Each BT when it is created automatically has a Failed Transaction Percentage measure created as well. You can view these measures in the system profile -> measures section. Although I am not sure whether you can create a dashboard that conditionally populates with entries like that if you want to just be notified when one of your BTs exceeds the 30% threshold you can set up an incident and add all the Failed Transaction Percentages as measures in the incident. If each of the measures has an upper threshold of 30% you can have the incident send you an email and this will help you to know which BT and when it exceeded your threshold.
A simpler solution would be to create a chart with all the measures added. Here you could see how their failed percentages trend over time.
I hope that helps,