The yellow trap occurs when the timing of the amber lights (also known as "yellow" lights in the USA) is asymmetric for two-way traffic on a single road: when a vehicle is waiting to turn across oncoming traffic and receives an amber light from the traffic signal, the driver may assume that oncoming traffic also has received an amber light and proceeds with the turn, believing that oncoming traffic will yield the right-of-way on an assumed amber.
This phenomenon occurs when the timing of the yellow lights (also known as "yellow" lights in the USA) is not uniform for two-way traffic on a single road: when a vehicle is waiting to turn across oncoming traffic and gets a yellow light from the traffic signal, the driver may think that oncoming traffic has also gotten a yellow light and can proceed with the turn, assuming that oncoming traffic will give way.