Routing API Developer's Guide

Alternative Routes

If requested, the service can provide any available alternative routes. Alternative routes are available for all modes of transport. However, alternative routing for public transport takes some extra factors into account, such as timetables and number of transfers. Timetable routing can provide accurate time information but estimated routing cannot. This means that alternative routes are defined differently for each type of public transport routing:

In estimated routing, possible alternative routes are:

  • Geometrically different from the original route
  • Via different transport types
  • Not significantly different from the original route in estimated time of arrival.

In timetable routing, possible alternative routes can be:

  • Scheduled at different times
  • Via different transport types
  • Geometrically different, if not significantly different from the original route in estimated time of arrival.
Note: As timetable information is highly dynamic, we cannot give any particular guarantees on the number of and contents of alternative routes.

Requesting Alternative Routes

To request multiple alternative routes in the response, set the alternatives request parameter to the number of additional routes that the service should return. For example, if you specify alternatives=3 in the request, the service can return up to 4 routes in the response: the original route and three alternatives. Note that the alternatives parameter specifies maximum number of additional routes returned. For any route, the service may or may not find admissible alternatives, so it is possible that even with several alternatives requested, the response will contain only one route.

Alternative Route Ordering

Public transport alternatives are ordered by estimated preference. Simply, if no alternatives are requested, the best possible route is returned. Public transport routing algorithms take into account several criteria for estimating preference of resulting alternatives. Among these:
  • Route departure and arrival time
  • Duration of the trip
  • Number of transfers (changes) involved
  • Amount of walking distance involved
  • User preferences (if specified in the request)

In addition to public transport alternatives, your request may result in a walking only route. This happens when walking is preferred to public transportation or walking makes a viable alternative.