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 considered this guidance, it has become apparent that some clarifications would be helpful to project development teams. Two issues are addressed here:

Extension of an existing auxiliary lane:

In reviewing the information considered in providing the original guidance in the OPR Technical Advisory, the limit of one mile was to prevent the advancement of a project that went beyond the normal function of an auxiliary lane without considering the potential for induced travel. Therefore, any extension of an existing auxiliary lane less than one mile that results in an auxiliary lane 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:

This is a situation that needs to be carefully assessed on a case-by-case basis. The OPR December 2018 Technical Advisory also 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 considered together, are considerable or which compound or increase other environmental impacts.  The individual effects may be changes resulting from a single project or a number of separate projects.  The cumulative impact from several projects is the change in the environment which results from the incremental impact of the project when added to other close 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.  (Public Resources Code § 15355; Guidelines §15064, subd. (h) and §15130.)

The issue of cumulative effects is relevant to the the evaluation of the effects caused by a series of auxiliary lanes in the same corridor.  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 truly 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. In either case, substantial evidence would be required to justify the conclusion and the decision whether to perform an induced travel analysis.