As to shoulder use, a possible reason for only allowing during peak use is that you might only pay for a 'hot' tow-truck during peak use. So between 7-9 and 4-6 there would be a tow ready to remove any dead vehicle quickly -- where the rest of the time you'd rely on drivers just pulling over and waiting for the tow driver to wake up, shave, and finish their morning coffee.
Efficient use of assets is of value.
As to speed limits, I don't know why it matters. Perhaps a slower speed limit reduces the stop & go effect on freeways and increases throughput? [[Have you seen that video of cars in a circle and how they naturally head towards stop & go?
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