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- 1. Mode Choice • Inmost situations, a traveler has a choice of modes – Transit, walk, bike, carpool, motorcycle, drive alone • Mode choice/mode split determines # of trips between zones made by auto or other mode, usually transit
- 2. Characteristics Influencing ModeChoice • Availability of parking • Income • Availability of transit • Auto ownership • Type of trip – Work trip more likely transit – Special trip – trip to airport or baseball stadium served by transit – Shopping, recreational trips by auto • Stage in life – Old and young are more likely to be transit dependent
- 3. Characteristics Influencing ModeChoice • Cost – Parking costs, gas prices, maintenance? – Transit fare • Safety • Time – Transit usually more time consuming (not in NYC or DC …) • Image – In some areas perception is that only poor ride transit – In others (NY) everyone rides transit
- 4. Mode Choice Modeling •A numerical method to describe how people choose among competing alternatives (don’t confuse model and modal) • Highly dependent on characteristics of region • Model may be separated by trip purposes
- 5. Utility and DisutilityFunctions • Utility function: measures satisfaction derived from choices • Disutility function: represents generalized costs of each choice • Usually expressed as the linear weighted sum of the independent variables of their transformation U = a0 + a1X1 + a2X2 + ….. + arXr U: utility derived from choice Xr: attributes ar: model parameters
- 6. Logit Models • Calculatesthe probability of selecting a particular mode p(K) = ____eUk__ eUk p: probability of selecting mode k
- 7. Logit Model Example1 Utility functions for auto and transit U = ak– 0.35t1 – 0.08t2 – 0.005c ak = mode specific variable t1 = total travel time (minutes) t2 = waiting time (minutes) c = cost (cents)
- 8. Logit Model Example1 (cont) Travel characteristics between two zones Uauto = -0.46 – 0.35(20) – 0.08(8) – 0.005(320) = -9.70 Utransit = -0.07 – 0.35(30) – 0.08(6) – 0.005(100) = -11.55 Variable Auto Transit ak -0.46 -0.07 t 1 20 30 t 2 8 6 c 320 100
- 9. Logit Model Example1 (cont) Uauto = -9.70 Utransit = -11.55 Logit Model: p(auto) = ___eUa __ = _____e-9.70 ____ = 0.86 eUa + eUt e-9.70 + e-11.55 p(transit) = ___eUt __ = _____e-11.55 ____ = 0.14 eUa + eUt e-9.70 + e-11.55
- 10. Logit Model Example2 The city decides to spend money to create and improve bike trails so that biking becomes a viable option, what percent of the trips will be by bike? Assume: • A bike trip is similar to a transit trip • A bike trip takes 5 minutes more than a transit trip but with no waiting time • After the initial purchase of the bike, the trip is “free”
- 11. Travel characteristics betweentwo zones Uauto = -0.46 – 0.35(20) – 0.08(8) – 0.005(320) = -9.70 Utransit = -0.07 – 0.35(30) – 0.08(6) – 0.005(100) = -11.55 Ubike = -0.07 – 0.35(35) – 0.08(0) – 0.005(0) = -12.32 Variable Auto Transit Bike ak -0.46 -0.07 -0.07 t 1 20 30 35 t 2 8 6 0 c 320 100 0 Logit Model Example 2 (cont)
- 12. Uauto = -9.70,Utransit = -11.55, Ubike = -12.32 Logit Model: p(auto) = _____eUa ____ = _______e-9.70 ______ = 0.81 eUa + eUt +eUb e-9.70 + e-11.55 + e-12.32 p(transit) = _____eUt__ __ = ______e-11.55 ______ = 0.13 eUa + eUt +eUb e-9.70 + e-11.55 + e-12.32 p(bike) = _____eUt__ __ = ________e-12.32 ______ = 0.06 eUa + eUt +eUb e-9.70 + e-11.55 + e-12.32 Notice that auto lost share even though its “utility” stayed the same Logit Model Example 2 (cont)