what would cause my van to die suddenly at a traffic stop?

I'm not sure but since this is the 'same thing' as the Mercury Villager it is very possible it has the inertia switch or *fuel pump cut off switch* just like the Mercury Villager has .. That information will be in the owners manual.. Be worth looking into just to make sure..

why would you replace the fuel pump if no power was going to it?how did you check the fuses and relays?