“to build” or “to be built” or “to have built”

Question

In an English text book, I found the following sentence.

a. "The Swiss tunnel took 17 years to build." 

(The full article follows.)

"A tunnel" is supposed to be built, so I think

b. The Swiss tunnel took 17 years "to be built".

According to a native speaker, "a." is much better.

Is "build" a verb intransitive in the a.?

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In Switzerland, a train has made the first trip using the world’s longest railway tunnel. The tunnel goes through the Alps. It connects Zurich and Lugano.

The train left Zurich on December 11, carrying about 500 passengers. It passed through the 57.1-kilometer-long Gotthard Base Tunnel.

“This is a historic moment,” a male passenger said. “I really wanted to be part of it.”

At the end of the two-hour ride, the train reached Lugano. Passengers were welcomed by crowds and musicians at a train platform.

Answer 1

It's quite difficult to substantiate: "According to a native speaker, "a." is much better," but in this case, the Ngram program, crude as it is, actually provides some useful material.

Both forms are possible (and both are grammatically correct). However, according to Ngrams "is built" is much the commoner of the two variants, so could be considered, if not "much better", at least the preferred one in printed texts:

Answer 2

In your case , a) is indeed much better, because the tunnel itself took no part in the construction; it took [the tunnelling company, with their engineers and tunnelling machinery] 17 years to build it. A coral reef, on the other hand, might take some time to be built equally as well as some time to build.