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Reducing Costs While Minimizing Environmental Impacts

“The ability to quickly test a wide range of alignment options in the context of all of the key environmental and physical constraints, as well as the main design and cost parameters, was critical to achieving the objectives of this study.”
- Parsons

The California High-Speed Rail Authority (CHSRA) and Parsons Brinkerhoff used the Trimble® Quantm® system to identify potential savings for California's proposed high-speed rail system. As part of the environmental process for a proposed statewide high-speed train system, CHSRA conducted a screening evaluation of alignment options. The Northern Mountain Crossing (Diablo Mountain Range) and the Southern Mountain Crossing (Tehachapi Mountain Range) are two areas of the statewide system with alignment options and associated costs that are constrained by physical features and associated environmental constraints.

While these areas have been previously studied and evaluated, screening decisions have been difficult, due to the vast potential for variation in specific alignment (horizontal and vertical) and associated costs and impacts. Due to the potential for a wide range of impacts within the mountain passes, CHSRA embarked upon an alignment optimization and refinement effort to further clarify the screening decisions using the Trimble Quantm system. Building on the previous work, this study analyzed millions of horizontal and vertical alignments over a three-week period.

The study was intended to meet the following three objectives: 1) To confirm the general corridors considered in the screening studies to date and/or identify any other corridors of equal or greater viability that may have been overlooked in previous studies. 2) To refine the alignment options in each general corridor to identify the most viable options in terms of infrastructure requirements and impact minimization. 3) To test the sensitivity of the alignment options in each corridor to key defining criteria such as vertical grade, alignment geometry, infrastructure (tunnel, structure) costs and key environmental constraints.

The results of the Quantm alignment refinement and optimization study are compared to the alignment options developed during the alignment screening evaluation (focused on minimizing potential environmental impacts) as well as alignment options that were developed in the previous Corridor Evaluation Study, 1999 (focused on minimizing tunnel requirements and cost). Based upon the results of the Tunneling Conference, regarding safety measures, crossing fault lines and limitations to tunnel length, the Quantm study was used to minimize tunneling and capital costs. The major results from using the Trimble Quantm system are:

Southern Mountain Crossing (Tehachapi Mountains)

  • Reduce the tunnel length in the I-5/Grapevine alignment to 18 miles (29 kilometers) as compared to 28 - 35 miles (45 - 56 kilometers.)
  • The alignment options were refined to identify more viable options in the area of the major fault crossings in terms of tunnel requirements, construction difficulty and cost.
  • An alignment was identified to the east of I-5 that allows for an at-grade crossing of the San Andreas Fault zone and an at-grade or trenched crossing of the Garlock Fault zone with no single tunnel longer than 6 miles (9 kilometers) Refer to Figure 2.
  • Cut construction cost by as much as $2 billion.


  • Southern Section (Sylmar to Palmdale) - in the Soledad Canyon alignment, tunneling can be reduced from 16 miles (25 kilometers) to 5 miles (8 kilometers.)
  • Northern Section (Lancaster to Central Valley) - tunneling was reduced from 22 miles (35 kilometers) to 5.1 miles (8.2 kilometers.)
  • In the SR 138/Palmdale alignment tunnel length was minimized from 14.3 miles (23.0 kilometers) to 12.8 miles (20.5 kilometers) at 2.5% maximum grade and to 10.4 miles (16.7 kilometers) at 3.5% maximum grade.

Northern Mountain Crossing (Diablo Mountains)

  • Reducing total tunneling to 11.3 miles (18.1 kilometers) and limiting single tunnel length to just over 5 miles (8 kilometers.) The previous best route required 31 miles (49 kilometers) of tunnel.
  • Reducing the associated construction cost by up to $2.8 billion in the Diablo Range Direct alignment. Refer to Figure 1.
  • Refinement of the SR 152/Pacheco Pass alignment identified a new alignment and profile option that can potentially reduce the total required tunneling from 12 miles (19 kilometers) to 5 miles (8 kilometers.)

This three-week study identified alignment options and refinements that significantly improved on the original alignments that had been developed in previous studies, completing a task that would normally take up to 8 months. The Trimble Quantm system was particularly applicable to the screening evaluation process. It became apparent that the earlier this type of comprehensive evaluation is conducted in a corridor/alignment study, the more effective the outcome.

The study team also confirmed that the Trimble Quantm system will be applicable to subsequent stages of the alignment development process, to optimize the alignments as new constraints are defined through the further consultation and environmental analysis phases, where more detailed and accurate data is obtained.

“The Authority would not have had the time or resources to identify and evaluate the broad range of potential options/variations (literally millions) through these mountain crossings and achieve this level of confidence through any other means.”
California High Speed Rail Authority

Project Benefits

  • Identified construction cost savings
  • Found the most viable options for infrastructure requirements while reducing environmental impact
  • Minimized tunnel length and capital costs