For the development of the economic scores, we used the TREDIS economic model to estimate each project's impact in terms of additional dollars in the economy, or Gross Regional Product (GRP). TREDIS compares two separate situations to find the additional economic benefit gained from the implementation of the project in question. The two scenarios are the “Build” scenario, where the project is constructed and the “No-Build” scenario, where the project is not constructed. The majority of the projects only have data input into the build scenario, while the no-build scenario is used as a control. More in depth model information can be found here .
The TREDIS model has five separate areas where we can input data. These “buttons” are as follows:
Safety benefit – Assume that crash rates would drop to the statewide average for highways similar to the new roadway; for example, if the project widened the road to a 4-lane expressway, the statewide average crash rates for 4-lane expressways were assumed. If this was not an improvement, the rate was left unchanged. This category does not result in new jobs, and only a modest economic benefit.
Travel benefit – Assume higher speeds and recompute travel time, and incorporate distance saved, if applicable. This is amount of benefit is added to vehicle that is affected by the project and the total traveler benefit is over twenty years (assumed to be 2030 in this case). Depending on the number of vehicles affected by this project and the savings, the total can be quite significant.
Reliability benefit – There needs to be congestion on the segment first before this is an issue. We tell TREDIS how much of the travel occurs in congested conditions in the no-build and build, and also how much buffer time changes. The definition of congestion is based on the industry-standard Highway capacity Manual. Congestion related travel time (buffer time) is the amount of time a traveler must add to their trip to avoid being late from congestion 19 out of 20 times. These reliability improvements have sizeable economic implications.
Market access benefit – We tell TREDIS how many people are within a 40 minute drive of the study area, in the no-build and build cases. I only applied this in about ¼ of all the projects, as it requires either a new linkage, or relief of a bottleneck that acts similarly to a new linkage. This has game-changing implications, especially in the metro areas where there are lots of people located on that 40 minute fringe.
Contingent development benefit – The primary reason for the Area Engineer surveys, we tried to limit to development that would only happen if the project were constructed . We also went back to the most likely candidate projects (new linkages or major widening) and asked local EcoDevo directors for their estimates of contingent development. These were translated in to jobs by sector and placed into TREDIS. Some of these made a significant impact.
Once data has been input to each of these categories, we run the model and obtain the results. There are many outputs from the model, but we just focused on the permanent jobs created and the GRP+Traveler Benefit (GRP+B).
After much discussion, we decided that the cost of a project should be a factored into the economic score. To do this, we took the GRP+B and divided it by the project cost. While this is not a "true" benefit to cost ratio, it is a similar metric. These results were the banded and assigned a score ranging from 1 (lowest) to 25 (highest). Separate banding schemes were used for Urban and Rural projects.
This is a short explanation of the methodology used for obtaining the economic development scores. Additional questions can be answered as they arise and this blog will be expanded.
But here at KDOT, we need local help. We have limited information for the Contingent Development button and are continuing to gather information. If you, or anyone you know may possess any development information for a particular project feel free post it here or send me a message. I cannot guarantee it will get placed into the model, but any lead will be investigated further.