Case Study:

Tren Urbano

Application

Regional Accessibility

Baseline Accessibility

The study authors first examined existing 1990 accessibility levels. The automobile mode provides by far the highest regional accessibility scores. The accessibility pattern illustrates the radial nature of the road system, with jobs highly concentrated at the core, as accessibility declines in a ring-belt pattern away from the core area (Figure 3).

Figure 3. Employment Accessibility by Automobile

Source: Zhang, Shen, and Sussman (1998).

Accessibility levels for transit are generally much lower, and show varying patterns depending on the system. Bus accessibility, for example, is greatest along a north-south corridor that represents the core service area (Figure 4). Publico service is generally provided outside of bus service areas. The difference in accessibility scores between the different modes represents the difference in travel impedance, since the spatial distribution of employment and population is fixed.

Figure 4. Employment Accessibility by Bus

Source: Zhang, Shen, and Sussman (1998).

Table 1 shows how the auto and transit accessibility scores vary across income groups. For the auto mode, the high income areas have greater accessibility than low-income areas. For transit, higher accessibility scores are observed at both ends of the spectrum, with the highest accessibility at the high end of the income spectrum. This indicates that both low-income and high-income populations tend to be located in areas well-served by transit.

Table 1.
1990 Base Case: Population-Weighted Average Accessibility Scores and Indices by Income Group

Tren Urbano Impacts

The next step was to compare employment accessibility under the 2010 Tren Urbano Build and No-Build cases. Figure 5 compares the auto and combined public transit accessibility indices for each case. Construction of Tren Urbano, along with related transit service improvements, increases the regional transit accessibility score from 770 to 999, an increase of 30 percent. Examining results by income level, all income groups are better off in the Tren Urbano Build Case but worse off in the No-Build Case, compared to the 1990 base. Examining the relative accessibility indices by income group, the higher-income zones appear to gain somewhat more on average than the lower-income zones. Figure 6 shows the change in accessibility by zone for the Build versus No-Build alternatives. (Note that this analysis does not account for potential redistribution of income groups in the future, or for actual ridership by income group.)

Figure 5. 2010 Population-Weighted Average Accessibility

Source: Zhang, Shen, and Sussman (1998).

Thus, the authors conclude, the rail system will have accessibility benefits for the region. However, these benefits will be highly localized along the rail alignment, and will not necessarily decrease the inequity in mobility among different population groups.

Figure 6. Change in Accessibility, Build versus No-Build

Source: Zhang, Shen, and Sussman (1998).

Other Policy Impacts

The research team also examined the impacts of two additional regional policies:

1. Systemwide transit service improvements by mode (represented by a 10 percent decrease in travel time for each mode); and
2. Land use changes, specifically, increased development in rail station area zones.

Transit service improvements. A 10 percent reduction in zonal travel times by rail was found to have the greatest effect on job accessibility, raising the aggregate score from 1,073 to 1,196. Publico improvements had similar results. Compared to rail improvements, however, Publico improvements had the effect of decreasing rather than increasing the difference in accessibility indices between the lowest and highest income groups. Improvements to the bus service had only a small effect, due to the relatively small geographic coverage of the bus system and low operating speeds. The authors note also that there are institutional barriers to improving Publico service, while the barriers to increasing rail operating speeds are technical.

Land use changes. The research team also examined the impact of clustering development in rail transit station areas. They did this by first identifying TAZs that fell completely or partially within a quarter-mile vacant developable land (as determined from the regional land use database) contained in these TAZs was summed. Two scenarios were created, in which this land was assumed to be developed at residential densities of 10 and 18 dwelling units per acre, respectively. Population was then reallocated to these TAZs and removed from other TAZs in proportion to the growth increment of each TAZ between 1990 and 2020.

All else being equal in the 2010 Tren Urbano Build Case, clustering new development in transit station zones resulted in an increase in transit accessibility levels from 1,073 to 1,124 or 1,165, for the 10 and 18 dwelling unit per acre scenarios, respectively. Accessibility increased for all five income groups. The effect of clustering employment as well as residential uses was not measured, but this would make an interesting additional comparison.

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