The rule only applies where a sign says so. Without one, you must wait for green, even if the road ahead is completely clear.
One of the most common misunderstandings on Thai roads is the belief that you can always turn left on a red light provided the way is clear. Plenty of drivers do it, and Plenty of drivers behind you will honk if you don’t.
It is not a blanket rule, and whether you may turn left on red depends entirely on what is posted at that particular junction, and the signs are almost always in Thai only.
The short version, before the detail: red means stop unless a sign permits the left turn. Where a sign does permit it, pedestrians and traffic from the right still go first. No sign means wait for green.
Section 21 of the Land Traffic Act B.E. 2522 requires drivers to obey traffic signals and traffic signs installed on the road, marked on the road surface, or indicated by an officer.
Section 22 (2) states that on a red signal, or a red sign bearing the word “stop”, the driver must stop behind the stop line.
The default position is therefore simple. Red means stop, unless something specifically permits you to proceed.
The three situations you need to recognise
A blue sign reading เลี้ยวซ้ายผ่านตลอด
White text on a blue background. This means left turns are permitted at all times, and you do not have to wait for the green light.
It does not mean you may turn immediately. You must slow down, give way to anyone on the crossing, and let traffic coming from your right on the main road pass before you go. The sign gives you permission to proceed, not priority over everyone else.
A sign reading เลี้ยวซ้ายรอสัญญาณไฟ
This means left turn, wait for the signal. No turning on red at this junction, however empty the road looks. You stop behind the line and wait.
No sign at all
Wait for the green light along with the traffic going in your direction, then turn.
This is the situation most people get wrong. The absence of a sign does not create permission. It means the default applies, and the default is stop.
When the road gives you conflicting information
Junctions in Thailand are not always consistent. You may find a blue sign saying one thing while the arrows painted on the tarmac say another.
The generally applied order of priority is the traffic signal first, particularly where there is a dedicated arrow for the left turn, then the markings painted on the road surface, then the blue advisory sign.
Those painted arrows matter more than most foreign drivers realise. They tell you what each lane may be used for, and a left-hand lane is frequently marked for both straight ahead and left turns rather than left turns only.
About being honked at
If you are stopped at a red light in the left-hand lane and the car behind starts leaning on the horn, you are not necessarily in the wrong.
Where your lane is marked for both directions, and you intend to go straight ahead, you are entitled to sit there and wait for the green.
Being pressured into pulling out before it is safe is how these junctions produce collisions. Thai road safety guidance specifically identifies honking at the car in front to force a left turn as a behaviour that causes accidents.
Penalties
Failing to obey a traffic signal or a traffic sign is an offence under the Land Traffic Act B.E. 2522 and carries a fine.
If the offence causes injury to another person through negligence, the penalty is significantly higher, and the driver may face a criminal charge of negligent driving and suspension of their licence.
This is general information, not legal advice. Local conditions vary, and enforcement is at the discretion of traffic police.
The story Turning left on red in Thailand: when it’s allowed, and when it isn’t as seen on Thaiger News.
