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31 <br />iteratively adjusted to replicate MOBII,E6.2's national classification default within the analysis <br />area. The final numbers reflect the change in the mix (i.e. increase in the number of SUVs and <br />pick-ups) for each yeaz using MOBII,E6.2 projection and variation of mix across the different <br />road type using NC data. This reflects 16 vehicle classes per road type. <br />4.1.3 Vehicle Age Distributiions <br />The vehicle age distribution is based on the North Carolina Department of Motor Vehicles' 2007 <br />(DMV) registration records for the in-use fleet in the Triangle azea. DMV provided the <br />information. The data was modified and arranged to comply with MOBII.E6.2 <br />4.2 Transaortation Control Measures <br />The North Cazolina State Implementation Plan lists no transportation control measures pertaining <br />to the Triangle. <br />4.3 Estimation of Vehicle Starts <br />A component of the emissions rates for each functional class is an estimate of the start-based <br />emissions. This rate is based on an assumed number~of starts per vehicle and is added to running <br />emissions to produce a single rate to apply to vehicle miles traveled. Mobile 6 defaults are 7.28 <br />starts for passenger cars and 8.06 starts for light duty trucks. However, the use of default rates isn't <br />the best practice for heavily urbanized areas with an updated Travel Demand Model. Area-specific <br />rates were calculated by dividing the total number of trips from the travel demand model by the total <br />number of registered vehicles. Appendix G contains additional information. This methodology has <br />been previously endorsed by USEPA and used in prior conformity analysis in the Triangle. <br />4.4 Off-model Analysis <br />The Triangle Regional Model (TRM) does not include algorithms that can calculate the effects on <br />VMT and speeds (and hence air quality) of certain transportation related activities designed to <br />influence people's travel modes or affect the supply of or demand for transportation services. <br />Examples of such activities that currently exist in the Triangle include: <br />• Transportation Demand Management (TDM) programs such as the Triangle Best <br />Workplaces for Commuters program and the SmartCommute@RTP program which cover <br />approximately 10°Io of the region's workforce, <br />• Land use strategies, such as compact, mixed-use, pedestrian- and transit-oriented <br />development and design initiatives, over and above those reflected in the Traffic Analysis <br />Zone (TAZ) socioeconomic data, <br />• Commuter Services Programs operated by the Triangle Transit Authority, such as the <br />Guazanteed Ride Home program, rideshaze matching software and the vanpool program, and <br />• Incident management programs conducted on the region's Interstate highways and other <br />freeways in Wake and Durham Counties, including surveillance cameras, the Motorist <br />Assistance Patrols, and traveler information activities. <br />In order to accurately account for the impacts of such activities, they are reflected through "off- <br />model" analyses. Although these and other programs are suitable for off-model analysis, this <br />conformity determination included off-model analysis only for the last of these listed activities, <br />23 <br />