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A tour-based microsimulation approach to modeling destination choice and mode choice of San Francisco residents is presented. These models were developed as part of an overall tour-based travel demand forecasting model (SF model) for the San Francisco County Transportation Authority to provide detailed forecasts of travel demand for various planning applications. The models described represent two of the nine primary components of the SF model. Both model components consist of multiple logit choice models and include both tour-level models (which refer to the primary activity of the tour) and trip-level models (other activities on the tour). A separate model was estimated for each tour purpose, including work, school, other, and work-based. The destination choice models combine the trip attraction and trip distribution components of the traditional four-step process and use a multinomial logit specification. The mode choice models utilize a nested logit formulation to capture the similarities among sets of similar modes. The two models are linked by incorporating the mode choice utility logsum in the destination choice models; the result is equivalent to a nested structure with a mode choice nest under destination choice. It is demonstrated that the microsimulation approach easily allows the inclusion of a number of key variables in destination and mode choice models that have a significant explanatory power compared with those in traditional models. It is also shown that this approach allows estimation of the effects of tour characteristics on the choice of destination and mode using widely available data and estimation procedures.

Abstract:Temporal wet-season trends from 1987 to 1998 of total N and total P concentrations (TN and TP, respectively) in 14 tributaries to the Swan-Canning Estuary in Western Australia were evaluated using the Mann-Kendall or Seasonal kendall tests. Six of the catchments drained clay soils primarily on the Darling Plateau, which borders the sandy coastal plain on the east; two rural catchments drained the coastal plain; and six urban catchments drained the coastal plain. Generally, TN and TP were lower in tributaries draining clay soils than in tributaries draining siliceous sandy soils. Annual median TN and TP were relatively constant and no trends were detected in tributaries draining clay soils. TN and TP were higher (median TN D 1Ð6 and TP D 0Ð1 mg l 1 ) and more variable temporally in tributaries draining the coastal plain. Statistically significant (˛< 0Ð01) TN trends were detected in 50% of the urban coastal plain tributaries and most were decreasing ( 0Ð07 to C0Ð53 mg l 1 year 1 ). Decreasing TP trends were detected at the two rural coastal plain tributaries and two of the urban drains ( 0Ð01 to 0Ð15 mg l 1 year 1 over periods from 5 to 12 years). Flow adjustment of TN and TP was responsible for removing trends in the raw data at some sites. The inter-annual variability of TN and TP of coastal plain tributaries was also related to the proximity of the water table to the land surface, which in turn was related to the annual precipitation. Fixed-interval sampling may be able to detect TN and TP changes associated with the implementation of management strategies in sandy coastal plain catchments. Tributary sampling during rainstorms and continuous monitoring of discharge are needed to better define processes controlling nutrient flux and concentration variability, and to detect trends in the urban catchments and the clay soil catchments, primarily those draining the Darling Plateau.

Traditionally, mode choice models distinguish between drive-alone and shared ride modes, leaving the network assignment models to predict the assignment of vehicles to toll and high-occupancy vehicle (HOV) facilities. If the shortest generalized cost path in the user equilibrium assignment is a toll or HOV path, the trip becomes a toll or HOV trip. Mode choice models that include the use of general-purpose highways, toll roads, and HOV lanes simultaneously with the choice of the drive-alone and shared ride modes are developed. Multinomial logit and nested logit models are estimated for this full set of alternatives. The models are estimated from a sample of data enriched by special surveys of toll, HOV, and transit users in the Houston, Texas, region. These data provide an empirical basis for studying the behaviors of toll and HOV facility users that is not normally available. The results indicate that the time saved by using these facilities has a higher utility weight than the time differences between other modes. Furthermore, for each mile traveled on a toll or HOV facility, there is an additional benefit that is partially offset by any excess in total travel distance necessary to use the toll or HOV facility. The additional preference for toll and HOV facilities can be explained by a perception of lower travel time, less driving stress, and higher reliability on these facilities. These results suggest that selection of a least-cost path in trip assignment is not sufficient for modeling the use of toll and HOV facilities.

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