Meanings of high tunnel in English

So, that's out high tunnel threat area.

When he cast a light into the opening he could see that the waist- high tunnel was indeed sloping down.

The road was a long and very broad and high tunnel, along which big-wheeled machines drove noiselessly and swiftly.

As darkness descended once more, I heard Bobby scrambling over the raised threshold, feeling his way forward through the short, five-foot- high tunnel.