How are rollercoster saftey standards created and tested for multiple rides holding hundreds/thousands of people a day? How are you able to put so much trust in this sort of engineering?
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You can test with worst-case loads: faster than operating speeds, loaded with additional weight beyond normal operating loads, to see if anything fails.
With regard to the design, these kinds of structural mechanics are very well known and characterized, like with bridges and other buildings. Most, if not all, structural failures stem from someone skirting recommended practices; not built to specification/subpar materials used, irregular/incomplete maintenance, operating outside safe conditions, operating longer than its life-expectancy, etc.
ASTM – American Society of Testing and Measurement – has a lot of standards written for this very purpose. They are focused on the design of mechanical equipment and take into account guests seating surfaces, traction, pinch hazards, guarding from moving equipment, reach envelope, etc etc etc. The amount of standards is quite exhaustive. ASTM is made up of professionals who work in those specific industries, often writing and re-writing the standards over decades.
Specifically for the multiple rides part of this question, there is something called ‘fatigue loads’ which takes into account multiple repeated loads. Materials and structures have been studied for years and years and ways have been found of predicting how strong the structure needs to be to withstand not just one load, but thousands and thousands of that same load. Structures and the materials they are made of can be put under many many repeated loads in a lab, putting the structure under as many individual load cycles as the rollercoaster or any other structure might experience during its life in a short period of time. After enough repeated experiments, which reliably match the predictive models, we can trust those models to reliably predict the max fatigue load for a new structure.
There are also ways of predicting how quickly a crack will grow, and how much a crack reduces the strength of the structure. Often the first signs of wear that could eventually lead to failure will be cracks that grow slowly over time, and if the structure is designed very well those cracks will be visible to inspectors well before they become dangerous. Basically, if you a small crack, it concentrates the load that would normally be spread over a large area onto a much smaller area, and leads to the crack growing. Structures like rollercoasters are sometimes inspected regularly, and if a crack is found it can be stopped from growing by drilling a hole at the end of the crack which redistributes the load and prevents the crack from growing further.
There are still failures sometimes, often due to someone making a mistake that incorrectly accounted for fatigue loads or stress concentrations, or because an operator cut corners by skipping inspections or ignoring signs of wear.
in addition to what everyone else has said, a lot of roller coasters (especially in smaller parks) are not unique. There are companies selling “off the shelf” roller coasters, where you basically only need to change the branding (names, colors, etc.). So if there are already 10 coasters of the same type existing, then there most likely is no inherent structural problem with it. Of course installation has to be done right, but that problem is not unique to roller coasters, so you can use generalized standards.
If you now have an actually custom-designed, one of a kind, roller coaster, you have to take a lot more steps to prove that it is safe. This part is already well covered by the other commenters
I was an engineer at Six Flags for a few years. The simple answer is that coasters are so over-designed that you don’t really need to test them. Every single component is at least 5x stronger than it needs to be, and a lot of them are 10x. Every beam, bolt, seatbelt, and gear has a rating of how much force it can withstand before deforming, and those forced can be calculated before based on the speed and weight of the trains. Now especially, everything is computer simulated before the first piece is even built.
We have been building lots of things for many years now. It’s not like we are just taking it on blind trust. This type of construction is well tested and understood at this point
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