Updated April 2016
Although there is considerable variety in the road transport available, most of it is not recommendable for visiting tourists. Navigating Santo Domingo in its buses is a real challenge unless you speak the local languages or you know the city well. A few years ago, the Government introduced modern air-conditioned buses, but these soon deteriorated and lost their appeal. Some of these are express, inasmuch as they make fewer stops. There are also those without air-conditioning that are cheaper. Fares vary with the type of bus and the distance, but you can go from one extreme of the city to the other for about RD$30 .
Guaguas and Carros Publicos
There are privately owned minivans (guaguas) and cars (carros publicos), mostly in a very bad state of repair, that pick-up passengers anywhere on their route, packing them inside, often beyond its seating capacity, making for very uncomfortable trips. Guaguas operate along main roads during the day only; carros publicos work well into the night. The fare depends on the route and should be around RD$30 to RD$50, for distances that might go as far as Boca Chica, the other side of the airport.
For a real, exciting (and dangerous) adventure there is a further form of public transportation: the motorcycle taxi, locally known as a motoconcho. They have the advantage of being able to weave in and out of traffic to avoid traffic jams and getting to the destination quicker, if at the risk of ending up in hospital! The cost is not fixed but will be approximately RD$50 for a ride in Santo Domingo.
They are limited to the outlying neighborhoods. You won't see many in the centre.
The Santo Domingo Metro is a project for a 6-line grid, below and above ground, designed to alleviate the traffic congestion on the city's streets. Line 1 has been completed and runs in a north-south direction. Line 2 meant to run east-west has been partially opened, going from station Maria Montez, to station Eduardo Brito crossing Line 1 at "Centro Olímpico Juan Pablo Duarte" where it provides an underground interchange. The extension of Line 2, as far as Carretera Mella, is expected to go into service in 2016.
The Metro is open from 6am to 10:30pm every day, and the frequency, although it depends on the line and time of the day, should be between 5 and 10 minutes. A single ticket costs RD$35; return RD$55 (this is made up of the cost of the paper ticket RD$15, to which is added the cost of the journeys: RD$20 each way. This ticket is not rechargeable). A day pass costs RD$80 + RD$15. If you intend to stay for several days, consider buying the rechargeable electronic plastic ticket: RD$200 which includes 7 journeys. You can then add single trips at RD$20, or buy an extra 10 journeys at RD$185, or an extra 20 journeys at RD$360. All tickets are sold at the Metro stations.
The new Metro is nice, very fast, air conditioned, and recommended for those travelling to places in the vicinity of the existing stations.
Taxis in Santo Domingo do not have meters. Therefore, you should check first with the hotel the approximate cost of any journey, and then confirm it with the driver before leaving. You should pay according to a set price of location to location. If the driver is unsure (or pretends to be...), ask him to call his dispatch office for confirmation. Waiting time is negotiated, and if you want to keep one driver all day, it might cost around US$25 on top of the cumulative cost of the completed trips. A taxi across town should be more or less RD$200 or US$5. Local expatriates recommend and use the Apolo taxi company: Apolo Taxi (809-537-7771). They should quote the fare when you call.
If you have a portable GPS use it and make sure the driver sees it; that might discourage him from taking the usual tourist detours...
Recently, TUV SUD entered the executive niche of the market (see image above) with a large fleet of brand new, air-conditioned taxis offering an uniformed driver, passenger insurance, and even a bottle of water.... It offers a free app, with which to call a taxi at the pressing of a button. It allows satellite positioning to locate the client. Besides, unlike Uber, you can call a taxi by phone: 809-561-3333, or flag it down in the street. You can find them also waiting outside most shopping malls. The minimum charge is RD$180 (US$4). There is a 20% discount if the app is used to call the car. The fare can be paid by credit card.
Uber has also entered the market, but like in many other cities around the world, it has difficulties with the licensing authorities and with the regular taxis. The US Embassy has warned its citizens about threats by transport trade unions against Uber that could result in sudden disruption of the service, or even in violence. Their tariffs are: RD$10 per kilometer + RD$5 per minute, with a minimum of RD$70, but consider the risks before you use them!