There's no reason the grid must accommodate peak demand. Two other options are simple failure to meet demand (you only get 10 amps) and dynamic pricing to reduce demand (if air conditioning costs $100/hr you might not use it).
The costs associated with throttling/halting these sectors far outweighs the cost of overbuilt infrastructure. Electricity is already sold by the megawatt in "day ahead" commodity form so businesses have already priced this information into the market.
[1] http://en.wikipedia.org/wiki/Electric_energy_consumption#Ele... [2] http://www.eia.gov/todayinenergy/detail.cfm?id=10211
Can everyone dynamically shift business routines due to "demand"?
There's no particular reason emergency service shift changes need to be synced to the common business day -- indeed, my intuition would be that accident timing patterns would make this a bad idea independent of traffic impacts -- but there's also no reason that employers with employees for which they have strong fixed-time needs couldn't subsidize (or, in the case of public necessity where the employer is the government, exempt) their employees traffic fees.
> Can everyone dynamically shift business routines due to "demand"?
Yes, they can -- but, of course, there is a cost (which varies from situation to situation) in doing so. Of course, there's also a cost -- particularly an externalized cost born by others -- of traffic. If you effectively internalize the external cost (i.e., make it born by the people making the decision to engage in the action), then behavior should reflect the true costs and benefits resulting from the action.