What is "vactrain"

n. A theoretical (l/en: maglev) running in (l/en: vacuum) tunnels.

A vactrain (or vacuum tube train) is a proposed design for very- high-speed rail transportation. It is a maglev (magnetic levitation) line using evacuated (airless) or partly evacuated tubes or tunnels. The lack of air resistance could permit vactrains to travel at very high speeds—up to , which is 5–6 times the speed of sound in Earth's atmosphere at sea level—using relatively little power. Vactrains might use gravity to assist their acceleration. If these trains achieve the predicted speeds, the trip between New Delhi and New York would take less than 2 hours, surpassing aircraft as the world's fastest mode of public transportation.

However, without major advances in tunnelling and other technology, vactrains would be prohibitively expensive.

Several articles published in China around 2010 claim that researchers at Southwest Jiaotong University in China were developing a vactrain to reach speeds of . However, closer examination shows that the many papers published at SWJTU never use the term vactrain, and instead refer to the ETT work of Oster, Zhang, and Wang.