VMT Analysis of Auxiliary Lanes

The California Department of Transportation (Caltrans) Highway Design Manual defines an auxiliary lane as follows:

62.1 Geometric Cross Section (1) Lane. a) Auxiliary Lane--The portion of the roadway for weaving, truck climbing, speed change, or for other purposes supplementary to through movement.

  

Auxiliary lanes can include a range of design features, such as acceleration and deceleration lanes, and connections between successive entrance/exit ramps that may need to be considered in a VMT analysis. The Governor’s Office of Planning and Research (OPR), State of California, Technical Advisory on Evaluating Transportation Impacts in CEQA (December 2018) addressed auxiliary lanes as follows:

F. Considering the Effects of Transportation Projects on Vehicle Travel

Projects that would not likely lead to a substantial or measurable increase in vehicle travel, and therefore generally should not require an induced travel analysis, include:

Addition of an auxiliary lane of less than one mile in length designed to improve roadway safety.

  

This OPR guidance was carried over into the Caltrans Transportation Analysis Under CEQA (September 2020). As more projects have implemented this guidance, it has become apparent that some clarifications would be helpful to project development teams. Two issues are addressed below.

 

Extension of an existing auxiliary lane

 

In reviewing the information considered in providing the original guidance in the OPR Technical Advisory, the purpose of the one- mile threshold was to require the lead agency to consider the potential for induced travel when a project adds an auxiliary lane not primarily designed to improve roadway safety, as described above. Therefore, extensions of existing auxiliary lanes less than one mile that result in auxiliary lanes of more than one mile should review the following guidance, also included in Section 5.1.1 of the Caltrans Transportation Analysis Under CEQA:

When concluding that a particular project may be screened out from further analysis, the practitioner should review and fully document the rationale supporting the conclusion that the particular project would not likely lead to a measurable and substantial increase in VMT.

 

Analysis of a multiple auxiliary lanes in the same corridor:

 

The addition of multiple new auxiliary lanes in the same corridor should be carefully assessed on a case-by-case basis. The OPR December 2018 Technical Advisory included the following guidance:

Whether adopting a threshold of significance, or evaluating transportation impacts on a case-by-case basis, a lead agency should ensure that the analysis addresses:

Direct, indirect and cumulative effects of the transportation project (CEQA Guidelines, § 15130.)

 

Cumulative impacts refer to two or more individual effects which, when combined together, are considerable or which compound or increase other environmental impacts. The individual effects may be changes resulting from a single project or several separate projects. The cumulative impact  is the change in the environment which results from the incremental impact of the project when added to other closely related past, present and reasonably foreseeable probable future projects. Cumulative impacts can result from individually minor but collectively significant projects taking place over a period of time (Publ. Res. Code, § 15355; CEQA Guidelines § 15064, subd. (h); CEQA Guidelines, § 15130). A project or series of projects that add a series of auxiliary lanes in the same corridor should evaluate potential cumulative impacts. If the effect is cumulatively considerable, the consideration of alternatives or mitigation is required.

 

For example, it must be determined whether the series of auxiliary lanes are collectively influencing capacity or otherwise potentially significantly inducing travel in the corridor, or alternatively whether each of the auxiliary lanes are operating independently and only addressing localized operational issues. If the conclusion is that each auxiliary lane is independent, and each are under one mile in length, an induced travel analysis generally should not be required. If on the other hand it is determined that the series of auxiliary lanes would collectively create a significant increase in traffic capacity in the corridor, an induced travel analysis would be required.

 

The consideration of reasonably foreseeable probable future projects could include anticipated actions leading to connections among otherwise independent auxiliary lanes (i.e., connecting two auxiliary lanes through an interchange by widening or lengthening a bridge structure). If a project proposes to add an auxiliary lane that “connects” otherwise independent auxiliary lanes, that project should consider whether an induced travel analysis is appropriate, despite any previous exemption determinations in the corridor. In all cases, substantial evidence would be required to justify the conclusion and the decision whether to perform an induced travel analysis.