Perfect example why the Nei is so far behind the mainland, "Joey Manahan isn’t sure how DOT officials can prevent people from returning." 
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Joey's big mistake is looking inward for answers. Needs to look mainland where these problems have already been solved.
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Cities have had success in eliminating homeless around/under road structures by placing rip wrap, large boulders with sharp edges, up to the top of the overhead structure, randomly under the structure to take up space, prevent large homeless structures from being built.   http://voiceofoc.org/wp-content/uploads/2017/03/Nelson-riverbed-project-1-1170x659.jpg
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Cities have also installed large diameter steel poles, 6" or so, into concrete and going straight up to the top or side of the overhead road. 
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Also large diameter concrete piping, may be filled with concrete. 
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Both steel and concrete set too close together for anyone to squeeze through.  
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Ok Joe. Now you know what to do.