The judge is NOT interested in what happened.
DO NOT LIE.
DO NOT GIVE ANY EXCUSE.
Speak as little as possible.
In case the judge asked for more, which is very unlikely if you plea guilty,
do:
if you forget what happened, say "I forget"
if you remember what happened,
a) if you did stop, say "I believe that I stopped"
b) if you did not stop, say "I am responsible for my action".
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If it is your first ticket, congradulations! You are now an experienced driver. If it is not your first ticket, go to buy an additional $100,000 life insurance.