Originally posted by tim60 I thought the answer would be something like this. Our desire to cut cost in what we buy ripples back through the supply chain till some poor truck driver cannot even drive legally and safely and satisfy the boss. In England the motorway speed limit is 60mph for large vehicles and 70mph for cars. Some truck companies have decided it is cheaper for their drivers to drive at a speed a bit below 60mph on the road and all are speed governed to 60mph. It causes serious congestion on a 3 lane (each way) motorway when a truck doing 60 pulls out to the middle lane to pass a truck doing 58, and then when they hit a hill, maybe the one doing the passing loses ground on the 58 truck, even further extended the time blocking the middle lane of the route, allowing only one lane to pass at 70. Also, it is a requirement to only pass on the right, and when there are trucks ahead many people do not pull back to the left lane for fear of smoothly changing right to pass the next truck.
Split speed limits suck. Some, but not all US states have split speed limits, as do most Canadian provinces. In my opinion it is unsafe. As you point out the congestion caused by speed limited trucks creates unsafe situations. Add to that truck drivers who linger in the middle lane out of laziness (most say it is bothersome to deal with traffic entering and exiting the freeway), and things can be difficult at best.
Experienced drivers who also drive unrestricted trucks are constantly frustrated by these limited trucks, particularly when operating in a state without split limits. The refer to these slow rigs playing the slow speed passing game as a 'race'.
Here is a shot I took in Arizona, where the limit is 75, a CRST/Werner 'race'. It took me several miles to get by.
Another problem created by speed limited trucks is a phenomenon called 'cluster trucking'. This is where 3 or more limited rigs lumber along, completely blocking traffic. Bad enough in good weather, it becomes quite dangerous in periods of inclement weather, rain or snow. Very hazardous.
The next photo was in Iowa, where the limit is 70. These rigs were poking along at 60ish.