Auto Parts: speed governors for cars, speed governors, antique steam

Question
How long have governor's been placed on vehicles- such as school buses or on private cars as an after market accessory?

Answer
    Governors go back a lot further than cars or buses.  Those spinning balls you see on antique steam engines are the governor.  Governors have been used on commercial vehicles since the very beginning.  They are not generally available as an aftermarket accessory, however.  Gasoline engines, such as the big IH trucks and school buses I drove in the '70's, used a carburetor with a throttle stop that was hooked to the oil pressure in the engine.  When the pressure rose above a certain value (oil pressure is directly dependent on engine RPM) it kept the throttle from opening any further.  This was sometimes also regulated by a valve in the distributor body, giving a finer control over the engine speed.  Adding this feature to a vehicle that did not come with it would mean replacing the carburetor with one that had a governor built-in.  Holley did sell these at one time.  All non-electronic diesels have a governor that is part of the injection pump mechanism.  It's simply a matter of calibrating it to a certain engine speed.  Remember, the real reason for these governors wasn't to keep the speed of vehicle down, it was to reduce wear on the engine.  Commercial operators don't care how fast their employees drive; faster gets the job done quicker and traffic tickets must be paid by the driver, not the owner.  But they do care about how much it costs to operate the rig, including maintenance, and a governor keeps that cost down.
    Nowadays a clever programmer with the appropriate equipment can go into the OBDII ECM and set a governing vehicle or engine speed, either or both.  The equipment needed to do this is expensive, and the know-how hard to come by.  Still, if you want to keep your kid from abusing his privileges or you want to use cheaper tires with a lower speed rating, it might be worth the trouble.