Just a simple countdown that can be triggered either through chat or server console. All player vehicles will be frozen during countdown and unfrozen at "GO!". A countdown sound effect will be heard as well.
By default will count down from 5 seconds
/cd
You can also specify the number of seconds to count from with /cd <number>
/cd 10
When running the command like this, the number of seconds will be saved so that you just need to type
/cdthe next time.