People argue that heavy trucks require longer braking distances for any given speed, and lower truck speeds help equalize the stopping distance. On the other hand, opponents of lower truck speed limits have suggested that the differential speeds increase speed variance and therefore have a negative impact on highway safety. Our research demonstrates that it is likely that both of these arguments are correct.
The large number of safety studies indicates that this issue has received a great amount of attention. Unfortunately, many of these studies involve more advocacy than science. It's not that these studies aren't valuable, but they have problems with methodology, statistical analysis and even simple understanding of important terms, such as 'speeding.' In accident data, speeding is defined as both 'traveling faster than the posted limit' and 'traveling too fast for conditions.' Studies often do not differentiate between these definitions.