Street works certification confuses people for one simple reason: you do not hold a certificate, you hold a set of them, and they depend on each other.
The three groups
Units fall into three groups.
LA — Location and Avoidance of Underground Apparatus. Everyone. This is the unit about finding what is already buried before you break ground: obtaining plans, identifying apparatus, using a locator, and digging safely around what you find.
O units — operatives. The people doing the work. O1 covers signing, lighting and guarding; O2 excavation; O3 to O8 the various kinds of reinstatement, split by the material being put back.
S units — supervisors. The mirror image of the O units, for the people monitoring the work rather than carrying it out. S1 monitors signing, lighting and guarding, S2 monitors excavation, and so on.
Key certificates, and why they matter more than the others
Three of these carry the rest.
| Key certificate | What lapses with it |
|---|---|
| LA | Every street works certificate you hold |
| O1 | Every other operative (O) unit |
| S1 | Every other supervisor (S) unit |
This catches people out. You can be perfectly in date on O3 — reinstatement and compaction — and still not be able to work on it, because your O1 expired last month and O3 depends on it.
The practical consequence: your earliest-expiring key certificate is your real expiry date. It is worth knowing which one that is, rather than tracking seven dates independently and assuming the nearest one is the problem.
Picking the units for the work you do
Operatives generally need LA, O1, and then whichever reinstatement units match the materials they work in. Somebody who only ever reinstates in hot-lay bituminous material does not need the modular surfaces unit; somebody laying block paving does.
Supervisors follow the same logic on the S side — LA, S1, and the monitoring units covering the work they oversee.
What the theory test looks like
Every unit is assessed the same way: 20 multiple-choice questions, 45 minutes, 16 out of 20 to pass. Units with a practical element are assessed separately for that part.
Because the format is identical across every unit, preparation transfers. Once you have sat one, you know the shape of all of them.
Where revision actually helps
The theory tests are not memory tests of the whole Red Book. They test whether you know the rules that matter and — for the open-book units — whether you can find a clause quickly under time pressure. That second skill is the one most people underestimate, and it is the one that rewards practice more than reading.
