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Calculate travel time and monetary cost Pareto frontier

Source: R/pareto_frontier.R
pareto_frontier.Rd

Fast computation of travel time and monetary cost Pareto frontier between origin and destination pairs.

Usage

pareto_frontier(
  r5r_network,
  origins,
  destinations,
  mode = c("WALK", "TRANSIT"),
  mode_egress = "WALK",
  departure_datetime = Sys.time(),
  time_window = 10L,
  percentiles = 50L,
  max_walk_time = Inf,
  max_bike_time = Inf,
  max_car_time = Inf,
  max_trip_duration = 120L,
  fare_structure,
  fare_cutoffs,
  walk_speed = 3.6,
  bike_speed = 12,
  max_rides = 3,
  max_lts = 2,
  n_threads = Inf,
  verbose = FALSE,
  progress = FALSE,
  output_dir = NULL,
  r5r_core = deprecated()
)

Arguments

r5r_network

A routable transport network created with build_network().

origins, destinations

Either a POINT sf object with WGS84 CRS, or a data.frame containing the columns id, lon and lat.

mode

A character vector. The transport modes allowed for access, transfer and vehicle legs of the trips. Defaults to WALK. See details for other options.

mode_egress

A character vector. The transport mode used after egress from the last public transport. It can be either WALK, BICYCLE or CAR. Defaults to WALK. Ignored when public transport is not used.

departure_datetime

A POSIXct object. Only affects public transport legs; when routing with public transport, it must fall within the service period of the GTFS feeds (calendar.txt; see check_transit_availability()). Defaults to Sys.time(). See details for how datetimes are parsed.

time_window

An integer. The time window in minutes. Departures are simulated every minute from departure_datetime until time_window minutes later, and travel times are summarized over these departures using percentiles (the median by default). Defaults to 10. See vignette("time_window", package = "r5r").

percentiles

An integer vector (max length of 5). Specifies the percentile to use when returning travel time estimates within the given time window. This parameter is applied to the travel time estimates only (e.g. if the 25th percentile is specified, and the output between A and B is 15 minutes and 10 dollars, 25% of all trips cheaper than 10 dollars taken between these points are shorter than 15 minutes). Defaults to 50, returning the median travel time. If a vector with length bigger than 1 is passed, the output contains an additional column that specifies the percentile of each travel time and monetary cost combination. Due to upstream restrictions, only 5 percentiles can be specified at a time. See the R5 documentation at https://docs.conveyal.com/analysis/methodology#accounting-for-variability.

max_walk_time

An integer. The maximum walking time (in minutes) to access and egress the transit network, make transfers, or complete walk-only trips. Applies to each leg separately (e.g. 15 allows up to 15 minutes to reach transit and another 15 after leaving it). Defaults to Inf (no limit besides max_trip_duration). In walk-only trips, the lower of max_walk_time and max_trip_duration applies.

max_bike_time

An integer. The maximum cycling time (in minutes) to access and egress the transit network, make transfers, or complete bicycle-only trips. Applies to each leg separately (e.g. 15 allows up to 15 minutes to reach transit and another 15 after leaving it). Defaults to Inf (no limit besides max_trip_duration). In bicycle-only trips, the lower of max_bike_time and max_trip_duration applies.

max_car_time

An integer. The maximum driving time (in minutes) to access and egress the transit network, or to complete car-only trips. Applies to each leg separately (e.g. 15 allows up to 15 minutes to reach transit and another 15 after leaving it). Defaults to Inf (no limit besides max_trip_duration). In car-only trips, the lower of max_car_time and max_trip_duration applies.

max_trip_duration

An integer. The maximum trip duration in minutes. Defaults to 120.

fare_structure

A fare structure object, following the convention set in setup_fare_structure(). This object describes how transit fares should be calculated. See vignette("fare_structure", package = "r5r") for its structure. Required: without it there are no fares to trade off against travel time.

