Car drivers get frustrated with trucks... especially when trucks attempt to "pass" each other with a 0.1km/h speed difference, blocking the passing lane for miles... that frustration leads car drivers to make risky moves to overtake trucks before they get blocked again or to make up for the delay the trucks caused them.

Our highways would move much smoother, and tempers kept much cooler, if trucks were barred from the left lane in 2 lane highways (like how they are barred from the left lane in 3 lane highways).