That question sums up the problem some people are having in this thread.
What matters is the cost, and time, per mile of road. We've seen roadworks with no workers on-site, and we've been told that councils will hire a machine to do one stage of the job, on several sites, and complete that stage on all sites before they return the machine and hire the equipment to do the next stage.
Unless the labourers are all full-time, permanent, council employees, overlapping these stages, without any 24-hour working, would reduce the closure time without necessarily increasing the cost of the work.
The "Top Gear" stunt involved 24-hour working, and that would push up costs.
At the end of the day, the hire companies might need fewer examples of each machine, which wear out sooner. If their charges are related to the work done, the only difference this seems to make is that they have less capital tied up in hardware, reducing interest charges.
Of course this is a simplified analysis. For one thing, taxation rules on depreciation of assets are going to distort things.
It is, perhaps, worth comparing ordinary roads with the way similar work is done on motorways and trunk roads, where the funding and responsibility is differently organised.