二楼答得不错,congest （动词）或 congestion（名词）是最常用来形容交通拥堵的词.
唯一的瑕疵是,经常（always 或 often）和 偶而（occasionally）还是有程度上的差别.
我的建议是：
1.These two (roads / streets) are often congested.It's (awful/terrible).
2.We've (already) been stuck in traffic for three hours.
简洁点直接用 stuck in traffic 就行,无需加冠词 the；already 也是可加可不加 - 语法上都可以接受.