fare_cutoffs

A numeric vector, required. The monetary cutoffs (each greater than or equal to 0) used to build the Pareto frontier. Usually these are all possible fares in your fare_structure, including sums of fares for trips with transfers. Coarse cutoffs merge different trips: with routes costing $3 and $4 and a single cutoff of 5, the output shows the fastest trips costing up to $5 but not which route they used; c(3, 4) separates them.

walk_speed

A numeric. Average walk speed in km/h. Defaults to 3.6.

bike_speed

A numeric. Average cycling speed in km/h. Defaults to 12.

max_rides

An integer. The maximum number of public transport rides allowed in the same trip. Defaults to 3.

max_lts

An integer between 1 and 4. The maximum level of traffic stress that cyclists will tolerate. A value of 1 means cyclists will only travel through the quietest streets, while a value of 4 indicates cyclists can travel through any road. Defaults to 2. See details.

n_threads

An integer. The number of threads to use when running the router in parallel. Defaults to Inf (all available threads).

verbose

A logical. Whether to show R5 informative messages when running the function. Defaults to FALSE (R5 error messages are still shown). TRUE shows detailed output, useful for debugging issues not caught by r5r.

progress

A logical. Whether to show a progress counter when running the router. Defaults to FALSE. Only works when verbose is FALSE. May slightly slow computation, as the counter is synchronized across threads.

output_dir

Either NULL (the default) or a path to an existing directory. When a path is given, the function writes the results as .csv files to that directory and returns the path instead of the results. Useful in memory-constrained settings, as results are not loaded into RAM. Missing values (NA) are written as empty fields.

r5r_core

The r5r_core argument is deprecated as of r5r v2.3.0. Use the r5r_network argument instead.

Value

A data.table with the travel time and monetary cost Pareto frontier between the specified origins and destinations. An additional column identifying the travel time percentile is present if more than one value was passed to percentiles. Origin and destination pairs whose trips couldn't be completed within the maximum travel time using less money than the specified monetary cutoffs are not returned in the data.table. If output_dir is not NULL, the function returns the path specified in that parameter, in which the .csv files containing the results are saved.

Transport modes

R5 allows for multiple combinations of transport modes. The options include:

  • Transit modes: TRAM, SUBWAY, RAIL, BUS, FERRY, CABLE_CAR, GONDOLA, FUNICULAR. The option TRANSIT automatically considers all public transport modes available.

  • Non transit modes: WALK, BICYCLE, CAR.

Level of Traffic Stress (LTS)

When cycling is enabled in R5 (by passing the value BICYCLE to either mode or mode_egress), setting max_lts will allow cycling only on streets with a given level of danger/stress. Setting max_lts to 1, for example, will allow cycling only on separated bicycle infrastructure or low-traffic streets and routing will revert to walking when traversing any links with LTS exceeding 1. Setting max_lts to 3 will allow cycling on links with LTS 1, 2 or 3. Routing also reverts to walking if the street segment is tagged as non-bikable in OSM (e.g. a staircase), independently of the specified max LTS.

The default methodology for assigning LTS values to network edges is based on commonly tagged attributes of OSM ways. See more info about LTS in the original documentation of R5 from Conveyal at https://docs.conveyal.com/learn-more/traffic-stress. In summary:

  • LTS 1: Tolerable for children. This includes low-speed, low-volume streets, as well as those with separated bicycle facilities (such as parking-protected lanes or cycle tracks).

  • LTS 2: Tolerable for the mainstream adult population. This includes streets where cyclists have dedicated lanes and only have to interact with traffic at formal crossing.

  • LTS 3: Tolerable for "enthused and confident" cyclists. This includes streets which may involve close proximity to moderate- or high-speed vehicular traffic.

  • LTS 4: Tolerable only for "strong and fearless" cyclists. This includes streets where cyclists are required to mix with moderate- to high-speed vehicular traffic.

For advanced users, you can provide custom LTS values by adding a tag <key = "lts"> to the osm.pbf file.

