I don't know what you mean. The only way you could ever end up with a cheaper fare with a taxi is the sort of edge case you've hit - a single trip that happened to end up cheaper. And that must be an edge case, since even single trip cost is always lower for mass transit. Travel times and such may be worse of course, but not cost.
Even discounting single trip price, the more trips you make, the better and better mass transit scales. For example, take London - even if you do the brainless act of just tapping your card on every card reader as you go, you can only get charged so much: [1].
But monthly/yearly tickets are really where the cost effectiveness comes in. I was being very generous in my calculations above, I assumed you'd only travel 2x a day, to commute to work. But as soon as you've bought the ticket, all trips during its duration become effectively free, so there's no reason not to use the system as much as practicable.
For example, I've probably made around 40 trips in the last 3 days. That plus all my commuting trips this month puts my cost per trip on the order of pennies per trip. You just can't beat that for cost.
Mawr|3 months ago
Even discounting single trip price, the more trips you make, the better and better mass transit scales. For example, take London - even if you do the brainless act of just tapping your card on every card reader as you go, you can only get charged so much: [1].
But monthly/yearly tickets are really where the cost effectiveness comes in. I was being very generous in my calculations above, I assumed you'd only travel 2x a day, to commute to work. But as soon as you've bought the ticket, all trips during its duration become effectively free, so there's no reason not to use the system as much as practicable.
For example, I've probably made around 40 trips in the last 3 days. That plus all my commuting trips this month puts my cost per trip on the order of pennies per trip. You just can't beat that for cost.
[1]: https://tfl.gov.uk/fares/find-fares/capping