How are SRBs and solid rocket motors transported safely? Do they ever end up on trucks driven down public highways?

Question

The BBC News article The Rocket Scientists Mixing Up a Giant Firework begins with:

In a remote corner of tropical South American jungle, French scientists are mixing a ‘cake’ with a difference – a highly explosive rocket fuel for a new breed of space rockets.

and goes on to mostly talk about how to mix the ingredients and then bake them "like a cake" into a form ready to become an SRB.

Answers to If not constrained by underpasses, etc., would Falcon 9 have been less of a flying noodle? suggest that Falcon 9 rockets are driven down the road (on a truck of course) and this is confirmed by this answer, and photos of that happening are not uncommon:

• Why are these Falcon 9 1st stage bodies (apparently) wrapped in black plastic for transport?
• What support equipment is necessary to maintain a falcon 9 booster during transport after recovery?

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Question: But what about SRBs and solid rocket motors? Are they ever transported on public highways? Or are they considered too dangerous for that? If not, does it mean these "cakes" are always "baked" in close proximity to their intended launch sites?

note: While even the segments of the largest SRBs are extremely heavy and that might be a practical limitation to highway transport, there are smaller ones, and solid rocket motors are even used as parts of payload spacecraft as well (example below). So let's not limit answers to only those that are too heavy for public highways, and instead keep the focus on the safety of transporting solid rockets on public highways.

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below: Image of Orion 38 motor from Orbital ATK's Propulsion Products Catalog, borrowed from What inclination change could the 5th stage Orion 38 motor provide ORS-5 (SensorSat)?

Above could probably fit in a 1-ton pickup truck, but below is probably strictly off-road.

below: "Transporting the rocket boosters is a slow and steady process" (Credit: Esa) Source

Answer 1

A few data points:

• Shuttle SRB segments were transported by rail, from Utah to Cape Canaveral.
• Ariane 5 SRB: the top segment is filled in Italy at the Avio factory, then transported by ship to Kourou. Transport from the factory to the ship is by truck over public roads, unless the factory is right next to the dock, which I doubt. The 2 large segments are filled on-site in Kourou.
• Vega: empty stages are produced in Italy, and filled on-site in Kourou.
• Atlas V SRB were transported by road.

I haven't found any documents on SRB transport safety.

Answer 2

Not exactly public roads, but shuttle SRB segments were transported on roads inside of Kennedy Space Center (KSC).

New, loaded segments were delivered from Utah on trains directly to the Rotation, Processing, and Surge Facility (RPSF). After being removed from the railcars, they were processed and subsequently delivered to the Vertical Assembly Building (VAB) for stacking on a large wheeled vehicle called the Solid Rocket Motor (SRM) Transporter.

Spent SRB segments from the Shuttle program, after cleaning, were transported on trucks from the cleaning facility to the NASA KSC rail yard to be loaded onto railcars for the trip back to Utah.

All photos: NASA

Answer 3

The British can be an inventive lot, the Skylark sounding rocket

components and payloads are made in the UK and then flown to Australia by transport planes. These include a special dedicated “explosives” transport plane that carries the rocket engines to Australia fully-loaded with their solid propellant.