5. Transit accessibility – Service area

This section explains the Transit accessibility → Service Area maps part of the Accessibility Calculator menu (Figure 1).

Figure 1. Transit accessibility → Service Area maps menu

We present in detail the From locations – Fixed-time departure option and, then, the differences for each of the three other options.

5.1. The necessary datasets

Transit routing database, see Construct Databases → Transit routing database
The layer of buildings opened in the current QGIS project.

5.2. From service locations, fixed-time departure

Choose Transit accessibility → Service area maps → From service locations – fixed-time departure. Enter the parameters (Figure 2).

Figure 2. Service area maps → From service locations – Fixed-time departure dialog

Enter the necessary parameters: Transit routing database folder — the folder of the transit routing database. Must contain files stops.pkl, stoptimes.pkl, transfers_dict.pkl, idx_by_route_stop.pkl, routes_by_stop.pkl
Output folder — the folder for storing the results of the computation.
Output alias — the alias for the files of results and layers of visualization.
Layer of facilities — the layer of the facility buildings, may be selection set.
id — the name of the field with the unique building identifier, in the layer of buildings.
Visualization layer — the layer that will be used for visualization of accessibility maps, must be a part of the current QGIS project.
id — the name of the unique identifier field of the visualization layer unit. The features’ identifiers must be the subset of buildings’ identifiers. More information here.
Minimum number of transfers — minimum number of transfers of the transit trip, typically 0.
Maximum number of transfers — maximum number of transfers of the transit trip, typically 1 or 2.
Maximum walk distance to the initial PT stop, m — maximum acceptable walking distance between the trip origin and the first bus stop. The default value is 400 m.
Maximum walk distance at the transfer, m — maximum acceptable walking distance between two stops at the transfer.The default value is 150 m.
Maximum walk distance from the last PT stop, m — maximum acceptable walking distance between the last stop of a trip to the destination. The default value is 400 m.
Start at (hh:mm:ss) — trip start time.
Walking speed (km/h) — walking speed.
Maximal waiting time at the initial stop, min — maximum waiting time at the initial stop of the trip.
Maximal waiting time at the transfer stop, min — maximum waiting time at the transfer stop.
Boarding time gap — the minimum time previous activity, like arriving at the stop, and boarding the bus. Usually, zero or several seconds.
Maximal time travel, min — maximum total trip time.

Click Run to start. The Progressbar shows the progress of the computations. You can break the process of the computations by pressing Break. See the Log tab for the metadata about the computation run. The results of the computations are stored as two CSV report files in the Output folder. The first depicts the service area and contains all buildings that can be reached from at least one of the facilities in Maximal time travel, min or faster. Each of these accessible buildings is represented by the record that contains the id of the facility that served it at a minimal time, and all details of the trip between the facility and the building. The service area is visualized based on the Visualization layer. For the example of Service area maps → From service locations – Fixed-time departure computations and maps for the road network and buildings layer of TAMA see section 10.3. The service area file does not contain information on whether the building can be served by more than one facility. This information can be retrieved from the second output file, where for each facility, all buildings that can be served by this facility are listed. This second file can be used for deeper analysis of the accessibility, for example for recognizing buildings that can be reached from half or more of the facilities. In both output files, the details of every leg for every trip are described in detail, see the next section.

5.2.1. Service area computations - the log file and the structure of the report

The log file (Figure 3) in the results folder stores all settings of the run and the computation time .

Figure 3. Log file of the From service locations – fixed-time departure computations

The From service locations – fixed-time departure computations report contains all the details of each trip. Its structure is as follows (Figure 4):

Attribute	Meaning
Origin_ID	The ID of the facility building
Start_time	Time of the trip start
Walk_time₁	Time of walking to the initial stop
BStop_ID₁	The ID of the inital stop
Wait_time₁	Waiting time for a bus at the initial stop
Bus_start_time₁	Start time of the first leg of a trip
Line_ID₁	ID of the line used for the first leg of a trip
Ride_time₁	Duration of the first leg of a trip
AStop_ID₁	Alighting stop of the first leg of a trip
Bus_finish_time₁	Finish time of the first leg of a trip
Walk_time₂	Walking time to the first transfer stop
BStop_ID₂	ID of the first transfer stop
Wait_time₂	Waiting time for a bus at the first transfer stop
…Next legs and transfers	…If more transfers are performed
DestWalk_time	Walking time to a destination building
Destination_ID	The ID of the destination building
Destination_time	Time of arrival to destination
Duration	Total trip duration

Figure 4. The structure of the From service locations – fixed-time departure option output.

