OBU reference
Every alert your ERP 2.0 OBU can show you
Your OBU carries a fixed catalogue of road and traffic messages — speed limits, camera zones, accidents, closures, even National Day. Here are all 47 of them, in plain English.
Last reviewed September 2026
Where these come from
Alongside charging you, your OBU receives road and traffic messages and raises them as you approach whatever they refer to. Each message arrives with a category, a priority, and an icon drawn from a fixed set built into the unit — which means the range of things your OBU can tell you is finite and knowable. It is listed below.
We compiled this by going through the complete icon set in LTA’s published OBU developer library, which is the same interface the Gantry app is built against. Two honest caveats. First, you will not see all of these on a given drive — many are rare, and some are seasonal. Second, a handful of entries in the set have no unambiguous meaning; rather than guess, we have left them out.
Speed limits
The prevailing limit for the road you are on, shown either as a plain number or inside the familiar red ring.
| Alert | What it means |
|---|---|
| 40 km/h | Typically a zone limit — school zones, Silver Zones and similar. |
| 50 km/h | The default limit on most Singapore roads. |
| 60 km/h | Major arterial roads. |
| 70 km/h | Faster arterial roads and some expressway stretches. |
| 80 km/h | Common expressway limit. |
| 90 km/h | The highest limit shown on Singapore expressways. |
Enforcement and regulatory
Things you are being told about because getting them wrong costs money.
| Alert | What it means |
|---|---|
| Speed / enforcement camera | The camera-zone warning — the one most drivers say they actually want. |
| Bus lane | You are approaching a bus lane and its operating restrictions. |
| End of restricted zone ahead | The restriction you were under is about to lift. |
| No entry | Entry prohibited ahead. |
| Prohibition | A general “not allowed” sign, used where a more specific icon doesn’t exist. |
| Height limit 4.5 m | A clearance restriction ahead — mostly relevant to taller vehicles. |
| Directional arrow | A mandatory or advisory direction. |
Pedestrian and safety zones
Where the limit drops because of who is likely to be at the roadside.
| Alert | What it means |
|---|---|
| School Zone | Reduced-speed zone around a school. The same icon is also used for Friendly Streets areas. |
| Silver Zone | Reduced-speed zone in a neighbourhood with many elderly residents. |
Warnings ahead
The red-triangle family — something on the road ahead that you would rather know about before you reach it.
| Alert | What it means |
|---|---|
| Traffic jam / congestion | Queueing traffic ahead. |
| Accident | A collision or an overturned vehicle ahead. |
| Roadworks | Works in progress on the carriageway. |
| Vehicle breakdown | A stopped vehicle ahead. |
| Slippery road | Reduced grip ahead. |
| Water on road / spillage | Standing water or a spill on the carriageway. |
| Road cleaning | A sweeper working on the road ahead. |
| Tree-cutting works | Roadside tree works, often with a lane affected. |
| Road narrows | The carriageway narrows ahead — from the left, the right, or both sides. |
| Traffic light not in operation | A junction ahead is running without working signals. |
| General warning | A hazard that doesn’t have its own icon. |
Lanes and closures
What is open, what is shut, and where you are being moved to.
| Alert | What it means |
|---|---|
| Lane diversion or closure | A lane is closed or traffic is being diverted, shown for the affected side. |
| Road closed | The road ahead is shut. |
| Tunnel closed | A tunnel ahead is shut. |
| Slow | A blunt instruction to reduce speed. |
| EMAS | A message from the Expressway Monitoring and Advisory System. |
Expressway
Where the expressway network begins and ends.
| Alert | What it means |
|---|---|
| Expressway | You are entering the expressway network. |
| End of expressway | You are leaving it. |
Emergency
The ones you hope never to see.
| Alert | What it means |
|---|---|
| Ambulance | Emergency medical vehicles operating ahead. |
| Fire engine | Fire service vehicles operating ahead. |
| Accident / collision | A serious incident marker, distinct from the warning-triangle version. |
| SOS / emergency phone | An emergency telephone point. |
| Danger | A hazard serious enough to get its own marker. |
Events and public holidays
Singapore-specific messages for days when the roads behave differently. A pleasant surprise for most drivers — they usually don’t know these exist.
| Alert | What it means |
|---|---|
| National Day flypast | Shown around the flypast and its rehearsals. |
| Chinese New Year | Festive messaging. |
| Hari Raya | Festive messaging. |
| Deepavali | Festive messaging. |
| Christmas | Festive messaging. |
| Marathon or running event | Road closures for a running event. |
| Cycling event | Road closures for a cycling event. |
| Celebration or fireworks | A general event marker. |
| Event | A generic event message where nothing more specific applies. |
Two more things the OBU sends
Not every message is a sign. The OBU also raises two kinds of structured information that don’t fit the icon list:
- Car-park availability — a named car park and the number of lots free, for car parks near your route.
- Travel times — a destination and an estimated journey time in minutes, the same figures you see on expressway boards.
Seeing them is the hard part. All of this is only useful if it reaches you while you are driving. If you skipped the OBU touchscreen, none of it is displayed in your car at all — and if you kept it, it appears wherever the unit was fitted. Gantry Display puts these alerts on a round AMOLED screen you position yourself, with control over which categories appear and how long each one stays. See how it works.