Human behaviour is often the main cause of slow traffic.
Road hogging, frequent lane changes and not signalling all cause road users to have to anticipate one another's actions, resulting in indecisiveness and having to slow down.
I have frequently noticed individual vehicles hogging the first lane of expressways during peak hours, with dozens of cars lined up behind.
Cars often speed up to prevent others from merging into the lane, then return to a leisurely pace after doing so.
Motorcycles, especially foreign ones, believe they have a dedicated lane between cars. They horn aggressively at cars that are attempting to switch lanes and refuse to slow down to do let them do this in a safe manner.
They also use the road shoulder or zig-zag through traffic. This adds to the apprehension and stress other road users feel.
While Electronic Road Pricing does play a part in improving road conditions by distributing traffic to other roads, there is a limit to its effectiveness.
There are times when heavier traffic is simply inevitable, such as during peak hours.
Drivers get used to the cost, or the alternative route is too long or just as jammed as the expressway.
We cannot rely solely on economic behavioural control. More policing needs to be done to curb anti-social behaviour on the roads.