Manual / Overlays

Low clearances

Where the height-limited structures are, banded by how much headroom they leave, so a diversion can be checked against them before it goes out.

What you are looking at

Switch on Clearance in the Layers panel and every recorded height-limited structure in the state is drawn as a small circle, coloured by its height band.

Two shapes, and the difference matters more than the colour:

• A filled circle — the limit is recorded as applying to the road itself.
• A hollow ring — it is not. The Road clearance block says so under its key: hollow = the limit applies to what passes under it.

A hollow ring covers two cases, and the popup tells you which one you have. Most of them are bridges, where the limit constrains whatever passes underneath — usually a different road from the one your bus is on:

This limit applies to whatever passes UNDER the structure — confirm which road before acting on it.

The rest are structures where nobody recorded which road the limit governs:

It is not recorded which road this limit applies to.

Hover or click any circle for its height, what kind of structure it is, its band, its name where it has one, and that sentence where there is one.

The block along the bottom of the map carries the key, a status line, and a ⚙ button for Height ceiling and filters.

The bands

The key prints those numbers rather than just the words, because the two lower boundaries can be moved by whoever set the deployment up. What the key says is what the map is drawing.

It also prints only the bands you could actually see. At the opening ceiling of 4.3 m nothing above 4.3 m is drawn, so the key shows three swatches rather than advertising a colour the map cannot produce. Raise the ceiling and the fourth comes back.

4.3 m is the law, not a preference. It is the general-access height limit under the Heavy Vehicle National Law — a vehicle taller than that needs a permit whatever any individual structure allows — which is why it is the line the overlay opens on and the one boundary nobody can move.

Every label describes the road. There is no register of your fleet's dimensions in this app, so nothing here will ever tell you whether your bus fits. It reports what the road permits; you decide.

The ceiling, and the two filters

The ⚙ opens two controls:

Show structures no higher than: ___ m. The ceiling. Only structures at or below it are drawn at all, and it starts at 4.3 m. The block's own note explains what raising it does:

Raising the ceiling shows more of the network, including structures a general-access vehicle clears — the 4.3 m default is the HVNL limit, not a preference, and the bands are drawn against it either way.

Hide bridges (limit applies to what passes under). The hollow ones, gone. Its own note is worth reading before you use it:

Hiding bridges leaves only the structures whose limit is known to apply to the road itself. It removes little at a low ceiling — the genuinely low structures are overwhelmingly tunnels, 149 of the 169 at 4.3 m — and a great deal at a high one, where bridges dominate.

Both are yours and both stick: the ceiling is which vehicle class you care about, not something you re-decide every time you look.

The status line

Under the key: 169 structures · under 4.3 m · bridges hidden · 12 Mar 2026.

What they do not mean

An empty road is not a clear road. Only structures at or below your ceiling are drawn at all. A corridor with no circles on it means nothing below the ceiling was recorded here, which is a much weaker statement than nothing low here. The ceiling is printed in the status line for exactly this reason — read it before concluding anything from an empty map.

A hollow ring is not a limit on your route. It is a limit on whatever passes under that structure. Acting on one without checking which road it governs is worse than not seeing it at all, which is why the app says so on the key, on every one of those popups, and here.

"General access" is not "your bus fits". It means the structure clears the legal general-access height. Nothing in this app knows how tall your vehicles are.

Grey is not "low" and not "fine". No height recorded means nobody measured it. A structure nobody measured is not a structure that is safe.

This is a survey, not a feed. The structures come from a periodic mapping extract, and the date on the status line is when that extract was built. It does not refresh while you watch, it has no "as at" time, and a barrier or a temporary gantry put up last week is not in it.

A missing structure is not an absent structure. The source records what has been surveyed and signed. Nothing here is a guarantee that an unrecorded structure does not exist.

It is not part of a shared view. Unlike the other overlays, whether this one is on does not travel in a link or a saved view — it is a standing reference layer rather than something you were looking at. Switch it on where you need it.

When it looks wrong

There is no Clearance tile. This deployment has not been given the road structure data. It is a build step somebody has to run — ask whoever administers the deployment.

The status line says Could not load — switch the layer off and on to retry. The structures did not arrive. There is no background retry behind this layer, so the message tells you exactly what to do.

A whole area has nothing in it. Check the ceiling and the Hide bridges box before concluding anything. Both narrow what is drawn, and both are stated in the status line.

It says the view is incomplete. A line appears reading More structures exist than were loaded — this view is incomplete. It is not expected to happen; if you see it, say so, because the map is drawing a subset.