porous portal
Word Rarity
Rare
Frequency: Zipf frequency 3.28 in modern English
16
Scrabble Score
12
Letters
3
Syllables
8
Unique Chars
Meaning
noun
A type of extended and perforated tunnel portal on high-speed railways, designed to reduce the build-up of pressure when a train enters a tunnel at high speed.
Example Sentences
- "The Down line portal will measure 220 metres in length, while the Up line portal will be 135 metres long. Known as 'porous portals', they will (as the name suggests) be punctuated with holes. These holes or vents slow the build-up of pressure created by trains within the tunnels. The resulting pressure wave, if left unchecked, can produce a phenomenon known as 'tunnel boom', which is created by the piston effect. Porous portals have been used on other high-speed rail networks in Japan and France, but this is the first time they are being used in the UK."