I think this block can be re-written as:
```
var closest = {'delta': 24, 'zone': null};
_.each(railsOffSets, function(zone, offset) {
    var delta = Math.abs(offset - userOffset);
    if (delta < closest.delta) {
        closest = {
            'delta': delta,
            'zone': zone
         };
    }
});
```
return closest.zone;