In 1971 J. Standard Baker Quoted " Drivers Towing Trailers  Are Four (4) Times As Unsafe As Those In Cars Alone! 

The United States Has Never Issued Any Direction Or Laws Like This.
  If a tester or a vehicle inspector believes that a vehicle is unroadworthy, the tester or vehicle inspector must record that the vehicle is unroadworthy on the copy of the inspection certificate to be returned to the Department and must affix a rejection sticker to that copy of the inspection certificate.

(5)All of the following parts of a Type 1 trailer must be inspected:

                (a)    for a trailer, brakes, if any;

                (b)    coupling devices and towing connections;

                (c)    suspension system;

                (d)    tires and wheels;

                (e)    frame;

                (f)    body components.

As noted at the Animal Transportation Association Vancouver 2012 international conference on horse transport, the lack of standards in the manufacture of non-commercial horse trailers contributes to injury and death of horses and humans. Your USRider on-going study of over 800 known trailer incidents reveals poor quality materials including tires, wiring, braking performance, instability at highway speeds, poor welds, trailer skin so thin it can be punched through with a fist, shifting loads, mismatch between trailer and tow vehicle, tow vehicle and trailer separation, overloading, no mandatory recall on defective parts, and horses thrown or falling from the trailer and posing an additional road hazard. As well, few trailers meet the Five Freedoms endorsed by animal welfare interests: providing an environment conducive to normal behavior, rest, drinking and eating, and which minimizes the risk of injury, mental or physical distress, or disease. Currently, there are no standards in North America for manufacturing horse trailers. To the best of my knowledge, standards are also non-existent in New Zealand, Australia, and Europe.

No Inspections, No Safety Standards On All Utility Trailers Under 3,000 GVWR!

The Problem And The Facts