Dr. Mengying Cui: Full cost accessibility


Congratulations to soon-to-be Dr. Mengying Cui for successfully defending her dissertation: ‘Full cost accessibility’  at the University of Minnesota campus on 8 May 2018.


Accessibility measures the ease of reaching destinations, and is the product of a function of the cost of travel between two points and the number of opportunities at the destination. That cost is usually represented as individual travel time, and occasionally as time and out-of-pocket monetary costs. Thus, it fails to fully capture travel costs, especially the external costs, of travel. This study develops a full cost accessibility (FCA) framework combining the internal and external cost components of travel with accessibility evaluations, to provide an efficient evaluation tool for transport planning projects.FullCost_10D

The FCA framework includes three major steps: analyzing cost components of travel, proposing new path types, and performing FCA analysis. The cost analysis distinguishes the internal and external costs of travel for alternate cost components and proposes a link-based cost model applied to each road segment in a metropolitan road network. The new path types, including the Safest and Greenest/Healthiest paths, in addition to the traditional Shortest Travel Time and Cheapest (least expensive) paths, are proposed to translate link costs into trip costs by selecting the routes with the lowest cost. For the FCA analysis, we measure the number of opportunities that can be reached in a given cost threshold.

The key cost components for travelers are categorized as time costs, safety costs, emission costs, and monetary costs. The Minneapolis – St. Paul Metropolitan (Twin Cities) region was selected as the study area to implement the FCA framework based on each of those key cost components. Our major findings indicate:

    1. The average full cost of travel is $0.68/veh-km in the Twin Cities region. Time and monetary costs account for approximately 85% of the total. It is unlikely that travelers will shift their route significantly to consider safety and emissions.
    2. Except for the infrastructure cost, highways are more cost-effective than other surface roadways considering all the other cost components, and the internal and full costs.
    3. Most new path types show largely the same spatial distribution as the shortest travel time path. However, the healthiest path, concerning the emission intake cost, detours to exurban areas where the on-road concentrations are lower; the lowest infrastructure cost path detours to local surface roadways where the infrastructure expenses are lower.
    4. Job accessibility measurements based on different cost components show similar spatial distribution patterns. Accessibility decreases with the distance to the downtown area. Slight differences exist depending on the properties of cost components.
    5. Accessibility difference assessment reveals a cost-benefit trade-off showing that travelers will save $0.24/veh-km of full cost on average based on the lowest full cost path rather than the shortest travel time path by paying a time-weighted accessibility loss of 191 jobs.

This dissertation demonstrates the practicability of the FCA framework in metropolitan areas.