Toolkit for Integrating Non-Dedicated Vehicles in Paratransit Service (2007) / Chapter Skim
Currently Skimming:
Pages 22-51
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 22... ...
I. Introduction The Non-Dedicated Vehicle Optimization Model (NDV Model)
|
From page 23... ...
fleet due to the absence -- or limited number -- of wheelchair-accessible vehicles in the NDV fleet. The NDV Model allocates passenger trips to NDVs -- subject to constraints on fleet and vehicle type availability -- whenever doing so yields a more cost-efficient solution than having these trips transported on DVs.
|
From page 24... ...
demand periods of service. In the limiting case, all passenger trips during the evening period are handled by NDVs -- if input data and user-specified parameters indicate there are sufficient accessible vehicles to make this a feasible option.
|
From page 25... ...
meet these requirements, and calculates the resulting total operating cost of DVs and NDVs. This iterative process (typically requiring 10 to 30 iterations of the model)
|
From page 26... ...
the model begins by trying to assign all trips above this level to NDVs. This level was chosen to represent minimum conceivable use of DVs.
|
From page 27... ...
As shown in Figure 2, the optimal service mix requires the baseline number of dedicated vehicles (shown as black bars) plus additional vehicles (shown as diagonal hatch bars)
|
From page 28... ...
III. Working with the NDV Model This User Guide focuses on the following aspects of using the NDV Model.
|
From page 29... ...
you load the model, so you may wish to reconsider your choice of Macro security level if this is excessively annoying.
|
From page 30... ...
• Alternatively, the user can provide summary driver/vehicle run data for a typical day in which the number of vehicles in service at each time point during the day is entered in the spreadsheet and the total number of driver hours for the day is specified DRT System (Dedicated Vehicle) Driver Compensation Arrangements • Driver wage rates and benefit rates, by type of shift -- full-time, part-time, straight shift, split shift Operating Costs 1.
|
From page 31... ...
C. Derivable Data Elements The model uses other data elements that can be derived from required data, assuming data are available, and for which the spreadsheet contains calculated fields designed to generate such data.
|
From page 32... ...
32 Toolkit for Integrating Non-Dedicated Vehicles in Paratransit Service Figure 7. DRT system factors data entry worksheet.
|
From page 33... ...
data or a model-defined value (explained in the following section)
|
From page 34... ...
• Street circuity factor -- This factor, which has a default value of 1.3, is used to convert airline distance to street distance if the former is used as the basis for trip length distribution data. If the street network is a perfect grid, the street circuity factor is approximately 1.4.
|
From page 35... ...
require judgment. If the user does not enter a value in the required cell, the default value adjacent to that cell is used in the model instead.
|
From page 36... ...
36 Toolkit for Integrating Non-Dedicated Vehicles in Paratransit Service Figure 9. Non-dedicated vehicle data entry worksheet.
|
From page 37... ...
The user may wish to enter data values for the Evening column separately, even though the values will appear to be redundant since they include some of the same time periods as the Avg. Weekday column.
|
From page 38... ...
select the Calculated method of data entry, they enter the driver/vehicle runs for the dedicated vehicle operation for a typical day of the week into this worksheet, using the following format: 1. Run number (can be any number -- for user reference purposes only)
|
From page 39... ...
enables the user to control certain parameters that affect how the model will work for a particular optimization run. These parameters can be altered frequently or left largely unchanged after they have been set initially, depending on the user's needs and preferences.
|
From page 40... ...
wheelchair trips to be placed on accessible vehicles in the NDV fleet, based on the capacity of such vehicles as specified on the NDV Data worksheet. • Ambulatory trip restriction to non-dedicated vehicles -- This field should be set to "Y" only if the DRT service is based entirely on non-dedicated vehicles with a supplemental service provider to handle wheelchair trip needs.
|
From page 41... ...
B. Setting Optimization Model Parameters Before running the optimizations, the user should set or modify certain factors that control aspects of the optimization for each of the models.
|
From page 42... ...
the user to specify an upper limit on the number of such long shifts per day. The value for the 10-hour shifts per day will include 10-hour split shifts as well as 10-hour straight shifts.
|
From page 43... ...
whether they should be restricted to only wheelchair trips or can be used for general purposes as well. In general, it is more cost-effective to allow the DVs to be used for all trip purposes given that a baseline level of service will be needed to accommodate the number of evening wheelchair trips.
|
From page 44... ...
be allocated to NDVs. It is usually appropriate to set a small value for this field, typically no more than 10% to 20%, or else the optimizer may divert many short trips in attempting to satisfy the prior two constraints.
|
From page 45... ...
Do NOT choose the "Continue" option -- which is the Excel default choice -- unless you are prepared to either wait a long time for the optimizer to find a solution or to potentially abort Excel via Windows Task Manager -- since the optimization may continue to run indefinitely if you select the Continue option. Do NOT simply hit the Enter key if this pop-up appears, because the default selection is "Continue" -- which is not what you want.
|
From page 46... ...
Figure 18. Optimal split solution.
|
From page 47... ...
The middle bottom graph on this spreadsheet page shows the different run structures -- in terms of required DVs at time points during the day -- necessary for the base solution, the optimal solution, and the situation where only DVs are used. The graph to the right of this compares the current run structure and the optimal run structure generated by the model.
|
From page 48... ...
both in absolute terms and relative to both the all-DV option and the current service mix. In the example shown in Figure 20, one can conclude that, among the three models, the Evening Diversion optimization strategy (which includes the Core Model)
|
From page 49... ...
• Specify the trip length distribution for the trips to be allocated to NDVs; and • Alter policies relative to mandatory use of accessible vehicles for wheelchair trips. Any of these actions, as well as others, is likely to affect the optimum solution.
|
From page 50... ...
50 Toolkit for Integrating Non-Dedicated Vehicles in Paratransit Service Figure 22. Sensitivity analysis input parameters -- calculation factors.
|
From page 51... ...
allocation of trips to DVs and NDVs. The user can specify the maximum number of DVs and the maximum and/or minimum number of NDV passenger trips -- disaggregated by ambulatory trips and wheelchair trips.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.