> You need medical equipment to handle all types of injury/trauma.
This is equipment that most hospitals already have for other reasons. It's not like they have ER MRIs that sit idle and then an MRI for everyone else.
Further, a lot of that diagnostic equipment simply isn't needed in most cases. For ER related problems, xray machines are commonly all that's actually needed. Those are fairly cheap in the grand scheme of things.
> You need physicians and nurses and supporting staff.
A lot of the need for that gets cut dramatically by having a single payer system. The reason we have big ERs is because they are required to treat before seeking payment. As a result, many uninsured and underinsured people are using the ER as a primary healthcare system. Give everyone 0 or low deductible healthcare and you'll see the number of ER visits drop dramatically.