Indycar has an extensive instrumentation and safety program. The cars themselves are recording and sending thru real time telemetry, a large amount of data at all times. There is also a "black box" program that records crash parameters and forces. Additionally, drivers are fitted with head accelerometers (in their earpieces).
They regularly survive 100+G impacts, often hopping out of the destroyed car and into a backup after a medical; check. That said these are the spike/peak loads, which last for typically just fractions of a second.