# IRC:Tunnels

### From #openttdcoop wiki

A formula to calculate the required amount of tunnels or bridges required to cross terrain, without disrupting the flow of the Mainline. It can be queried via IRC.

The formula is;

where x is TrainLength, y is TunnelLength and z is SignalGap

or in a simpler form:

"Tunnels Needed = TunnelLength / (TrainLength+SignalGap)"

**Tunnel Length** is the average span ( a good value would be the tiles between split and join)

**Train Length** is the minimum TL expected on that line

**Signal Gap** is the same as the setting in the 'Signal GUI' --(This defaults to 2 for openttdcoop and is fixed as such in the bot calculations)

**Of worthy note;**

<@Mark_> you shouldnt use pbs or presignalling at tunnel entrances <@Mark_> just regular signals <@Mark_> YAPF will do the rest

On IRC you can use a command to calculate this for you using the following:

!tunnels <TrainLength> <TunnelLength>

You can also see the calculations step by step by using Narc's Page

for reference, the bot command is:

"math calc ceil(max( 2, $2 / ( $1 + 2 )))"