I paved highways for 5 years. The people standing around are because there is a surprising amount of manual labor involved. One example that isn’t obvious is raking. Sometimes rocks slip through the cracks at the hot plant and the paver leaves big rocks in the hot mix. There need to be at least one guy just standing around looking at the asphalt to get the rocks out and throw in replacement hot mix between the first and second rollers.

Asphalt is mostly crushed rock, and you need different sizes of rock from fines to bean size. Part of the QA process is checking that the rock mix is composed of the right ratios and have enough faces to meet the spec. This is done with random samples from the asphalt as it’s laid down. They also check the temp, if it’s too cool it won’t work. So they mostly stand around. On the other side of the paving train is another QA where they use a radioactive density meter to check the asphalt after the rollers hit it, and they also take core samples along the joint to confirm the rollers are doing right.

Then there is a guy from DOT supervising. The State owns the roads, he’s there making sure no one is cutting corners and to coordinate the train with the supervisor of the crew.

Add in a couple more hands to rake/shovel (think guardrails etc) and it LOOKS like 5 guys working and 10 standing around but it’s 15 people taking turns in a continuously moving operation, often in live traffic