JSONRPCのサービスをポーリングするときはこんな感じでどうだろうか．

pollService.js

function pollService(url, method, params, callback) {  
  var ajaxReq = null;
  var error = false;
  function refresh(url, method, params, callback) {
    var methodCall = {method : method, params : params};
    ajaxReq =  $.ajax({
        type : "POST", dataType : "json",
        url : url,
        data : JSON.stringify(methodCall),
        timeout : 3000,
        success : callback,
        error : function(XMLHttpRequest, textStatus, errorThrown){
          error = true;
          alert("エラーが発生しました．処理を停止します．");
        },
        complete: function(){
          ajaxReq = null;
          if(!error){
            setTimeout(function(){refresh(url, method, params, callback)}, 1000);
          }
        }
      });
  }
  setTimeout(function(){refresh(url, method, params, callback)}, 1000);
}



$(function() {
  var url = "http://localhost:8080/jsonrpc/services/TrafficSimulatorService";
  callService(url, "startSimulation", [],
    function(data, dataType) {
      var pid = data.result;
      console.log(pid);
      var params = [pid, 0];
      callService(url, "getRoadData", [pid, 0],
        function(data, dataType) {
          console.log(JSON.stringify(data));
          pollService(url, "getVehicleData", params,
            function (data, dataType) {
              params[1]+=1;
              console.log(JSON.stringify(data));
            });
        });
    });
});

function printOut(data, dataType) {
  $("#result").append(
      "<div>" + dataType + "<br>" + JSON.stringify(data.result) + "</div><hr>");
}

function callService(url, method, params, callback) {
  var methodCall = {method : method, params : params};
  $.ajax({
    type : "POST", dataType : "json",
    url : url,
    data : JSON.stringify(methodCall),
    timeout : 3000,
    success : callback
  });
}