Will it work? The number of people interested in carpooling is small, the number of those who have iPhones is smaller (though it also works on other smart phones), and the number who happen to be going in the same direction as others who have smart phones much smaller.
If gas were still $4 a gallon creeping up to $5 or more, it might work. At less than $2 a gallon, it’s a lot more iffy. Still, it’s better than spending billions on rail transit that also only works for a few people. Perhaps more important, the iPhone system also works for transit and vanpool operators.