Opção de rotas sugeridas na API do Google Maps?

Eu tenho um requisito para mostrar várias rotas entre a origem e o destino. Por exemplo: se eu estiver selecionando uma fonte e um destino, eu posso encontrar uma única rota. Mas, como no google maps, temos uma opção de rotas sugerida, a qual eu preciso implementar, mas falhei com todas as minhas tentativas. Por favor, encontrar o código abaixo (Working, por exemplo, que mostra a rota única entre uma fonte e um destino). Por favor, orientar se eu perdi alguma coisa. desde já, obrigado

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="initial-scale=1.0, user-scalable=no">
<meta charset="utf-8">
<title>Chart</title>
<style>
html,body,#map-canvas {
    height: 100%;
    margin: 0px;
    padding: 0px
}

#panel {
    position: absolute;
    top: 5px;
    left: 50%;
    margin-left: -180px;
    z-index: 5;
    background-color: #fff;
    padding: 5px;
    border: 1px solid #999;
}
</style>
<script
    src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false"></script>
<script> var directionsDisplay; var directionsService = new google.maps.DirectionsService(); var map;  
function initialize() 
{   
    directionsDisplay = new google.maps.DirectionsRenderer();   
    var delhi = new google.maps.LatLng(28.6168, 77.2434);  
     var mapOptions = 
         {     
             zoom: 6,     
             mapTypeId: google.maps.MapTypeId.ROADMAP,     
             center: delhi   
         }  
      map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);   
      directionsDisplay.setMap(map); }  function calcRoute() {  
      var start = document.getElementById('start').value;   
      var end = document.getElementById('end').value;  
       var waypts = [];   
       var checkboxArray = document.getElementById('waypoints');   
       for (var i = 0; i < checkboxArray.length; i++) 
           {     if (checkboxArray.options[i].selected == true) 
               {       
               waypts.push({           
               location:checkboxArray[i].value,           
               stopover:true});     
               }   
           }    
       var request = 
           {       
               origin: start,       
               destination: end,       
               waypoints: waypts,       
               optimizeWaypoints: true,       
               travelMode: google.maps.TravelMode.DRIVING   
            };   
        directionsService.route(request, function(response, status) 
                {     
                    if (status == google.maps.DirectionsStatus.OK) 
                        {       
                            directionsDisplay.setDirections(response);       
                            var route = response.routes[0];      
                            var summaryPanel = document.getElementById('directions_panel');       
                            summaryPanel.innerHTML = '';       // For each route, display summary information.      
                            for (var i = 0; i < route.legs.length; i++) 
                            {        
                                var routeSegment = i + 1;        
                                summaryPanel.innerHTML += '<b>Route Segment: ' + routeSegment + '</b><br>';        
                                summaryPanel.innerHTML += route.legs[i].start_address + ' to ';        
                                summaryPanel.innerHTML += route.legs[i].end_address + '<br>';         
                                summaryPanel.innerHTML += route.legs[i].distance.text + '<br><br>';      
                            }     
}   }); 
}  google.maps.event.addDomListener(window, 'load', initialize);      </script>
</head>
<body>
<div id="map-canvas" style="float: left; width: 70%; height: 100%;"></div>
<div id="control_panel"
    style="float: right; width: 30%; text-align: left; padding-top: 20px">
<div style="margin: 20px; border-width: 2px;"><b>Loco Journey Start Station:</b> <select
    id="start">
    <option value="Tughlakabad">Panvel</option>
    <option value="Lucknow">Lucknow</option>
    <option value="Firozpur">Firozpur</option>
    <option value="Ghaziabad">Ghaziabad</option>
</select> <br>
<b>Journey:</b> <br>
<i>(Ctrl-Click for multiple selection)</i> <br>
<select multiple id="waypoints">
    <option value="Bhopal">Bhopal</input>
    <option value="Raipur">Raipur</input>
    <option value="Farukkhabad">Farukkhabad</input>
    <option value="Jhansi">Jhansi</input>
</select> <br>
<b>Loco Journey End Station:</b> <select id="end">
    <option value="Lucknow">Lucknow</option>
    <option value="Firozpur">Firozpur</option>
    <option value="Ghaziabad">Ghaziabad</option>
    <option value="Tughlakabad">Tughlakabad</option>
</select> <br>
<input type="submit" onclick="calcRoute();"></div>
<div id="directions_panel"
    style="margin: 20px; background-color: #FFEE77;"></div>
</div>
</body>
</html>

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