Port-of-Entry Emissions Inventory for the El Paso Region

Models show connections between wait times and emissions rates at Zaragoza Bridge

What’s the Problem?

When vehicles are idling in heavy or standstill traffic congestion, the resulting emission pollutants impact air quality significantly. El Paso region border ports of entry (POEs) are of particular concern due to the north- and southbound commercial and passenger vehicle queues and long wait times at inspection stations. Texas’ Rider 8 program assists agencies by supporting local air quality planning efforts to meet federal and state attainment standards. This involves measuring air quality and developing solutions to improve it. To keep traffic moving smoothly and efficiently through the POEs, as well as continue improving air quality in these areas, researchers need to assist agencies in determining which traffic management solutions would reduce idling and wait times, and then compare air quality before and after solutions are implemented. Use of computer modeling simulation is an important and cost-effective development and monitoring tool for these efforts.

How Was the Study Done?

TTI researchers used the TransModeler® software platform to develop a detailed, simulation-based model of the Ysleta-Zaragoza POE for commercial and passenger vehicles. Including north- and southbound traffic flows over a 24-hour period, researchers modeled eight scenarios that included reduction in both wait time and the number of inspection booths open for use. Output from the simulation model then became input for MOVES, an air quality modeling system that estimates mobile source emissions for criteria air pollutants, greenhouse gases, and air toxins. A base model, also known as a do-nothing model, was used as a basis of comparison.

Study Findings

Results of the scenario modeling showed that passenger cars benefited most from the strategies tested. For commercial vehicles, however, air quality improved very little when reducing wait times.

For passenger cars, decreasing wait time by 15 percent had a double-digit percentage change in all emissions. When wait time was reduced 25 percent:

• Carbon monoxide decreased 30 percent
• Carbon dioxide decreased 32 percent
• Nitrogen oxide decreased 25 percent

However, when this 25 percent wait time reduction was coupled with a 75 percent reduction in the number of inspection booths open, there was a dis-benefit to overall air quality:

• Carbon dioxide increased 26 percent
• Nitrogen oxide increased 19 percent
• Particulate matter increased 15 percent

For commercial vehicles, with a 20 percent reduction in wait time, particulate matter was only reduced by less than 1 percent when compared to the do-nothing scenario. It was not until wait time was decreased by at least 25 percent that emissions reductions were achieved for almost all emission types. When wait time was reduced and was modeled in conjunction with various numbers of inspection booths available, emissions for passenger cars increased and had only a negligible decrease for freight vehicles.

Benefits of this Research

This study provided insights into how various combinations of reduction in wait time and open inspection booths can affect emissions differently for passenger and commercial vehicles. These findings will assist the El Paso region in further refining targeted solutions to traffic congestion and air quality issues at specific POE locations along the border, depending upon passenger and commercial traffic counts, types of vehicle fleet mixes, and number of inspection booths available.

Details of the study methodology and findings can be found in the full report.