Translation:That intersection was very dangerous.
There are two types of adjectives as far as I know, the な-adjectives and the い-adjectives. The い-adjectives decline (change form, in this case, change ending) if you want to negate or to change tense. な-adjectives don't change when negating or changing tense.
A sentence with an い- adjective can indicate the tense without conjugating です, (which is added for politeness, it does not change because the adjective is already indicating positive/negative and present/past sense of the sentence). The い-endings are:
い。Present positive. 高い (takai, is expensive/high). Present positive.
くない。Present negative. 高くない (takakunai, is not expensive). Also when only using a く ending without the ない part it becomes an adverb (highly, expensibly).
かった。Past positive. 高かった (takakatta, was expensive).
くなかった。Past negative. 高くなかった (takakunakatta, was not expensive).
な-adjectives remain without change, and we conjugate です to indicate tense and and positivity. Also some of these adjectives do not necessarily have a な-ending and may be confusing.
Just expanding what Ramon and kazukun said.
I am Japanese . I try to explain this sentence . In the most case when a sentence ends in the word 'た' it represents the past . In this sentence , the last chraracter is ' たです。' . 'です ' is polite expression in Japdnese sentence . I hope this explanation helps you . It is hard to explain in English .
あぶない is/will be dangerous あぶなかった was dangerous あぶなくない isn't/won't be dangerous あぶなくなかった wasn't dangerous
Remembering that the sentence will be future or present depending on context. If you have something marking a future time like 来月 (next month) it will be future, if not it will be usually present but it's context dependent so pay some attention.
I'm an Australian, but I would agree. An intersection is where two or more roads meet (and if you wanted to be pedantic, it would be the area traversed by vehicles where any two roads cross each other's paths), while a street corner is the land immediately next to the roads that bends at a significant angle, generally as a result of any intersections.
To my understanding, こうさてんrefers to this idea of "intersection", while "street corner" lines up more with かど.