Estimating Intrazonal Impedances in

Macroscopic Travel Demand Models

Matthew Bediako OkrahTechnical University of Munich

15th Transportation Planning Applications Conference

20 May 2015

Contents• Background

• Proposed Method

• Application and Suitability Checks

• Significant Observations

2

Background

• Existing approximate methods - Nearest Neighbour Techniques- Functions of Area Size

• Questions- Good estimates of intrazonal impedances?- Good estimates of intrazonal flows?

3

Intrazonal Trips

4

Intrazonal Trips

5

Proposed Method

6

Select Nodes

Calculate Weight Matrix Weighted Distance Matrix

Assign Node Weights

Compute Intrazonal Distance

Calculate Distance Matrix

Proposed Method

• Variants of Method- Unweighted Nodes- Nodes Weighted by Closeness Centrality- Nodes Weighted by Degree Centrality

7

Application of Method

• Dachau with

102 TAZ

• Area= 13 sq.mi.

• Pop= 46,000

8

Suitability Check 1

• Aggregate 102 Zones into:- 25 Zones- 10 Zones- 5 Zones- 2 Zones

• Intrazonal distance with different methods

• Compare estimated intrazonal distances

9

10

25-Zone10-Zone5-Zone2-Zone

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

RM

SE (km

)

UnweightedDegreeClosenessArea-BasedNearest Neighbor

RMSE in Estimated Intrazonal Distances

Suitability Check 2

• Trip Distribution with the different methods - Home-Work Trips - Non-Home-Based Trips- Home-Shopping Trips

• Between modeled and observed trips;- Compare TLFDs (Coincidence Ratio)- Compare Total Number of Intrazonal Trips

11

12

10987654321

25

20

15

10

5

0

Distance (km)

Perc

ent

Observed (ATL = 1.6 km)Estimated (ATL = 1.5 km)

Coincidence Ratio = 0.83

TLFD of NHB Trips (Unweighted)

Estimated Intrazonal Trips = 1215

13

10987654321

25

20

15

10

5

0

Distance (km)

Perc

ent

Observed (ATL = 1.6 km)Estimated (ATL = 1.5 km)

Coincidence Ratio = 0.83

TLFD of NHB Trips (Degree)

Estimated Intrazonal Trips = 1195

14

10987654321

20

15

10

5

0

Distance (km)

Perc

ent

Observed (ATL = 1.6 km)Estimated (ATL = 1.5 km)

Coincidence Ratio = 0.82

TLFD of NHB Trips (Closeness)

Estimated Intrazonal Trips = 1384

15

10987654321

20

15

10

5

0

Distance (km)

Perc

ent

Observed (ATL = 2.6 km)Estimated (ATL = 3.4 km)

Coincidence Ratio = 0.55

TLFD of NHB Trips (Area-Based)

Estimated Intrazonal Trips = 2136

16

10987654321

25

20

15

10

5

0

Distance (km)

Perc

ent

Observed (ATL = 1.6 km)Estimated (ATL = 1.5 km)

Coincidence Ratio = 0.82

TLFD of NHB Trips (Nearest Neighbor)

Estimated Intrazonal Trips = 1548

17

Home-Shopping(700)Non-Home-Based(1280)Home-Work(280)

60

40

20

0

-20

-40

-60

Perc

ent

UnweightedDegreeClosenessArea-BasedNearest Neighbor

Errors in Estimated Number of Intrazonal Trips

Conclusions

• Unweighted provides better estimates of

intrazonal impedances

• Better intrazonal impedance no guarantee for

better estimates of intrazonal flows

• Nearest neighbour method sufficient given

ease of measurement

• Need for smaller zones to avoid intrazonal

trips18

Thanks for your Attention

19