Chattanooga Cell Phone External O-D Matrix Development

Transcription

1 Chattanooga Cell Phone External O-D Matrix Development Process and Findings Presented to Tennessee Model Users Group (TNMUG) November 10,

2 Background Chattanooga RPA/CHCNGA TPO wanted to update their external travel survey on minimal budget» Anonymous cell phone data increasingly available with algorithms becoming more refined for post processing» Possibility investigated for Origin-Destination matrix development» Cell phone data also used for speed determination but found to be less useful» Airsage, Inc. contracted to post process movement of cellular devices obtained from carriers

3 Overview Geographies used» External zones» Grid cells» Mega zones Data collection procedure Post processing Results and observations Conclusions

4 Chattanooga 2035 Model External Stations Model consists of 38 External Zones» Particularly interested in high volume external zones 800 (I-75 S) 813 (I-59) 814 (I-24) 829 (I-75 N)» These represent Interstate stations 4

5 Grid Cells Grid cells correspond to cellular phone tower coverage areas 900 grid cells used in study area Individual cells assigned to external stations (tried to isolate each external station in its own grid cell) Initial results unsatisfactory» Several major OD movements missing» Examples included: I-75 N to I-75 S I-59 S to I-75» Other movements very small: I-75 S to US 27 N I-24 to I-75 S 5

6 Megazones Low initial trip numbers led to use of Megazones 6

7 Megazone Concept Adjacent grid cells aggregated into megazones Increased capture rate Clarified major OD trip movements Three types of megazones 1 - External megazones (E#) outside model study boundary 2 - Internal megazones (I#) internal to model 3 - Station megazones (ST#) external stations 7

8 Megazone Concept (Cont d) E-E trips determined by sighting sequence» Phone sighted in E#, then ST#, then I#, then ST#, then E#, is a through trip» Some sequences not clear and thus omitted For hypothetical cellular device 123:» Sighting 1 is in external megazone E21» Sighting 2 is in station megazone ST12» Sighting 3 is in internal megazone I2» Sighting 4 is in station megazone ST24» Sighting 5 is in external megazone E12 8

9 Megazone Concept (Cont d) E 21 ST12 I 2 ST 24 E 12 Can confidently be stated that device 123 made an E-E trip For hypothetical mobile device 678, Sighting 1 is seen in external megazone E21 E21 E7» Sighting 2 is seen in external megazone E7» In this case external-to-external trip through study area cannot be confirmed» No sighting observed in an internal megazone» Trip may have used a path external to study area 9

10 Megazone Lookup Table Note the aggregated matches Table used in matrix post processing for TransCAD import requirements Grid Cell ID External Station ID Megazone (Model) 830 ST ST ST ST ST ST13_A ST ST ST ST ST17_A ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST5_A ST ST ST7_A ST ST ST ST ST

11 Data Collection Procedure Cell phone records obtained for consecutive five-day period from providers that AirSage has partnership with Through trips not completed within 12 hours considered I-E trips Zone designations» Home - where phone is detected during hours typically considered home time 7pm to 7am» Work where phone is detected during hours typically considered work time 9am to 4pm Study conducted from 12/12/2010 to 12/18/

12 Data Collection Procedure (Cont d) Four subscriber classes» Residents Observed for at least half the weekdays during study period» Visitors Nonresidents in the study area Entered greater than 12 but less than 24 hours before they left Not given a work zone designation» Inbound Commuters Similar to visitors/through travelers but actually have a designated work zone within study area» Through travelers All other observations 12

13 Matrix Post Processing Matrix cleaned up» Diagonal values removed» Aggregated stations disaggregated using observed traffic count percentages» Megazone labels converted to External Station IDs using lookup table Matrix Imported into TransCAD Matrix Balanced 13

14 14 Matrix Post Processing (Cont d)

15 Results Raw data results are provided for each phone identified» Facilitates further post processing if desired» Unique record for each observation pair 15

16 Results Data File structure» Sub (encrypted subscriber ID of device)» Class (subscriber class as described earlier)» Epoch (Unix IT time)» Origin (origin megazone)» Destination (destination megazone)» Via (megazone via which phone traveled to get to exit station)» Duration (elapsed time in seconds from origin to destination megazone)» Origin-Time (time of last device detection in megazone) 16

17 Results (Cont d)» Destination-Time (time of first device detection in megazone)» Origin_MZ_Class (type of origin megazone)» Dest_MZ_Class (type of destination megazone) Data also reported in a pivot table matrix format by megazone ID Lookup table used to get External Station ID 17

18 Results (Cont d) Some megazones contain aggregated external stations» Stations are close; separation not possible for grid cell determination» Traffic counts used to divide up volumes among such stations Example of aggregated external stations» ST8 contains four external station megazones: Station 831 Station 832 Station 833 Station

19 General Observations Total derived E-E trips lower than TransCAD fratared 2010 E-E trips» 18,855 versus 35, Attributable to the fact that observed cell phone data is a sample of total trips» (only vehicles that had cell phones that were connected to the network)

20 General Observations (Cont d) Some lower class facilities have unexpectedly high values» May be a result of assumptions regarding through trip time frame 12 hours was used as cutoff» Grid cell size Map gives a visual depiction of the derived Airsage O-D trips 20

21 Conclusions Higher cost full external O&D survey would yield more comprehensive results; however, use of cell phone data for origin and destination data appears to be acceptable starting point Attention will need to be paid to handling the outlier numbers on smaller roads Smaller grid cells may be preferable Better indicator of trip patterns than previous external O- D roadside survey conducted on ramps, weigh stations Sample results will need to be factored up to the full universe during model validation process 21

22 Chattanooga Cell Phone External O-D Matrix Development Questions? Presented to Tennessee Model Users Group (TNMUG) November 10,