I don't know if there's a readymade tool for this, but maybe you could plot it as a collaborative map so that it's clear which drivers/passengers are close to each other? Something like https://felt.com/ might help. Like if you just plot everyone's neighborhoods, you can then draw shapes around each carpool.

Or there's this that I've used before, but I think it's really just a signup list and not something that automatically tries to geo-optimize your routes or anything: https://www.groupcarpool.com/#video_demo You can DIY something similar in Airtable, which is a bit nicer to use than Excel for something like this.