The CAA identifies actions (transportation control measures or TCMs) that may be taken to reduce emissions from mobile sources9. In addition, there are other measures such as vehicle controls, fuel-based standards, and inspection and maintenance programs that may also help areas reduce mobile source emissions. While some of the measures are not the responsibility of State and local transportation officials, it is beneficial for officials to be familiar with on-road motor vehicle control programs implemented by other public agencies (e.g., motor vehicle departments, environmental agencies), automobile manufacturers and fuel suppliers. Having an understanding of the costs and benefits of all available options to achieve emission reductions is useful to officials in advance of being asked to make decisions on specific strategies for implementation.
Options to control and reduce emissions from motor vehicles comes under the category of TCMs. Implementation of these measures is typically within the purview of transportation agencies, and TCMs are usually funded with FHWA/FTA or State and local transportation funds. The emission reduction potential of conventional TCMs, such as ridesharing and bicycling programs is not likely to be as substantial as the technology-based transportation measures discussed above. Nevertheless, TCMs can be useful in reducing congestion and may be needed in some areas in order to demonstrate attainment of the NAAQS. TCMs such as expanded transit services can also provide and enhance travel options and increase travel choices.
The CAA requires that in ozone nonattainment areas classified as severe or extreme, the State must identify and adopt specific transportation control strategies and TCMs to offset any projected growth in emissions from growth in vehicle miles traveled. States and MPOs should consider the CAA list of TCMs (Section 108(F)(1)(A)) for strategies they might include in the SIP. These 16 TCMs (with the exception of programs to encourage the removal of pre-1980 vehicles) are eligible for Congestion Mitigation and Air Quality Improvement (CMAQ) Program funding. Below is the list of TCMs included in the CAA. There is overlap between some of the measures and the descriptions listed illustrate types of projects that might be considered in nonattainment areas to reduce mobile source emissions or to increase overall vehicle occupancy.
9 CAA Section 108(f)
In addition to conventional TCMs, work is underway in nonattainment areas to explore options to reduce mobile source emissions using market-based TCMs such as road pricing, congestion pricing, vehicle miles of travel (VMT) fees, and parking pricing. These mechanisms can be relatively cost-effective and can be designed to impact vehicles at either certain times of the day (e.g., peak-period pricing), or at all times. In addition, these measures in combination with traditional TCMs have the potential to address other public policy objectives such as congestion reduction and energy conservation.
In many areas public acceptance of market-based TCMs has been slow due to practical and political considerations. For example, implementation of market-based measures may require State legislation (e.g., congestion pricing) or a voter referendum. Therefore, regardless of the potential merits and cost-effectiveness of these measures, the implementation of market-based TCMs is likely to occur gradually.