In recent decades pavement management optimization has been designed with the objective of minimizing user and agency life-cycle costs. However, pavement management decisions also have significant impacts on life-cycle energy use and environmental emissions from pavement management activity and user vehicles. This study expands beyond optimizing pavement rehabilitation strategy for minimization of life-cycle costs to also include greenhouse gas (GHG) emissions. We extend previous work on the single-facility, continuous-state, continuous-time optimal pavement resurfacing problem to solve the multi-criteria optimization problem with the two objectives of minimizing costs and GHG emissions.

The balance between the potentially two different optimal rehabilitation policies is found through the use of a Pareto frontier, which exists in the span between the cost- and emission- optimal strategies. The Pareto frontier provides decision makers with the dollars per tonne of GHG emissions saved due to a change in rehabilitation strategy. Results using California data indicate that there is a tradeoff between costs and emissions when developing a pavement resurfacing strategy, providing a range of GHG emissions reduction cost-effectiveness options.

Case studies for a two-lane arterial and a ten-lane major highway in California are presented, where traditional hot-mix asphalt overlays are applied. The 2011 case studies are particular to California by traffic loadings and pavement durability. However, the user and agency emission and cost estimations are based on national data. Thus, generalizing the case study results should be subject to these caveats. An ordinary medium-volume metropolitan state-designed road and an extremely heavily traveled highway bearing commuters into and from San Francisco are optimized as representative situations.

Results for a one-kilometer segment of Interstate 80, in Berkeley California, with ten lanes and 273,000 light-duty vehicles and 13,100 heavy-duty vehicles per day, indicate that the life-cycle cost minimum occurs when asphalt overlays are applied every 15 years or equivalently when the pavement roughness reaches an international roughness index (IRI) of 2.7 m/km. Coincidentally, this is the same roughness Caltrans uses to decide when to apply an overlay for the state's roads. However, where any of the conditions or characteristics for any pavement segments are different, the coincidence may cease to exist. The minimum life-cycle cost at this optimal pavement rehabilitation strategy is approximately $490,000 per kilometer per year, at which point resurfacing activity and user vehicles would emit approximately 220 tonnes of CO2 equivalents per kilometer per year. The GHG emissions minimum corresponds to an overlay interval of 22 years or the equivalent threshold roughness IRI of 3.4 m/km. The minimum GHG emissions (user emissions plus agency emissions) are approximately 200 tonnes of CO2 equivalents per kilometer per year, with life-cycle costs (user costs plus agency costs) at approximately $520,000 per kilometer per year. Agency and user emission (and cost) estimates each change in opposing directions when overlay intervals change. Thus, when each of the like agency and user attributes are added together, a minimum is guaranteed to exist.

Any pavement rehabilitation strategy that makes use of overlay intervals outside of this sub-interval defined by the life-cycle cost and GHG emissions optima are trivial in that any strategy change designed to reduce costs also reduces emissions. However, inside this special sub-interval, any change in strategy that reduces costs will increase emissions and vice versa. Thus, this special sub-interval constitutes a Pareto frontier of optimal solutions where tradeoffs are associated with each change. For example, if Caltrans is currently operating at the life-cycle cost minimum by applying an overlay interval every 15 years but decides to reduce emissions by changing the interval to every 18 years, there will be a reduction in emissions. However, it will come at a total life-cycle cost of approximately $500 per tonne of CO2 equivalents. Of course different pavement rehabilitation strategy changes will present different cost-effectiveness ratios. If the change spans points outside the Pareto frontier, the costs may be minimal or even negative. However, within the Pareto frontier, attempts to save even more emissions will increase costs per unit of CO2 equivalents saved.

If a market value for CO2 exists, then a unique optimal pavement rehabilitation strategy is defined. On the Pareto frontier is every possible market value as the negative of the slope of the tangent line to each point on the curve represents a market value starting with zero dollars per tonne of emissions (cost minimum) to infinite dollars per tonne of emissions (emissions minimum).

Results for a two-lane arterial road segment, also in Berkeley, which has only 25,000 light-duty vehicles and 480 heavy-duty vehicles per day, indicate that similar pavement rehabilitation strategy overlay intervals are optimal. For the life-cycle cost minimum, a 16-year overlay interval is optimal, which corresponds to a threshold roughness IRI of 2.1 m/km. For the GHG emissions minimum, an overlay interval of 25 years and its associated threshold roughness IRI of 2.5 m/km are optimal. Although the overlay intervals are not that different from the larger ten-lane interstate highway case, the threshold roughness values are more favorable in the two-lane case. The life-cycle cost minimum occurs at approximately $80,000 per kilometer per year and is associated with approximately 51 tonnes of CO2 equivalents per kilometer per year. The GHG emissions minimum occurs at approximately 47 tonnes of CO2 equivalents per kilometer per year and is associated with approximately $86,000 per kilometer per year.

