var m = L.map('map').setView([42.2, -71], 8),
mapQuestAttr = 'Tiles Courtesy of <a href="http://www.mapquest.com/">MapQuest</a> &mdash; ',
osmDataAttr = 'Map data &copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors',
mopt = {
    url: 'http://otile{s}.mqcdn.com/tiles/1.0.0/osm/{z}/{x}/{y}.jpeg',
    options: {attribution:mapQuestAttr + osmDataAttr, subdomains:'1234'}
 };
var mq=L.tileLayer(mopt.url,mopt.options).addTo(m);
var roads = L.geoJson.ajax("roads.json",{style:{opacity:0,fillOpacity:0}}).addTo(m);