Most flood advice is written for a car owner. A truck is the other end of the problem: a bigger engine, an air brake system with valves and a compressor, and a driver who has been told to deliver. This article sets out what Thai guidance does say, what it leaves out, and what a transport manager should put in writing before the water comes.
The short answer
- Thai guidance gives depths for cars and pickups. It gives none for a truck. Neither of the two Department of Land Transport (DLT) statements read here names a truck. They cover cars, pickups, electric cars and motorcycles.
- The depth figure for your truck is in the maker's manual. It depends on where the air intake, compressor and brake valves sit, which a general table cannot know.
- If the depth is unknown, the truck does not enter. A marked depth post is better than a guess.
- A truck that went through deep water does not go back to work on the next trip. It gets a check first, and the check is longer for an air-braked truck than for a car.
- Wet brakes need deliberate drying. Tap them repeatedly on leaving the water, then check they work before the next loaded run.
What Thai guidance says, and what it leaves out
| Water depth | What the DLT statements say | Vehicle types named |
|---|---|---|
| 5 to 10 cm | Passable by all vehicles, not at speed | Cars, pickups |
| Below 40 cm, or not above half a wheel | Can be passed slowly | All vehicles |
| 40 to 60 cm | Small cars avoid it. Pickups and large cars can pass with the air conditioning off | Small cars, pickups, large cars |
| 60 to 80 cm | Dangerous for every vehicle, do not drive through | All vehicles |
| Over 80 cm | Use another route | All vehicles |
Three things to take from it.
- The two statements differ. One is from 2022, one from 2024, and the threshold for small cars and pickups is not worded the same way. Use the ranges, not a single number.
- No row says "truck" or "trailer". "Not above half a wheel" is the only rule worded for every vehicle, and what fails first on a truck, the air intakes, the compressor and the brake valves, sits at a height that differs by model.
- The advice on technique is the part that does carry over. Low gear, steady speed, a larger gap, and tapping the brakes after leaving the water are stated for every vehicle.
Before: three rules to put in writing
- No entry without a known depth. Tell drivers and subcontracted carriers that an unknown depth means stop, call dispatch and wait or reroute. The cost of a wait is small next to an engine and an air system.
- Name who decides. If the driver alone decides, the pressure to deliver decides for them. Give dispatch or the transport manager the authority to say "do not enter", and say so in the carrier agreement. The contract side of flood days is set out in flood season: which Thai routes close first.
- Ask each carrier for the maker's figure for its trucks. Put it in the file next to the vehicle record. If the carrier cannot produce one, treat the depth as unknown and the rule above applies.
A dock can flood too. Bendix points out that a water-filled loading dock can damage slack adjusters even where nobody calls it a flood event, so a truck backed into a flooded bay at your site is worth the checks below.
During: what the driver does
- Low gear, steady speed, no stopping in the water. The DLT advice is a low gear and a steady speed so the engine does not stall, and driving slower also cuts the wave that hits other vehicles.
- A larger gap to the vehicle in front. Wet brakes lose effectiveness, so the stopping distance grows. The Australian regulator makes the same point about heavy vehicles in wet weather: longer braking distances, and brakes well maintained and correctly adjusted.
- Do not restart an engine that died in the water. Isuzu's advice for a submerged vehicle is key off, disconnect the negative battery terminal, cover the positive one, and not start it, because mud or debris may be in the electrical or intake systems and a start can cause a short circuit or engine damage. Bendix adds that a vehicle must not be started if water has entered the compressor or dryer through the air intakes.
- After leaving the water, tap the brakes repeatedly and let the engine idle a while. Both are in the DLT advice. The aim is to clear water from the brakes and the engine before a loaded run.
After: the check, in two levels
A truck that crossed shallow water and a truck that stood in it are different cases. This split is a working rule drawn from the sources, not a published standard. Write both down so a driver does not have to guess.
Level one: drove through, brakes got wet
- Confirm the brakes work normally before the next loaded run.
- Check the engine oil, axle oil and transmission oil for water, and the air filter.
- Clean mud and debris from the wheels, undercarriage and engine, and watch the road for debris and damage.
Those are the points in the manufacturer's list. A driver can do the first of them in the yard, and a fitter should do the rest.
Level two: stood in water, or was submerged
The truck comes off the road until it is checked. The procedure below is Bendix's for an air-braked tractor and trailer, in the order it gives.
| Step | What it is |
|---|---|
| 1. Identify the water | If unsure, treat it as salt water. Salt water is highly corrosive and strips lubrication |
| 2. Salt water | Replace brake valves that were submerged, and also the compressor, reservoirs, ABS relays, modulators, brake actuators and foundation brakes |
| 3. Fresh water | Power-wash, but keep the jet off exhaust ports and rubber and sealing parts, which it can ruin |
| 4. Air system | Do not start if the compressor or dryer took in water. Drain the reservoirs, mark and disconnect the connectors at each valve, check for water, blow dry air through lines and valves, and replace anything contaminated |
| 5. Glad hands and hoses | Check them. Water and dirt enter the brake system through unprotected glad hands |
| 6. Wheel-ends | Check for water in drums and between lining and shoe, check the brake chambers for water, and relubricate, including the slack adjusters |
| 7. Electronics | Download diagnostics from the ABS and stability controllers, and check the trailer connector |
| 8. Before service | Push each ABS wheel speed sensor back against its tone ring, then test the air brake system and ABS, and retest later |
One line from that list matters for the budget: if moisture or contamination is found anywhere in the air brake system, the guidance is to replace all the pneumatic brake components, because full disassembly is the only reliable way to clear it. That is real time off the road and a parts bill, and both belong in the flood plan.
What to ask the carrier for
For a truck that stood in water, ask for a short note: which water, how deep, how long, which level of check, who did it, and the date the brake and ABS tests were passed. This sits well alongside the records described in how to tell whether a carrier is maintaining its trucks, and it costs the carrier one page.
Where it goes wrong
- Using a car depth for a truck. The DLT figures were written for cars and pickups.
- Starting it to see if it still runs. This is the single step both the manufacturer and the brake supplier say not to take.
- Counting only the engine. Most of Bendix's procedure is about the air brake system and the ABS, not the engine.
- Fresh water treated as harmless. Fresh water is milder, but Bendix still sets out the same air system inspection. Water of unknown type is to be handled as salt.
- No record. A truck that was under water and went straight back into rotation is exactly the vehicle you will be asked about after an incident.
What to do this week
- Write a one-page flood rule with the three before-rules above, and send it to every carrier and driver
- Ask each carrier for the maker's depth figure for the truck models it uses on your lanes, and file it
- Name the person who can say "do not enter", with a phone number that is answered at night
- Define the two check levels and which one needs a fitter, so nobody improvises on the day
- Ask for the one-page post-flood note on any truck that stood in water before it is booked again
- Add the cost of a Level two check to the flood plan, as days off the road and a parts bill, so it is priced before it is needed