There are research projects about this in various countries. Japan has made great achievements in robotics. But I did not find a present implementation in Japan. 1) "The driverless car concept embraces an emerging family of highly automated cognitive and control technologies, ultimately aimed at a full "taxi-like" experience for car users, but without a human driver. Together with alternative propulsion, it is seen by some as the main technological advance in car technology by 2020. Driverless passenger programs include the 800 million ECU EUREKA Prometheus Project on autonomous vehicles (1987-1995), the 2getthere passenger vehicles (using the FROG-navigation technology) from the Netherlands, the ARGO research project from Italy, and the DARPA Grand Challenge from the USA. For the wider application of artificial intelligence to automobiles see smart cars." Source and further information: http://en.wikipedia.org/wiki/Driverless_car 2) "According to ICT Results, a EU-funded project named Embounded 'has achieved the twin, and apparently contradictory goals, of making embedded systems both smarter and tougher.' One example is the robuCAB, a '4 seats automated people mover' developed by a French company and built from a 4 wheel-drive electric chassis with on-board PC. This autonomous vehicle follows the kerb and carries several embedded systems, with one camera on the path edge, another device tracking the angle and direction of the kerb, while others control the gearing and acceleration. robuCABs are not totally independent. They move over pre-defined circuits which contain a series of sensors below the ground." Source and further information: http://www.primidi.com/2008/03/12.html Further information: http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=1512 3) "Robot Taxis for Europe: The EU will address the problem of personal vehicles by launching their CityMobil project. CityMobil is a The €40 million project involving 28 partners in 10 countries. They will construct and operate three operating robot transportation systems - London's Heathrow airport, the new exhibition centre in Rome and the town of Castellón in eastern Spain. The systems will operate on-demand like taxis but will not have drivers. The idea is that this type of public transportation will be a middle ground between the restrictions of mass transit and the excesses of individual cars. They are designed to operate within existing roads and infrastructue. The pupose of the CityMobil projects will be to find the obstacles to full-scale implementation of driverless systems. Other projects will also be proposed as opportunities arise. The idea of robot taxis is not brand new for Europe. CityMobil is an expansion of the CyberMove and Cybercars projects that date back to 2001." Source and further information: http://robotgossip.blogspot.com/2006_09_01_archive.html 4) "If you happen to stop over at Kita Kyushu airport in the southwest of Japan this month, don’t be surprised if the porter offering to carry your bags is a four-foot green chap with an oddly metallic voice. RoboPorter is currently being tested at the regional airport by Yaskawa Electric for a few hours each afternoon. As you’ll see from the photo gallery over at Japanese site Robot Watch, the machine looks something like a tiny flatbed truck and includes a screen that serves as its human face. Operation is pretty simple – a would-be user simply approaches the robot and tells it orally where to take the bag he’s just handed over. There’s a touch-screen with a map of the facilities as an alternative. The machine can handle up to 50kg of luggage per trip and can also dispense information about the airport. As the range of destinations is limited to the bus stops or taxi ranks, it’s clear this is a work in progress but at least RoboPorter isn’t going to hustle arriving tourists for tips or send them to its pal’s taxi for a ‘special’ fare into town." Source and further information: http://www.digitalworldtokyo.com/index.php/digital_tokyo/articles/airport_porter_revealed_as_bag_fondling_robot/ 5) "Robot Control with Biological Cells": http://eprints.ecs.soton.ac.uk/11294/1/TsudaS05RobotCtrlCellPreProc.pdf

No, there are no robotic taxis in Japan as of today. (Although I've ridden in a couple of taxis where the driver was as stoic as a robot.)