In many cases, only the final design stages of corridor project requires the accuracies provided by conventional photogrammetric processing. Use of remote sensing opens up the possibility of limiting expensive and time-consuming photogrammetric work to the final alignment of the corridor. New more sophisticated methods of surface mapping, light Detection and Ranging (LIDAR), and digital photography may be used for planning stages resulting in a more targeted photogrammetric data collection process. This latter process could be limited to a much smaller area, thus reducing time and cost.

LIDAR data has great potential in expediting the planning and location stages but is not currently capable of replacing photogrammetric data in the final alignment design. Designers will be able to start preliminary analysis much sooner through the use of LIDAR data. Environmental conditions (e.g. sun angle, leaf off, cloud cover) will not delay the process with LIDAR to the degree they do with photogrammetry. Aerial imagery and LIDAR data can be collected concurrently, thus decreasing the days during the year when data cannot be collected. The increased availability of data would allow terrain to be analyzed earlier in the location process, allowing potential problems and issues to be identified and addressed earlier. LIDAR data has an advantage early in the siting process and photogrammetry is favored when more intensive data analysis is needed to define final corridor alignment. Using LIDAR data can produce time and cost savings through more expedient data collection on a large corridor scale; more costly time consuming methods would only needed on a much more limited area.

Washington I-405 Corridor
Background
Collaboration among the Washington State Department of Transportation (WSDOT), Oak Ridge National Laboratory, ERDAS, Inc., Space Imaging, the U.S. Environmental Protection Agency, Wisconsin DOT, and the Puget Sound Regional Council initiated an effort to document the use of remote sensing to find faster and better ways of completing the environmental assessment processes required for transportation corridors like Washington State's I-405 Corridor. The overall project consisted of over 150 smaller projects. The region has some of the most stringent state and local environmental regulations in the nation. The environmental assessment processes, under the National Environmental Policy Act (NEPA), were initiated in 1998 and completed in 2002. This project's major objective was to demonstrate and assess the applicability of commercial remote sensing products and spatial information technologies to environmental analysis in transportation planning, using the I-405 corridor in Washington State as a test case.

Methods Used
The Washington case study involved a very large number of projects and used a survey method in conjunction with project costs to determine cost and time savings associated with remote sensing. This case study divided the environmental planning studies into different "disciplines" and focuses much of its economic analysis to determine the varying levels of benefits that remote sensing delivered to the different disciplines. The Washington case study not only addressed possible reductions in time and cost associated with remote sensing technology but also attempted to evaluate the potential increase in value of the remote sensing data generated analysis.

A major complication in using this "disciplines" approach to estimate costs of the remote sensing/GIS products is that remote sensing data is not collected separately for each discipline. Typically much of the Land use and land cover (LULC) classification is done simultaneously for different disciplines. Because costs were not collected separately for each discipline, an average cost per discipline was estimated by dividing by the number of disciplines in which LULC maps were used. The costs of developing, compiling, and presenting the information, data, and maps in the environmental impact statement were obtained from the contractor team responsible for the different disciplines. Time estimates to complete the remote sensing/GIS and Environmental Impact Statement (EIS) products were based on the actual calendar time, not person months or full time equivalent time calculations.

The study noted several cost advantages to using remote sensing techniques that were not able to be assessed or documented in this study: economies of scale, geographic scale, and transferability, Economies of scale are realized through the ability to complete LULC classification for several LULC categories concurrently. Geographic scale benefits result from decreasing incremental cost of increasing study area. Cost advantages are also associated with transferability of classification algorithms to many sites.

Potential increased value of the remote sensing/GIS products was estimated through a survey to potential users asking that they assess the value and usefulness of the products. It is important to note that the increased value discussed in this case study result from a survey of 13 respondents and not from remote sensing experts. Information about the value of the remote sensing/GIS products, their usefulness, and suggestions for improvement were requested. Some respondents provided answers for disciplines separately, some answered for all disciplines in general.

Results
Cost Comparisons – Table 1 lists the costs of completing the environmental impact statement for each of the 11 disciplines. The first and third columns report cost and time respectively, using the traditional method and the second and fourth columns provide estimates of cost and time using remote sensing/GIS methods. The average cost of producing the remote sensing/GIS products was about $6,000 per environmental discipline. With remotely sensed imagery, data processing time and costs and the time and costs of producing maps and related spatial statistics increase marginally with the number of environmental disciplines. That is, the total time and cost of developing remote sensing/GIS products for eleven disciplines is not much greater than the time and cost for one discipline. The estimated time to complete the products was eight months for all products and disciplines.

Table 1: Cost and Time Comparison - Cost and Time of Producing the Draft Environmental Impact Statement (DEIS) Section on the Environmental Discipline and the Corresponding Technical Expertise Report, Compared to the RS/GIS Products

Value – Table 2 provides the survey respondents' assessments of the value of the remote sensing/GIS products developed for this study. Value is measured both in dollar terms and as a percentage of the total cost of completing work on that discipline for the EIS. Stakeholder responses are summarized in Column 2, contractors' responses are in Column 3, and other state DOTs are in Column 4.

Table 2: Range of Estimated Value of RS/GIS Products, Relative to the Cost of Completing Work on the Corresponding Environmental Discipline for the DEIS¹

Respondents' assessments of the value of remote sensing/GIS products are summarized in Table 3. Fish and aquatic habitat, land use, upland vegetation, habitat and wildlife, and wetlands assessed remote sensing/GIS products to be most valuable. Respondents from these disciplines suggested that a relatively high percentage of the work done for the EIS could be achieved using remote sensing/GIS and the value of the remote sensing/GIS products equals or exceeds its cost. Respondents from the farmland and floodplains disciplines responded judged the RS technology to be somewhat less valuable. It represented a smaller part of the overall EIS work and its value was less than its cost. The remote sensing/GIS products were least valuable for the environmental justice, recreational resources and transportation disciplines.

Table 3: I-405 Stakeholder Respondents' Relative Valuing of RS/GIS Products for Different Environmental Disciplines