<div class="target">
 <div class="progress">
  <div class="progress-bar" role="progressbar" aria-valuenow="60" aria-valuemin="0" aria-valuemax="100">
   <span class="sr-only">60% Complete</span>
  </div>
 </div>
</div>

var target = $('.target').offset().top + 1;

$(document).scroll(function(){
  if( $(this).scrollTop() > target ){
   $('.progress-bar').animate({
     'width':'50%'
   });
  }
});