Bet you didn't think you could Route Trucks LIKE THIS!

Abstract

Introduction

This project involves potential roadway improvements to facilitate the circulation of truck traffic and reduce negative impacts created by current designated truck routes through and around the Town of Harrington. The proposed improvements may consist of maintaining the existing route, the upgrade of existing roads serving as the current route, the re-designation or upgrade of other roads to serve as a new route, and intersections and/or construction of a new alignment.

The primary goal of this study is to develop and evaluate transportation improvements that facilitate the movement of trucks through and/or around the town of Harrington. In addition, a goal is to minimize negative effects created by trucks on the communities and on historic structures within the designated or identified historic districts within the town.

Existing Process

In order to develop effective improvement alternatives, the specific transportation problems within the study area must be determined and documented. Therefore, a data collection effort was undertaken in the spring and summer of 2000. The data collection effort included: twenty-four hour (utilizing ATRs) traffic data, intersection turning movement data, field reconnaissance to develop a list of truck traffic generators, and manual field counts for segments within in each study area. Additionally, area accident statistics for the last three years were compiled. Analyses included: an accident analysis, and intersection and segment levels of service analyses, and a projected growth impact analysis on levels of service.

Each of these was collected through an exhaustive data development phase resulting in a massive data set, which was at the disposal of the design team.

A physical evaluation of the existing transportation facilities was then performed. The goal of this analysis was to identify physical deficiencies or limitations that may exist for trucks traveling through the town. This analysis included evaluating roadway cross-sections, intersections and other related traffic circulation issues, such as the provision of on-street parking. The evaluation of roadway cross sections included determining overall cartway, travel and parking lane widths along the entire length of identified routes within the study area. In addition of the factors, such as average building setbacks were evaluated. All intersections along the identified routes were evaluated for turning movement deficiencies. This included developing intersection diagrams and measuring turning radii for each movement. The likelihood of conflicts between truck traffic and automobile traffic at intersections was evaluated based on field inspections. In addition, other potential conflicts between truck and automobile traffic were evaluated, such as in areas where on street parking is provided.

The next step of the process was for the planning team worked with the client to generate multiple plausible, and less-plausible, truck routing alternatives, given the physical constraints of the study area. This process generated over 15 individual segments that could be utilized as potential routes. This complexity of alternatives greatly reduced the ability of the team generating these alternatives to weigh evaluation criteria in an impartial way.

A set of public meetings was then held in the town to educate the residents on the issues involved in the trucking study, demonstrate the 15+ potential solutions, and gather input from the residents on the potential impacts each alternatives might have. However, the information and vast knowledge gained from these meetings was never utilized to its fullest potential. It appeared that the deep residential knowledge base could never really be used with the existing planning model because there was no mechanism in place to feed this information into the evaluation and selection process of the chosen alternative. It was during this phase, the public meeting phase, that the GeoDecisions GIS team member supporting the project began to develop an alternative method of evaluating and choosing a potential truck route utilizing advanced raster analysis software at his disposal.

ArcView Spatial Analyst and Model Builder

Proposed Strategy

Determining the criteria to evaluate all potential alternatives remained the first step in the process. This would collect as much data as possible on the following data layers to be developed:
Existing road infrastructure
Road segment travel length
Rail crossings
Potential route turning locations
Truck generators
Fire stations
Schools
Parking lots
Historic district boundaries
Historic/Archeological sites
Parcel boundaries
Zoning
Land use
Wetlands
Hydrology
Soils

These data were collected and converted to a raster format through various methods. Point data elements such as schools and fire stations were spread from using the Find Distance routine. Other linear data elements such as rail crossings, parcel boundaries and road infrastructure were similarly spread from to generate raster surfaces evaluating the proximity of every grid cell from the origin feature. Polygon data layers were converted to raster surfaces based on values of the feature (eg. Zoning codes). Each data layer was then normalized on a scale from 1 to 10 based on assumptions made by the consulting planning team. Examples of these assumptions for the purposes of this routing analysis were:
Trucks should not be routed in close proximity to schools. A grid cell adjacent to the school received a value 10, while a grid cell far away from the school received a low value.
Trucks should utilize existing rail crossing as much as possible. A grid cell on an existing rail crossing received a low score (1), while a grid cell not directly on an existing rail crossing received a high score.

The next step in the process was to develop an interface for ArcView GIS using dialog designer that could assist a public participant in the process in weighting the individual criteria. The dialog would have slider bars based on a percentage (0-100%) to record their relative importance in the mind of the scorer and would sum to 100%.

The resulting scores would be entered into the final Model Builder step to weight the combination of each criteria to generate the resulting cost, or friction, surface. This surface would have values from 1 to 100 based on the total score that each grid cell received. A high value meant that the grid cell would have a great cost if an alternative route passed over it, while a low score meant that that grid cell was conducive for use in an alternative route segment.

A public participant would then choose an alternative to judge, given the cost surface that they developed. The alternative would then be overlayed on the cost surface and the tabulation of each grid cell covered would be automated. The resulting score could then be recorded by the participant of the process.

At this stage the participant was free to change the cost surface by re-weighting a particular criteria. They could also evaluate a different alternative route for trucks on the original cost surface. This iterative process could greatly increase the general understanding of the planning process.

The final step was to compare the participants score for a particular alternative with that of a neighbor, or a business owner, or with someone from the design team, or with a representative from a trucking company. This would hopefully generate discussion on the issues that are important to many of the constituents of the project.

Conclusions

This process was, unfortunately, never implemented in real situations within the Harrington project. Time constraints prohibited its use in any of the public meetings. But, the idea and innovative strategy provided inspiration for future changes in the way the planning team conducts similar projects.