Figure 11 TRIMMS – Price and Travel Time Elasticity Parameters Modification
User Supplied Final Mode Shares
The model’s strength is its capacity to estimate the impact on final mode shares of a given policy or strategy. This is accomplished by means of the constant elasticity of the demand model as described earlier in the report. Whenever the user possesses specific information or a guess estimate about the potential impact a given policy might have on final mode share, he or she can override the model by manually entering the values. This option is accessible from the “Financial Incentives,” “Travel Time Improvements,” and “Soft Program Evaluation” worksheets by clicking on the “Supply Final Mode Shares” button. This opens a window as displayed in Figure 12. The user enters the new mode shares (in percentage points) and then clicks the “Ok” button. A final warning displays to confirm the decision to over ride the model. The model can always be reset by clicking on the “Model Reset” button.
If the user supplied shares sum is not equal to 100 percent, a warning message informs the user of this imbalance. Nonetheless, the model automatically rebalances the final mode share to total 100 percent. Note that although the “Model Output” worksheet displays the user supplied final mode shares, the balanced shares are used to compute impacts.