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Chapter 7. Conclusions

Now that MOVES2010 has been released, many transportation and air quality researchers are working to take advantage of MOVES's capability and flexibility using available local data, experiments measuring driving patterns, and by linking MOVES with models that simulate vehicle behavior. This project uses the capabilities of traffic microsimulation models to develop VSP profiles for some of the situations that project-level analyses are likely to be interested in using MOVES to evaluate. Profiles are available from this study for freeway on-ramps, freeway-to-freeway interchanges, freeway incidents, and signalized arterials as an alternative to using standard MOVES defaults. Expected users of these VSP profiles would be analysts who are interested in improving upon the standard MOVES defaults, but who do not have the means to use microsimulation models to develop such profiles themselves. The research work provides practitioners who are interested in using microsimulation output as input to MOVES with some case study examples of potential processes and associated challenges.

The study demonstrated that microsimulation can provide inputs in a form that can be used by the new generation of emissions models, in this case, the MOVES model. The linkage was made by producing operating mode distributions for network links with different geometric and operating characteristics from the detailed vehicle activity produced by microsimulation models. The study limited the number of links used in each geometric/operating scenario. However, the links were concentrated in and around bottleneck locations, which should be the focus of more intensive scrutiny because these are the locations where vehicle activity is the most variable due to traffic flow turbulence and queuing.

Under very severe congestion levels, the link limitation probably did not capture the full extent of queuing it most likely extended past the most upstream of the test links. To compensate for this, analysts can make an off-line determination of expected queue length and then assign the extra links the same operating mode distribution as links with queuing from the scenario tests.

Microsimulation models produce a file that has a speed and acceleration estimate for every vehicle in the network. This provides too many values for most modelers needs. In this study, since both speed and acceleration are available in the microsimulation output for every vehicle for every second of simulation, MOVES operating mode distributions based on VSP were computed instead. According to EPA's recent draft PM hot spot guidance, this is thought to be a much more accurate way of capturing driving cycle patterns where literally thousands of vehicles have their trajectories traced, as in simulations.

In modeling external truck trips to ports, the VMT distribution by roadway functional classification is important to pinpoint, because it provides an indication of the speed that trucks drive traveling to and from these ports. Emission rates vary by speed.

Using information from an example port, a number of emission control strategies that could be used to reduce emissions at ports were analyzed. The strategies evaluated included idling reduction, diesel retrofits, truck replacements, and freight diversion to rail. From these analyses it was found that:

1.         The idling reduction strategy provides significant CO, NOx, and PM emission reductions.
2.         MOVES passes through whatever the estimates of emission reductions are for a retrofit control technology and the penetration rate of that technology into the fleet.
3.         The estimated emission reductions for a truck replacement strategy were not as pronounced as for the other strategies, in part due to the short driving distances used in the evaluations.
4.         Emission differences between using default drive cycles and VSP profiles for the example emission control strategy analyses were small. This appears to be the result of extended idling emissions being a large portion of total port emissions and these off network sources are not affected by VSP profiles.

Similarly, this report also describes another set of MOVES files that can be used to model the unique conditions that occur at intermodal facilities and ports, capturing important activities such as idling, for the specific types of vehicles (trucks) used at these types of facilities.

Because MOVES2010 has been released less than one year, it is expected that considerable effort will be undertaken to develop MOVES inputs that take full advantage of MOVES abilities to estimate emissions by driving mode. Therefore, analysts that use the profiles provided as one of the products of this project should be aware of new opportunities to improve the information that they are using in project-level analysis.

Prior studies of port terminal attracted travel have focused mainly on truck origins and destinations. There is little or no information in the literature that provides measurements of trucks speed profiles as they travel to and from ports, or inside the port terminals. However, at least one research study is making such measurements, so transportation practitioners should be aware of, and make us of, the information available from such studies to improve their own emissions modeling work.

For example, there is ongoing research on truck travel nearby and inside port terminals at the Port of Houston. Preliminary information from this Port of Houston study contains speed and brake-horsepower by sequence profiles from portable emission measurement systems installed on trucks that traverse the Houston freeways that provide truck access to the Port of Houston. These profiles or similar ones developed for other areas can be matched with the VSP profiles provided in this study to determine the appropriate VSP profile for use in MOVES.

The Port of Houston profiles for inside-the-gate port activity are particularly useful for modeling truck behavior given the lack of information on such activity in the literature. The inside-the-port portable emission measurement systems measurements indicate that 69 percent of the time that trucks are at the port, they are idling. Preliminary information from this study was presented at the September 2010 EPA Emission Inventory Conference and can be found at www.epa.gov/ttn/chief.

Updated: 07/26/2011
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