Tunnel Datum is a datum based on Ordnance Datum used in designing tunnels which pass below sea level. By using a lower datum as the base point, negative numbers can be avoided in calculations, eliminating a possible source of mistakes.
- for the London Underground, a tunnel datum of ODN − 100m is used; thus a depth of -60m is 40 m ATD (above tunnel datum)
- for the Channel Tunnel, a tunnel datum of ODN − 200 m is used; thus a depth of -60 m is 140 m ATD
Read more about this topic: Ordnance Datum
Famous quotes containing the words tunnel and/or datum:
“The only way to find out anything about what kinds of lives people led in any given period is to tunnel into their records and to let them speak for themselves.”
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