Datetime parsing

r5r ignores the timezone attribute of datetime objects when parsing dates and times, using the study area's timezone instead. For example, let's say you are running some calculations using Rio de Janeiro, Brazil, as your study area. The datetime as.POSIXct("13-05-2019 14:00:00", format = "%d-%m-%Y %H:%M:%S") will be parsed as May 13th, 2019, 14:00h in Rio's local time, as expected. But as.POSIXct("13-05-2019 14:00:00", format = "%d-%m-%Y %H:%M:%S", tz = "Europe/Paris") will also be parsed as the exact same date and time in Rio's local time, perhaps surprisingly, ignoring the timezone attribute.

Routing algorithm

The detailed_itineraries() and pareto_frontier() functions use an R5-specific extension to the McRAPTOR routing algorithm. The implementation used in detailed_itineraries() allows the router to find paths that are optimal and less than optimal in terms of travel time, with some heuristics around multiple access modes, riding the same patterns, etc. The specific extension to McRAPTOR to do suboptimal path routing is not documented yet, but a detailed description of base McRAPTOR can be found in Delling et al (2015). The implementation used in pareto_frontier(), on the other hand, returns only the fastest trip within a given monetary cutoff, ignoring slower trips that cost the same. A detailed discussion on the algorithm can be found in Conway and Stewart (2019).

  • Delling, D., Pajor, T., & Werneck, R. F. (2015). Round-based public transit routing. Transportation Science, 49(3), 591-604. doi:10.1287/trsc.2014.0534

  • Conway, M. W., & Stewart, A. F. (2019). Getting Charlie off the MTA: a multiobjective optimization method to account for cost constraints in public transit accessibility metrics. International Journal of Geographical Information Science, 33(9), 1759-1787. doi:10.1080/13658816.2019.1605075

See also

Other routing: arrival_travel_time_matrix(), detailed_itineraries(), expanded_travel_time_matrix(), travel_time_matrix()

Examples

library(r5r)

# build transport network
data_path <- system.file("extdata/poa", package = "r5r")
r5r_network <- build_network(data_path = data_path)
#> Using cached R5 version from /home/runner/.cache/R/r5r/r5_jar_v7.5.1/r5-v7.5-1-gf3631e9-all.jar
#> ℹ Using cached network from
#>   /home/runner/work/_temp/Library/r5r/extdata/poa/network.dat.

# load origin/destination points
points <- read.csv(file.path(data_path, "poa_hexgrid.csv"))[1:5,]

# load fare structure object
fare_structure_path <- system.file(
  "extdata/poa/fares/fares_poa.zip",
  package = "r5r"
)
fare_structure <- read_fare_structure(fare_structure_path)

departure_datetime <- as.POSIXct(
  "13-05-2019 14:00:00",
  format = "%d-%m-%Y %H:%M:%S"
)

pf <- pareto_frontier(
  r5r_network,
  origins = points,
  destinations = points,
  mode = c("WALK", "TRANSIT"),
  departure_datetime = departure_datetime,
  fare_structure = fare_structure,
  fare_cutoffs = c(4.5, 4.8, 9, 9.3, 9.6)
)
#> Loading required namespace: testthat
head(pf)
#>            from_id           to_id percentile travel_time monetary_cost
#>             <char>          <char>      <int>       <int>         <num>
#> 1: 89a901291abffff 89a901291abffff         50           2           4.5
#> 2: 89a901291abffff 89a9012a3cfffff         50          73           9.0
#> 3: 89a901291abffff 89a901295b7ffff         50          61           4.5
#> 4: 89a901291abffff 89a901295b7ffff         50          55           4.8
#> 5: 89a901291abffff 89a901295b7ffff         50          46           9.0
#> 6: 89a901291abffff 89a901284a3ffff         50          61           4.8

stop_r5(r5r_network)
#> r5r_network has been successfully stopped.