<P> Powell reexamined the evidence on the record and determined that the State failed to meet its burden of proof to show that there was any statistically significant difference in safety between the 55 - foot and 65 - foot trucks . Moreover, the statute could potentially create more accidents, by forcing shippers to use more small trucks to carry the same quantity of goods, or force truck traffic to bypass the State of Iowa, shifting traffic (and a higher incidence of accidents) to adjacent states . Powell further rejected the State's contention that deference to the state legislature was in order, because the statute created such a burden to out - of - state residents, and the legislative history of the "border - cities" exemption suggested that Iowa's real purpose in enacting this law was to discriminate against out - of - state businesses . </P> <P> Justice Brennan concurred in the judgment, joined by Justice Thurgood Marshall . He suggested a new, three - factor test for the Dormant Commerce Clause: </P> <Ol> <Li> The courts are not empowered to second - guess the empirical judgments of lawmakers concerning the utility of legislation . </Li> <Li> The burdens imposed on commerce must be balanced against the local benefits actually sought to be achieved by the State's lawmakers, and not against those suggested after the fact by counsel . </Li> <Li> Protectionist legislation is unconstitutional under the Commerce Clause, even if the burdens and benefits are related to safety rather than economics . </Li> </Ol> <Li> The courts are not empowered to second - guess the empirical judgments of lawmakers concerning the utility of legislation . </Li>

The state legislature of iowa enacts a transportation