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You must have a CERN Driving License to use the car. Go to EDH, click "Other Tasks" and "Car Driving Authorisation", fill out the form, submit it and wait for notification it has been approved. The notification includes information on getting your own plastic gadget to silence the alarm. As this might expire quietly without warning, it is worth checking the license validity before you go to CERN. Its status can be found in ADaMS under "training & permits".
Note that the CERN Driving License does not allow you to drive off-site such as going to the SLAC apartment; you will also need a Mission Order to do so. Go to EDH, click "Other Tasks" and then "Mission Order". Mission Orders have to be renewed every calendar year. (Edit by AndyS: I tried to request Mission Order for travel St-Genis-Poilly and Prevessin and it was refused, both locations are considered inside CERN perimeter so Mission Order is not required for them. To see the map of CERN perimeter see last page of "Operational Circular No. 04", also linked from https://admin-eguide.web.cern.ch/en/procedure/official-vehicles)
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