good point.

说得好。/这点很有道理。good point常用于口语中，表示赞成别人刚说的话，意思是“说得好，好主意，有道理”等。

Car owners may probably be against it at first, but people who use public transportation will be in favor of it.

车主一开始可能会反对，但使用公共交通工具的人会支持。against是介词，意思是“反对”。例如：The voters are against taxes. 选民们反对税收。in favor of sb. / sth.是介词短语，意思是“支持，赞成”。例如：They wouldn't be in favor of income tax cuts. 他们不会支持削减所得税。