Elevated rail, even monorail, is considerably more expensive, but also provides far higher capacity. You can also increase capacity on a train line relatively easily with shorter intervals and longer trains, while a gondola's carrying capacity is essentially fixed.

Rough comparison between three recent 3rd-world systems:

- La Paz gondola: 3000 passengers per hour per direction (pphpd), ~$10m/km

- Mumbai Monorail: 10,000 pphpd, ~$20m/km

- BTS Skytrain, Bangkok: >30,000 pphpd, >$100m/km (on recent extensions)

Gondolas make sense in hilly locales where hurricanes are not a threat (like La Paz), they'd be a non-starter for both reasons in Miami.