I was killing time on YouTube the other day, and came across a video of a shipping company moving a very long girder to a construction site. There were several points in the move that they had to block all traffic through an intersection (with one of the chase cars) for a few minutes in order for the truck to be able to swing around enough to make the turn.

Now, just to be clear, I wouldn't have a problem with this if I were in one of the cars that was inconvenienced for a minute. But I do want to know, is it, strictly speaking, legal? Is there something in their oversized vehicle permit (or whatever paperwork) that says "You can block the road"? Or is it simply a matter of practicality, where the police realize that they need to get the girder there somehow, and it would cost more time and money to ticket them for blocking the road than it would just to let them continue?

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    In what state? The authority of chase cars working for the construction company (as opposed to local police officers) may vary by state.
    – cpast
    Commented Apr 3, 2023 at 0:47
  • OT: seeing a very large carrier finagle a monstrous wind-turbine blade around a tight corner in Colorado was a sight to see.
    – IconDaemon
    Commented Apr 3, 2023 at 12:48
  • @IconDaemon I see wind turbine blades going north every other week on the highway where I live. Ok, the factory is a little south and they are building a large wind park north of me.
    – Trish
    Commented Apr 3, 2023 at 12:59
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    The largest one that I have seen videos of was a 7000 ton coal digger. Top speed 25mph. Not miles, meters. They are built where they are used and may be moved after 20 or 30 years to a new location. They don’t use roads :-) Any obstacles are removed first. To cross a motorway, the motorway is first covered with a meter of ground to avoid damage.
    – gnasher729
    Commented Apr 3, 2023 at 13:33
  • 2
    The Wikipedia page Oversize load answers many questions about this, and in the language lists you can find equivalents from non-English-speaking countries.
    – Stef
    Commented Apr 3, 2023 at 20:32

1 Answer 1


Oversize transports are known beforehand and have special permits.

The department of transportation/Federal Highway Administration provides information for oversize and overweight transports.


The Federal government does not issue permits for oversize or overweight vehicles. This is a State option.

Nondivisible Loads:

Permits may be issued by the States without regard to the axle, gross, or Federal bridge formula requirements for nondivisible vehicles or loads. Nondivisible is defined as any load or vehicle exceeding applicable length or weight limits which, if separated into smaller loads or vehicles, would:

  • Compromise the intended use of the vehicle, i.e., make it unable to perform the function for which it was intended;
  • Destroy the value of the load or vehicle, i.e., make it unusable for its intended purpose; or
  • Require more than 8 work hours to dismantle using appropriate equipment. The applicant for a nondivisible load permit has the burden of proof as to the number of workhours required to dismantle the load.

In this case, a super-long girder has its value from being a single item, so the state is allowed to make a special permit to exceed the normal regulations on weight and size. The regulations what is needed for a permit and what the permit allows is state specific.

Typically, the permit is single-use and bound to a specific day and route. It's also not atypical for the crossings to be closed by police before the truck convoy arrives. Even without a police escort, the special permit allows them to block the road in specific circumstances, such as taking a tight turn.

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    More generally, there are all sorts of reasons that can justify closing public roads for fast longer than "a few minutes"; there was a street in my neighborhood closed for several years to accommodate a construction project. Seen in that light, permitting a long truck to block traffic for a few minutes is not particularly surprising.
    – phoog
    Commented Apr 3, 2023 at 8:52
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    For an in-depth look at one such project and a bit of discussion on what is required, here is a video on the move of the space shuttle Endeavour from LAX airport to the California Science Center: youtube.com/watch?v=tVzgHvTuwdU :)
    – Frodyne
    Commented Apr 3, 2023 at 11:31
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    @Frodyne that transport had whole roads closed for days to facilitate the transport, and was so exceptional that they had planned the parking areas as exhibit-spots for more than a year in advance. Most transports don't rise to that sort of notoriety, but it is an example of how much work can be in such a move. But then again, we know of whole houses being moved in one piece through half the US.
    – Trish
    Commented Apr 3, 2023 at 12:38
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    The answer is generally valid for EU as well, oversize transport is managed at national level.
    – fraxinus
    Commented Apr 3, 2023 at 14:27
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    And don't forget that such transports quite frequently need to temporarily remove road signs, even lamp posts and traffic lights, to make room for the transport. I've seen them move around town here (I live near a site where very large pieces for ships and cranes are made) where at times traffic circles are temporarily covered in steel plating for special transports, divided roads have their dividers torn out for a few hours, overhead traffic lights are sometimes removed, etc. to allow larger than usual items to be transported.
    – jwenting
    Commented Apr 3, 2023 at 17:19

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