The example of the Transit accessibility → Service area → From service locations – fixed-time departure computations see here.

5.3. To service locations, fixed-time arrival

Run Transit accessibility → To service locations – fixed-time arrival option. Most of the parameters of the to-accessibility computations are the same as for the from-accessibility. This regards walking distance, walking speed, waiting time at stops, number of transfers, and the gap between sequential activities. The major difference is in establishing facilities and buildings to serve: For to-accessibility, facilities are destinations and not origins, as in the case of the from-accessibility (Figure 5).

Figure 5. The Facilities/Origins part of the To service locations - fixed time arrival dialog

In addition, the trip’s start time is substituted by the arrival time (Figure 6).

Figure 6. The Start/Arrival time part of the To service locations - fixed time arrival dialog

The Log and Result files for the to-accessibility are the same as for the from-accessibility, with minor differences that reflect the from-accessibility to the to-accessibility changes. The output table includes an additional attribute: “Latest time at destination”, that contains Arrives before time. The example of the Transit accessibility → Service area maps→ To service locations – fixed-time departure computations see here.

5.4. Service area for schedule-based departure or arrival

The modern users of public transport are aware of the time the bus arrives at the stop they plan to start from or at the final stop of the trip. These travelers start their trip and walk to the initial stop to be there just before the bus arrival or and choose take the bus that allows them to arrives at the destination just before they time a traveler must be thereat their destination. We have modified the RAPTOR algorithm to compute accessibility for these schedule-informed travelers. As an example of the “from” schedule-dependent accessibility computation, let us consider three travelers who reside in the same building, are willing to start their PT trip to work between 8:00 and 8:30, and travel up to 45 minutes. Let us also assume that there is one stop reachable by foot near their home in a 3-minute walk, and the first bus of each of the three lines that these travelers use for their trip to work arrive at this stop at 8:10, 8:15, and 8:25. In case of a fixed time start, all three travelers will start at 8:00, wait for their bus, and get with the PT whenever possible, probably making transfers, in 45 minutes. All trips will finish at 8:45 or earlier. In the case of schedule-dependent start, travelers will start their trips at 8:07, 8:12, and 8:22 (but not later than 8:30) and, after the 3-minute walk to a stop, will still have 42 minutes of travel time ahead. The trip that starts with the first bus must end at 8:07 + 0:45 = 8:52, with the second bus at 8:57, and with the third bus at 9:07. Since the time before the start of the trip is not included in the total travel time, the schedule-dependent accessibility will be always the same or higher than the accessibility computed for the fixed start time. Note that, instead of one start time parameter, 8:00 in this example, the forward schedule-dependent accessibility demands two – the “earliest start time” that remains 8:00, and the “maximum delay at start” that is 30 minutes. To repeat, the time between the earliest start time and the actual start of the trip is not included in the travel time. In the case of the to-accessibility computations, the latest arrival time is also substituted by the arrival interval. A traveler is allowed to arrive at the destination between the “earliest arrival time” and this time plus the “maximum lateness”. As above, the time between the actual arrival and the latest possible arrival that is equal to the “earliest arrival time” plus the “maximum lateness” is not included in the travel time. We consider the difference between the accessibility computations for travelers behaving according to the fixed time start or finish of the trip, and for the travelers whose behavior is schedule-defined as conceptual and will be happy to know your experience in employing these two approaches and comparing the results. The parameters of the From locations – schedule-based departure computations are almost the same as for the fixed-time option. The difference is in the description of the start of the trip which is defined by two parameters

The earliest start time — the earliest start time of a trip,

and the length of the period during which the trip can start:

Maximum delay at start, min — the maximum delay of the start of a trip.

For the To locations – schedule-based arrival accessibility, the description of arrival to the destination is defined by:

The earliest arrival time — the time of the earliest arrival to a destination,

and the maximum length of the arrival period:

Maximum lateness at arrival, min — the maximum lateness in arriving at a destination.

The examples of schedule-based accessibility are here.

The example section 10 contains the comparison between the estimates of the time-fixed and schedule-dependent accessibility.