Hi, You can try this:
"Dear All,
In order to regularize the vehicle movement and to ensure timely availability of vehicle it has been decided to introduce vehicle requisition permission slip which will be available with HR Department. Employees /Head of Dept who require vehicle for official purpose are required to submit the “Vehicle requisition Permission slip” duly authorized by their Head of Departments. The same will be considered subject to availability of vehicles.
All are requested to co-operate. "