The Illinois Department of Transportation (IDOT) and the Iowa Department of Transportation (Iowa DOT), with the Federal Railroad Administration (FRA) evaluated alternatives for the reestablishment of passenger rail service between Chicago, Illinois, and Iowa City, Iowa, as part of the Midwest Regional Rail Initiative (MWRRI). Development of National Environmental Policy Act (NEPA) documentation and preliminary engineering design was divided between the state transportation departments. The selected alternative involved operating the new service line over two existing rail networks: the BNSF Railway and Iowa Interstate Railroad (IAIS). Substantial infrastructure improvements to the IAIS line were determined necessary during the preliminary design phase to establish reliable on-time service performance for passenger rail. To support the Environmental Assessment (EA), a technical memorandum was prepared to determine tree densities through the IAIS project corridor in Illinois.
Prairie Engineers of Illinois conducted a study to document the average tree densities within railroad right-of-way at three separate locations throughout the Iowa Interstate Railroad study corridor. The purpose of the study was to determine if aerial photography could be used to estimate tree densities, and whether the densities were consistent enough throughout the corridor to allow impacts of proposed project improvements to be estimated using aerial photography. The study used aerial photography to classify areas into “low”, “intermediate”, and “high” tree density areas. Multiple sample plots were taken within each classification area at three different locations spread across the corridor. Statistical analysis was conducted between the same classification groups within the same sampling site and between sampling sites; and conducted between different classification groups within the same sampling site and between sampling sites to determine goodness of fit for the classification designations. The sampling verified the designated classifications generated from interpretation of aerial photography were valid within the IAIS corridor.
The validation of the classification system and establishment of associated classification densities allowed the program to quickly estimate the number of trees removed within proposed construction footprints. The classification densities system expedited the estimation process as alterations to the construction footprint occurred during the preliminary design phase.