Javascript library that offer some usefull function when you work 
with path/directions/routes in Google Maps API, under LGPL Licence.

// Simply create a point on Paris and Zurich centers
var paris = new google.maps.LatLng(48.856667,2.350987);
var zurich = new google.maps.LatLng(47.369024,8.538033);

// Now retrieve a Bounds object that surround all paris.
// ie a square of 10km with $paris as center
var parisRectangle = paris.getRadialBoundaries(5);

// Simply get the straight distance between Paris and Zurich, result in kilometers
// Something around 490km
var paris_zurich_distance = paris.distanceFrom(zurich);

// Then, retrieve the point at 140km between Paris->Zurich (on a straight line)
// Again, distance is in kilometers
// This point is near "Troyes" french city.
var somewhereNearTroyes = paris.pointBetween(zurich,140);

// Retrieve the route from Paris to Zurich
var request = {
  origin: paris,
  destination: zurich,
  travelMode: google.maps.DirectionsTravelMode.DRIVING
};
directionsService.route(request, function(response, status) {
  if (status != google.maps.DirectionsStatus.OK) return;
  var leg = response.routes[0].legs[0];
  
  // Once we get that result, compute the point at one hour on the road from Paris to Zurich :)
  var oneHoursFromParisOnTheRoadToZurich = getDirectionPointAtDuration(leg,1*60*60);
  
  // Or the point at the middle of the trip
  // Not the middle in term of kilometer, but in times!
  var middleInTimeFromParisOnTheRoadToZurich = getDirectionPointAtDuration(leg,leg.duration.value/2);
  
});