Average Taxi Cost per MileTaxi average cost per mile
Jamaican taxi riders have a unique white number plates and route names on which they operate, e.g. Ocho Rios to Montego Bay, and they calculate a fixed, standardized tariff for these trips, so there is no fear that they will be overcharged. In Jamaica the average taxi will have 4 backseat users, maybe 5 if there are small kids (children paying half price) and one (or two, in more remote areas) in the front driver's cabin, so a four-person familiy would fill the backseat alone.
Tariffs are laughably low.... for example, a trip from Ocho Rios to Montego Bay is only JA$400, it just cost JA$200 to get all the way from Ocho Rios to Browns Town (you turn off the coast road at Runaway Bay and head upcountry to Bob Marley's birthplace and last stop in Nine Miles) and it cost JA$140 to get from Oracabessa to Ocho Rios.
If you fill a car (5 passengers), then you don't have to rent a car specifically and it shouldn't be more than the 5 passenger combination tariffs at the applicable Jaamaican tariff, i.e. if you fill a car from Ocho Rios to Montego Bay, it should cost JA$400 x 5 = JA$2,000, although it is likely that you would be billed closer to JA$8,000 if you specifically rent the car, in "tourist tax" and because of the high price of natural gases.
Or you can take a taxi from a stop located along the motorway, or stop a taxi just by stretching your arms away from your side and bending your hands up and down to indicate that you are looking for a taxi.
Make sure the rider is on the desired itinerary and jump (or squeeze) you in and call you when you want to get out, unless you're going to drive out the whole islands and avoid being billed more than JA$400 per person on most one-way streets.