A sensitivity analysis on model input parameters revealed which parameters required the best accuracy and shed light on policy decisions. Pavement deterioration rate, within a 20% variation, had a relatively little effect on outcomes. This indicates that uncertainty around the pavement deterioration rate is not very important. However, a small change in vehicle miles traveled had a large effect on outcomes. Other results highlighted the contrast between strategy decisions for various pavement and vehicle technologies. For example, it is found that, in both case studies, improving vehicle fleet fuel economy will save total (tailpipe plus pavement) emissions. The two-lane case showed a larger percentage of relative reduction in emissions but the ten-lane case was found to have a larger total reduction in emissions. However, an improved fuel economy for the vehicle fleets means that the effect of roughness on fuel consumption is less. Thus, the GHG emissions associated with pavement management become a larger share of the total emissions. This means that at the emissions optimal, the pavements are allowed to become rougher before being rehabilitated again. Thus, to counteract the expected fuel economy improvements of the future, the use of new technologies that reduce emissions associated with pavement overlay activity, but also reduce roughness at optimality, is paramount. For the same reason, technologies that provide more durable pavements are also encouraged.

Carsharing has grown considerably in North America during the past decade and has flourished within metropolitan regions across the United States and Canada. The result has been a new transportation landscape, which offers urban residents an alternative to automobility without car ownership. As carsharing has expanded, there has been a growing demand to understand its environmental impacts. This paper presents the results of a North American carsharing member survey (N = 6,281). The authors establish a “before-and-after” analytical design with a focus on carsharing’s impacts on household vehicle holdings and the aggregate vehicle population. The results show that carsharing members reduce their vehicle holdings to a degree that is statistically significant. The average vehicles per household of the sample drops from 0.47 to 0.24. Most of this shift constitutes one-car households becoming carless. The average fuel economy of carsharing vehicles used most often by respondents is 10 miles per gallon (mpg) more efficient than the average vehicle shed by respondents. The median age of vehicles shed by carsharing households is 11 years, but the distribution covers a considerable range. An aggregate analysis suggests that carsharing has taken between 90,000 to 130,000 vehicles off the road. This equates to 9 to 13 vehicles (including shed and postponed auto purchases) for each carsharing vehicle.

This study examines the relative economics of electric vehicle operation in the context of current electricity rates in specific utility service territories. The authors examined 14 utility territories offering electric vehicle (EV) rates, focusing on California but also including other regions of the United States. The consumer costs of EV charging were examined in comparison with gasoline price data, geographic location, and during three highly variable gasoline price periods of July 2008, January 2009, and July 2009. In a switch from a conventional 23 mile per gallon (10.2 liters/100 kilometers) vehicle to a 300 watt-hours/mile electric vehicle driven 10,000 miles (16,100 km) per year, the study finds that savings in fuel costs ranged from approximately $100US to $1,800US annually, with considerable geographic variation and with higher-end values mostly in Summer 2008 when gasoline prices were relatively high. Charging off-peak instead of during peak periods saves an average of only a few hundred dollars US per year, rendering the incentive to charge off-peak a relatively small one except perhaps during some summer months when the on-peak prices are especially high. Gasoline price variances have a larger effect and switching from a low fuel economy conventional vehicle to the reference EV (compared with a switch from an already efficient vehicle) presents the highest savings level. The West and Midwest are generally the most favorable regions for EV economics, when EV charging rates and gasoline prices are considered together.

Over the last several decades, hydrogen fuel cell vehicles (FCVs) have emerged as a zero tailpipe-emission alternative to the battery electric vehicle (EV). To address questions about consumer reaction to FCVs, this report presents the results of a “ride-and-drive” clinic series (n=182) held in 2007 with a Mercedes-Benz A-Class “F-Cell” hydrogen FCV. The clinic evaluated participant reactions to driving and riding in an FCV, as well as vehicle refueling. Pre-and post clinic surveys assessed consumer response. More than 80% left with a positive overall impression of hydrogen. The majority expressed a willingness to travel five to ten minutes to find a hydrogen station. More than 90% of participants would consider an FCV driving range of 300 miles (480 kilometers) to be acceptable. Stated willingness-to-pay preferences were explored. The results show that short-term exposure can improve consumer perceptions of hydrogen performance and safety among people who are the more likely early adopters.