Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 182


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 181
and from the surveys. There is, therefore, an implicit assumption that the cost functions in the model reflect the thought processes of the traveler. TRANSIMS is one of the new generation of behavioral travel models and as such is still under development. As its validation process continues, much optimism has been expressed about its capabilities. However, one of the limitations we observed is that it is not sensitive to certain geometric factors, such as lane width, and the length of both acceleration and deceleration lanes. In addition, the microsimulator has been found to be inaccurate in predicting the velocities of individual vehicles along weaving sections of highways.4 Results and their presentation. As long as a region is defined by a set of vertices, user-selected data can be drawn, and this capability facilitates the display of data aggregated into regional areas. Users can manipulate three-dimensional objects using the Output Visualizer's graphical user interface. Getting the Output Visualizer to generate output is facilitated by an extensive, user-friendly system of menu options. Moreover, by setting a configuration file key, this module can be run remotely to produce images that may be incorporated into reports, presentations, or motion pictures. Assessment. According to the FHWA, TRANSIMS will enable planners and citizens to have a better understanding of the effects and implications of transportation policy choices. It provides planners with the means to evaluate proposals to enhance the serviceability of the highway system, as well as transit, bikeways, and pedestrian amenities. The FHWA further surmised that the fine level of detail afforded by the software would not only more accurately represent the impact of transportation movements on travel, driving, and air pollution emissions but would also aid in the assessment of the socio-economic impacts of proposals for improvements (Public Roads 2000). The latter capability underlines the importance of this model as a valuable tool in assessing environmental justice concerns in the foreseeable future. Models such as TRANSIMS, however, have large data requirements and therefore would require a major commitment of resources by an agency. STATE OF THE PRACTICETRANSPORTATION CHOICE Equity is perhaps the most important goal served by increasing transportation choice. Some members of a community may not be well served by the automobile-oriented transportation systems prevalent in most U.S. cities. Lower-income populations, children, and people with disabilities are often particularly sensitive to restricted transportation choice because they tend to walk and cycle more than average and are more vulnerable to barriers and risks. Transportation disadvantage refers to people who face significant, unmet transportation needs. The four attributes below are key determinants of whether an individual or group is transportation disadvantaged: 4 Weaving is the crossing of two streams of vehicular traffic traveling in the same direction along a significant length of highway without the aid of traffic control devices. Capacity is significantly reduced in these weaving areas because drivers from two upstream lanes compete for space to merge into a single lane and then to diverge into two different streams. 186

OCR for page 181
Nondrivers People who cannot drive or do not have access to a motor vehicle. Low-income persons Drivers and nondrivers whose basic transportation needs are significantly constrained by financial limitations, especially out-of-pocket costs. Disabled persons People who have physical disabilities that limit their ability to travel independently. Automobile-dependent people People who live in a community with automobile- dependent transportation and land use patterns. A person with any one or two of these attributes is not necessarily transportation disadvantaged. For example, individuals who use a wheelchair are not transportation disadvantaged if they can afford an automobile and chauffeur or can drive and live in a community with good universal access (i.e., one designed to accommodate people with a range of needs, including wheelchair users, people with visual disabilities, and pedestrians pushing strollers or handcarts). On the other hand, the greater the number of these attributes a person has, the more likely he or she is to be transportation disadvantaged. Obtaining information on the number of people with attributes associated with being transportation disadvantaged may be difficult. Table 7-2 describes some indicators that may be used when more specific data are unavailable. There is considerable overlap among these categories. One should try to identify the number of residents who have multiple attributes, such as lower-income, employed, single parent, and low-income with disabilities. Table 7-2. Indicators of transportation disadvantage and possible data sources Indicator Data sources Households that do not own an automobile Census, NPTS, consumer surveys, and local (sometimes called zero-vehicle households) transportation surveys People with significant physical disabilities Social service agencies and special surveys Low-income households Census, household, and labor surveys Low-income single parents Census, social service agencies, and special surveys People who are too young or old to drive Census and other demographic surveys Adults who are unemployed or looking for work Census and labor statistics Recent immigrants who cannot drive Census, social service agencies, and special surveys Note: NPTS is the National Personal Transportation Survey, available at http://www.bts.gov. Although not everybody in these groups is transportation disadvantaged--and not everybody outside of them has their mobility needs satisfied--these populations may be used as surrogates if better data are unavailable. Table 7-3 suggests which modes tend to be particularly useful for various user groups. 187

OCR for page 181
Because their transport options are constrained, people who are transportation disadvantaged can be seriously affected by even relatively small changes in transportation systems. For example, low-income nondrivers may be highly dependent on a particular walking path or transit route. Changing that route may have major repercussions on their access to destinations important to them. To the greatest possible extent, it is important to use data collection and analysis methods that can identify such effects. Occasionally, this may require different analysis techniques than are used in conventional transportation planning. Table 7-3. Modes that are particularly important for specific user groups Low- Non- income Disabled Mode drivers persons persons Commuters Walking A A B B Bicycle A A -- B Taxi A B B -- Fixed-route transit A A B A Paratransit B A A B Automobile -- B B A Ridesharing B A B A Note: A = primary mode; B = potential mode. A preliminary, qualitative analysis of a project's effects on transportation choice should be conducted for all projects. Relatively detailed analyses are useful whenever a project: Widens an existing road; Is expected to increase traffic volumes; Eliminates or moves a transit stop, trail, sidewalk, or other nonmotorized facility; Reduces the shoulder width of the road or adds shoulder rumble strips; Increases the length of city blocks; Increases the number of driveways that intersect nonmotorized facilities; and Increases the incline of pedestrian or bicycle facilities. In most cases, an understanding of the transportation choices available within a community provides vital information for cities and regions trying to enrich the opportunities for non- motorized transportation as part of their demand management goals. The following four general steps are suggested for analyses of the extent to which protected populations have a choice of transportation modes and services: 188