How to immunise against fund managers' charms

Sometime in the 1960s (maybe the 1970s), Mexico set about expanding its motorway capacity. As is often the case, though the political capital was there, the finances were not. With an election pending, an expedient solution was required. A bright young spark at the Ministry of Transport suggested re-marking the two lane highways as three lanes. Once implemented, the 50% increase in road capacity had an immediate impact, but the consequences for the accident rate were grave. Eventually, common sense prevailed. The policy was rescinded and the roads were put back to their original state...