[jcrawfordor]

Very common on US freeways for work to be performed at night even though it's barricaded during the day. The barricades are to keep traffic off of work in progress, actual work may require additional lane closures, traffic disruptions as trucks enter and exit, and safety scales with traffic volumes. Keep in mind, for example, that the permanent closure area is not typically large enough to stage equipment. That means that equipment and supplies need to be moved in and out of a laydown yard during work, which is very dangerous during normal traffic volume.

It also tends to be the case that price is reduced by scheduling work across multiple contractors with independent scheduling... so the cost savings come at the expense of idle periods while waiting for the next contractor to be available. Not a totally unaddressable problem but ultimately fast and cheap are, as usual, opposing requirements. Funding politics can also play a role here, very common that larger projects don't have all of their funding available at once, so they may sit idle while waiting for the next set of funds.