An operational safety enhancement device, that enables the automatic operation of the day to day train business, is called Unattended Train Operation (UTO). In these days more and more cities change their subway, monorail and train handling to Unattended Train Operation systems, these includes cities like Delhi, London and Toronto .
Perhaps the biggest dream of a mobility service in smart cities is the automatic operation of the traffic. Though it is still a long way to go, for the public transport business it has already become real. Unattended Train Operation has been graded into 5 grades of automation in metro systems (see Figure 1). These range from the grade 0, which is the on-sight operation, to 4 the fully automatic handled train operation with no staff onboard this level is called the Unattended Train Operation (UTO) . Today most of the automated train systems satisfy the grade of automatization 2 or 3.
To achieve the Unattended Train Operation three main system have to be implemented:
- ATP – Automatic Train Protection
The Automatic Train Protection system manage the train’s basic safety behavior, like red lights, collision avoidance and make sure the train follows the speed limits.
- ATO – Automatic Train Operation
ATO systems enable a system to handle the essential driving functionalities. Still the door closure and the emergency handling has to be done by the train staff.
- ATC – Automatic Train Control
The last system regards the train rout, signal operations and the train regulations. ATC systems also maintain the train schedule.
Figure 1 – Grades of Automation 
For me the unattended train operation is a major step forward into a smart city. Especially in Germany the train service has enormous troubles to remain on schedule. How experiences in early adaptor cities like Nuremberg, New York City or the Vancouver Sky Train reveal enables a driverless train service to achieve high and consistent on-time reliability . Also the train service benefits through the unattended train operation in matter of safety, riding comfort, traceability of target velocity and energy saving .
Even though the new construction of UTO train systems have a low comparative weight in the overall budget, it is still a huge investment to adapt the system of UTO. To make it affordable, more effort has to be put in the conversion of old train lines.
 https://en.wikipedia.org/wiki/Automatic_train_operation#cite_note-1; 12.10,2015  http://www.uitp.org/sites/default/files/Metro%20automation%20-%20facts%20and%20figures.pdf; 12.10,2015  http://www.uic.org/cdrom/2006/wcrr2006/pdf/205.pdf; 12.10,2015  http://www.translink.ca/en/About-Us/Media/2011/October/Expo-Line-Upgrades-Improve-Communications.aspx; 12.10,2015  http://www.ics.esys.tsukuba.ac.jp/yasunobu/papers/ATO1985.pdf; 12.10,2015