Robert Sperry

Comparison of on-road emissions for hybrid and regular transit buses

Hybrid technology offers an attractive option for transit buses, since it has the potential to significantly reduce operating costs for transit agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Laboratory tests have indicated that hybrid transit buses can have significantly lower emissions compared with conventional transit buses. However, the number of studies is limited and laboratory tests may not represent actual driving conditions, since in-use vehicle operation differs from laboratory test cycles. This paper describes an on-road evaluation of in-use emission differences between hybrid-electric and conventional transit buses for the Ames, Iowa transit authority, CyRide. Emissions were collected on-road using a portable emissions monitoring system (PEMS) for three hybrid and two control buses. Emissions were collected for at least one operating bus day. Each bus was evaluated over the same route pattern, which utilizes the same driver. The number of passengers embarking or disembarking at each stop was collected by an on-board data collector so that passenger load could be included. Vehicle emissions are correlated to engine load demand, which is a function of factors such as vehicle load, speed, and acceleration. PEMS data are provided second by second and vehicle-specific power (VSP) was calculated for each row of data. Instantaneous data were stratified into the defined VSP bins and then average modal emission rates and standard errors were calculated for each bus for each pollutant. Pollutants were then compared by bus type. Carbon dioxide, carbon monoxide, and hydrocarbon emissions were higher for the regular buses across most VSP bins than for the hybrid buses. Nitrogen oxide emissions were unexpectedly higher for the hybrid buses than for the control buses. Implications: The main reason agencies consider hybrid transit vehicles is fuel savings and reduced emissions. Hybrid electric buses offer an attractive option and have the potential to significantly reduce operating costs and emissions for transit agencies. However, purchase of hybrid buses cost 50–70% more than regular buses. As a result, agencies require more quantitative information about the on-road costs and benefits of hybrid buses. This study assessed on-road emissions for in-use transit buses. The resulting information can be used by transit agencies in assessing the likely emission reduction benefits for hybrid buses.

Infrastructure impacts of Iowa's renewable energy.

This paper investigates the physical and fiscal impacts of Iowas existing biofuel plants and wind power industries. A four-county cluster in northern Iowa and a two-county cluster in southern Iowa were identified through a local agency survey as having a large number of diverse facilities and were selected for analysis of traffic and physical impact. The large-truck traffic patterns on Iowas secondary and local roads from 2002 to 2008 were analyzed and associated with the pavement condition and county maintenance expenditures. A trend of increased maintenance costs in the year after a biofuel plant became operational as well as during the construction period was observed. Large-truck traffic also increased dramatically during the construction period and then dropped after the plant became operational, but not to the levels before the plants construction. The major road damage associated with wind farms occurred during construction activities and predominantly on gravel roads. Face-to-face interviews with county engineers were conducted to validate the observed trends and discuss the limitations of the data. Finally, with an expanded sample of 24 counties, one-way panel data regression models were developed to estimate pavement condition and maintenance costs as a function of vehicle miles traveled, plant capacity and years of operation, corn and soybean production, and soil and environmental conditions.

Field application and assessment of the safety edge

Pavement edge drop-off can be a serious safety concern when a vehicle leaves the paved roadway surface and encounters a significant difference in vertical elevation between the paved roadway and the adjacent unpaved shoulder. Edge drop-offs are potential safety hazards because scrubbing between the pavement edge and tire can result in loss of control. FHWA developed the Safety Edge on the basis of research results that indicated a sloped pavement edge surface could be more easily traversed by a vehicle leaving its lane and attempting to remount the pavement edge. The Safety Edge is a design feature that creates an approximate 30° fillet along the outside edge of the paved section of a roadway. Although a number of benefits have been attributed to the Safety Edge, agencies in Iowa were slow to adopt it. To accelerate use of the Safety Edge, the research team marketed and monitored it in Iowa during the 2010 construction season. This project provided the opportunity to evaluate the Safety Edge as well as summarize lessons learned from agencies and contractors. Evaluation of the Safety Edge included assessment of the consistency of slope application, identification of common problems during construction, measurement of the density of the Safety Edge, and computation of the approximate additional material needed to construct the Safety Edge. The team also measured drop-off formation along previously constructed Safety Edge sites and compared this with control sites to assess any difference in occurrence.