Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
United States Department of Transportation (USDOT) study predicts that vehicle-miles traveled
(VMT) will grow between 1.91% and 2.26% annually during the next two decades—leading to a
62% total increase from 2001 to 2025. Other key factors that may influence travel and the
opportunities to manage it include:
• Suburban seniors aging in place
• Increasing performance capabilities of seniors—and thus more elderly drivers
• Increasing percentage of non-English speaking population
• Flattening of the growth in household income
• Increasing motor-vehicle ownership
• Increasing level of education
• Increasing re-gentrification and densification of central cities; continued growth at the
low-density edge of cities
• Increasing number of multi-worker families
• Increasing prevalence of internet usage and telecommuting
• Increasing transit usage
• Decreasing average vehicle size
• Increasing level of ride sharing (increasing average vehicle occupancy)
ENVIRONMENT AND CLIMATE CHANGE
The U.S. Environmental Protection Agency (EPA) website states: “Scientists are certain that
human activities are changing the composition of the atmosphere, and that increasing the
concentration of greenhouse gases will change the planet's climate.” One of the causes of climate
change is the increase in CO 2 emissions, with transportation contributing 24% of the total U.S.
greenhouse gases (GHG) in 2006. Furthermore, highway vehicles (passenger cars and trucks)
accounted for 79% of transportation CO 2 emissions in 2006. The growth in GHG emissions is
linked to the increase in VMT for the following vehicle categories, Figure 4.2:
• Light-duty: +39% (1990-2006)
• Heavy-duty: +58% (1990-2005)
• Aircraft: +69% (1990-2005)
TRENDS AFFECTING TRAVEL-TIME RELIABILITY Page 38