Interchanges

Interchanges may be specified by detailed walks between pairs of stops or a network of routes pedestrians can use between the stops in a stop area (a cluster or group of stops). Another approach is to specify a minimum interchange time for the stops in a stop area that will include the walking and waiting time required to make connections between any of the stops. If these stop areas become too big then the minimum interchange time needed to get between the stops furthest apart will be much longer than will be required between stops in the centre of the area.

The fastest end to end journey times will be found if every point is available as a potential interchange. However this may not be the best for the passenger as some points on a network are much more suitable for interchange than others. They may have shelter and facilities and be a safer place to wait. Skill and knowledge of the network are required to get the balance right.

Some systems allow interchanges to be ranked in order of preference. This is particularly useful where interchange is required between two routes that share a number of stops or stations along their routes. The end to end journey time would be the same whichever stop was used to interchange but the ranking of the interchanges ensures that the system selects the most suitable location.

Another way to achieve the same effect is to adjust the minimum interchange time for an interchange. If this is increased at some stops then interchange will usually be quicker if alternative nearby stops are used.

Minimum Interchange Times

In most systems these can be set for each stop or group of stops. Individual systems use these values in different ways.

When exported via ATCO CIF the records can take the form of:

Location Interchange - minimum time to interchange between two points to include waiting
Cluster Interchange - minimum recommended interchange time within cluster
Cluster Walk Links - minimum travel time from origin cluster to destination cluster

Within ATCO CIF an interchange can only occur if a stop is part of a cluster. Therefore for interchange at a single stop, a cluster of 1 must be created!

The values will normally be created by the local authority in consultation with the public transport operators. Sometimes blanket values are used. 7 minutes is a popular one in a rural county. But 7 minutes will be too high if buses are timed to connect with just a 5 minute interval. Therefore sometimes it will be appropriate to have a lower value. However if services are unreliable, perhaps through traffic congestion, then a higher value will be appropriate.

Some systems allow guaranteed connections to be specified. In ATCO CIF these are defined by Journey Association records and allow two journeys to be listed as connecting at a particular point on certain days of the week between certain dates. Journeys identified in this way may permit interchange at less than the Minimum Interchange time.

Ideally an interchange time should be directional and some systems reflect this by having an added number of minutes to an interchange between specific modes. The frequency of the next leg of the journey and whether it is the last service of the day would be good determinants of how much time a passenger would like to have for interchange.

The rail industry has agreed interchange times to be used when interchanging between trains at rail stations. These are included in the rail data which is supplied each week by ATOC to all of the datacentres producing traveline data.

Interchange related errors

Missing interchange - an expected interchange is not available in the data which causes either a journey by a longer route or a even a failure to find a journey solution at all.
Minimum interchange value too high - a connection is not allowed because it is less than the minimum interchnge time.
Wormholes - two points which are far apart erroneously have the same identity number or coordinates. The journey planner will find the speed of light journey between them and offer this as a solution, possibly to many journeys, because of the time saving.

Knowledgebase of Facilities at Interchanges

Passengers may need to know what facilities are available at a point that they are asked to interchange. The name eg Bus Station, will give an expectation of shelter and information. More work needs to be done to provide more information about facilities, not least to meet the requirements of the Disability Dicriminiary Act.

Go to the Knowledgebase.