The trains are also able to be operated exclusively by computers, becoming one of the earliest installations of Standard Elektrik Lorenz's "SelTrac IS" system (now owned and delivered by Thales Rail Signalling Solutions), doing away with the need for a human operator. However, due to opposition from the transit workers' union and public perception, operators were retained; the union has firmly opposed driverless trains. (Other systems took full advantage of the automated operation and Vancouver's SkyTrain has been automated since 1985 without incident.) The Scarborough line trains have only one operator, unlike most of the other TTC subway lines, which carry both a guard at the rear, who operates the train's doors, and an operator, who drives the train from the front. (Line 4 Sheppard, however, has used a single operator only since October 2016.) In practice, the Scarborough line trains drive themselves; the operator monitors their operations and controls the doors. One feature, which was not implemented at the time of Scarborough line's opening, is the automated next stop announcement system, which was introduced in January 2008 (which means operators are no longer required to call out stops manually) and uses the voice-over of Susan Bigioni, a TTC employee, identical to those used on the T1 series and the retired H4, H5, and H6 trains.