Guang Tian

Varying influences of the built environment on household travel in 15 diverse regions of the United States

This study pools household travel and built environment data from 15 diverse US regions to produce travel models with more external validity than any to date. It uses a large number of consistently defined built environmental variables to predict five household travel outcomes – car trips, walk trips, bike trips, transit trips and vehicle miles travelled (VMT). It employs multilevel modelling to account for the dependence of households in the same region on shared regional characteristics and estimates ‘hurdle’ models to account for the excess number of zero values in the distributions of dependent variables such as household transit trips. It tests built environment variables for three different buffer widths around household locations to see which scale best explains travel behaviour. The resulting models are appropriate for post-processing outputs of conventional travel demand models, and for sketch planning applications in traffic impact analysis, climate action planning and health impact assessment.

Traffic Generated by Mixed-Use Developments: Thirteen-Region Study Using Consistent Measures of Built Environment

Current methods of traffic impact analysis, which rely on rates and adjustments from ITE, are believed to understate the traffic benefits of mixed-use developments (MXDs) and therefore to lead to higher exactions and development fees than necessary and to discourage otherwise desirable developments. The purpose of this study was to improve methodology for predicting the traffic impacts of MXDs. Standard protocols were used to identify and generate data sets for MXDs in 13 large and diverse metropolitan regions. Data from household travel surveys and geographic information system databases were pooled for these MXDs, and travel and built-environment variables were consistently defined across regions. Hierarchical modeling was used to estimate models for internal capture of trips within MXDs and for walking, biking, and transit use on external trips. MXDs with diverse activities on site were shown to capture a large share of trips internally, so that the traffic impacts of the MXDs were reduced relative to conventional suburban developments. Smaller MXDs in walkable areas with good transit access generated significant shares of walk, bike, and transit trips and thus also mitigated traffic impacts.

A framework for correcting geographical boundary inconsistency

Spatial data quality (data accuracy, precision, consistency and so on) is a key issue in Geographic Information System. Geographical boundary inconsistency will directly affect the correctness and efficiency of analysis in GIS application. This paper describes a framework for checking and correcting geographical boundary inconsistency. Two kinds of inconsistency are identified: geometric inconsistency and topological inconsistency. Geometric inconsistency refers to the unequal of point number or coordinates of overlapping boundary. Topological inconsistency means that adjacent boundary is not able to strictly guarantee topological consistent according 9-intersection model, and generate series of gap and fragment area. Different checking and correcting methods are adopted for these two different kinds of inconsistency. In the first case, the generalized algorithm of node snapping is used, and inconsistency is solved by the mathematical methods of repeating points removing, method of averaging, method of projection, etc. In the second case, the inconsistency is solved by buffer operation, Delaunay triangulation, overlay analysis, etc. A complete framework and algorithm procedure are given in this paper to detect and correct the boundary inconsistency problem in GIS. Meanwhile, an application of inconsistency correction to land-use data based on this framework is conducted.

Testing Newman and Kenworthy’s Theory of Density and Automobile Dependence:

This study tests four hypotheses related to the much-cited work on density and automobile dependence by Newman and Kenworthy, using multivariate analysis and data for 157 large US urbanized areas. We find that density alone explains only a small fraction of the variation in vehicle miles traveled (VMT), and many confounders account for the differences in automobile dependence. We also find that it is not the localized density of individual neighborhoods that causes VMT to be lower in compact urbanized areas but rather the relative accessibility of neighborhoods to the rest of the region.

An Algorithm for Splitting Arbitrary Polygon

An algorithm for splitting arbitrary polygons with a polyline is described in this paper. Starting from introducing the existing theories in computational geometry and computer graphics, the paper describes the three major steps of this algorithm: 1) search lines with the sweep-line algorithm based on sorted edges of polygon, splitting plotline, and the most bounding rectangular determination; 2)calculate and select the intersection points, and save them in a node list together with the additional information needed in the last step of the algorithm; 3)construct the output polygons by performing independent walk-abouts through input polygons and the node list. This algorithm is able to do the common operations of arbitrary polygon splitting (convex and concave, curve edge, including finite number of holes). Also, it can split polygons with sharing edges. In the mean time,direct memory reading and overall computing strategy are adopted in implementation of the algorithm to enhance the efficiency.

An intersection points determining algorithm for polygon overlay operation

This paper describes an algorithm for determining intersection points of polygons. Additional information of intersection points is stored in an oriented single list which is used for the constructing of output polygons in overlay operation. Overlay operation is one of the most important functions in GIS spatial analysis. In GIS application, polygons are usually complex (convex or concave, with or without holes) with huge number of vertices, and also, there are two or more map layers for overlay. Therefore, this algorithm adopts overall computing strategy, picks up all edges of input polygons and sort them in one direction(overlapping edges are selected), and then determines intersecting and touching edges by sweep-line and rectangle test. In order to avoid repeating intersection points calculation, touching edges are polylinized and considered as line segments for further computing. Overall computing strategy and non-repeating intersection points are efficiently adopted in GIS overlay operation.