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Wisconsin DOT asked for assistance in analyzing variations of a previously designed and tested road closure gate.  The gate system was tested at TTI and is reported in TRR 1528 article titled "Wyoming Road Closure Gate."  The luminaire pole used to support the gate arm was equipped with a four bolt slip base design and an 8-ft long mast arm (with light) at the top.  The article stresses the importance of a high center of gravity and large mass moment of inertia to prevent the pole / gate system from crushing the top of the vehicle after impact.

Wisconsin wanted to use a variation of this closure gate system in future projects.  Some of these variations are listed below:

•          Eliminate the light / mast from the top of the pole
•          Replace the slip bolt base with another breakaway mechanism
•          Adding an electric powered winch to operate the gate
•          Addition of solar panels near top
•          Addition of control cabinet / battery near base

Alterations would only be allowable if the C.G. height and the mass moment of inertia values met or exceeded the values of the tested system.  MwRSF was asked to analyze multiple different luminaire pole types and sizes along with various attachments to the pole for this comparison. 

The last design that came from Wisconsin DOT is attached in PDF form.  It incorporates a slightly larger pole, solar panel, control cabinet, and a steel collar near the top to replace the light.  However, in order to satisfy the C.G. height requirement the weight of the collar must be increased from 83 pounds (as shown) to 141 pounds. The mass moment of inertia is satisfactory.  More details are available upon request.

The additional weight of the collar brings the total weight of the pole / gate system to 750 pounds.  The originally tested pole had a weight of 543 pounds.  This corresponds to a 38% increase in weight.  Now, the ORD and OIV values from the tests were low, so it is unlikely that the increased weight will cause detrimental decelerations to the vehicle.  Also, the solar panel is mounted high enough that it should fall behind the vehicle when impacted and not cause and damage to the occupant compartment.

The breakaway mechanism at the base of the pole was also being changed.  The behavior of the pole/gate may be significantly altered after changing the breakaway mechanism and adding over 200 pounds. Wisconsin was going to run this new design by FHWA to see if the closure gate would still be approved with the different breakaway mechanism as well as the added components.