// Load the dynamic json file for highways, etc.
    // Ref: https://codepen.io/KryptoniteDove/post/load-json-file-locally-using-pure-javascript
    function loadJSON(inFile, callback)
    {
        var xobj = new XMLHttpRequest();
        xobj.overrideMimeType("application/json");
        xobj.open('GET', inFile, true);
        xobj.onreadystatechange = function()
        {
            if (xobj.readyState == 4 && xobj.status == "200")
            {
                callback(xobj.responseText);
            }
        };
        // We want ajax to ignore any cached responses
        xobj.setRequestHeader('If-Modified-Since', 'Sat, 01 Jan 2000 01:01:01 GMT')
        xobj.send(null);
    }