Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration
Office of Planning, Environment, & Realty (HEP)

Detailed Monitoring Protocol

1.0 Introduction

To view PDF files, you need the Acrobat® Reader®.

The Federal Highway Administration (FHWA) was involved in a legal action concerning the U.S. 95 Widening Project in Las Vegas, Nevada. In that action, the Sierra Club challenged FHWA's and the Nevada Department of Transportation's (DOT) assessment, presented in the National Environmental Policy Act (NEPA) environmental document, of impacts of mobile source air toxics (MSATs) from the proposed project. To resolve the situation, FHWA entered into a Settlement Agreement with Nevada DOT and the Sierra Club. The Settlement Agreement is provided in Appendix A of this Protocol.

In this Settlement Agreement, FHWA agreed to undertake a research effort to characterize the impact and behavior of particulate matter with aerodynamic diameter less than 2.5 microns (PM2.5) and MSATs near highways. As part of this Agreement, FHWA agreed to develop a "detailed protocol" outlining a uniform approach to conducting all studies for evaluating mobile source contributions to air toxic compounds and PM2.5 and their dispersion patterns in up to five highway locations. In addition, FHWA was required under the Agreement to prioritize a list of potential study locations, or if necessary, prepare to conduct its own study at one highway location. The Agreement is intended to promote field measurement of the contribution of mobile sources to PM2.5 and MSATs, but is not intended to characterize the potential human health impacts of public exposure to MSATs or PM2.5.

1.2 Monitoring Objective

The objective of the studies to be conducted under this Protocol is to determine MSAT concentrations and variations in concentrations as a function of distance from the highway and to establish relationships between MSAT concentrations as related to highway traffic flows including traffic count, vehicle types, and speed; and meteorological conditions such as wind speed and wind direction. To meet this objective, up to five year-long studies may be performed at different selected sites.

As an example of the dispersion of pollutants away from a highway, Figure 1-1 shows the results of a recent study in which the concentration of airborne particles was characterized as a function of distance from a highway (Freeway 405 in Los Angeles).1 These results suggest that the vast majority of dispersion for occurs within 300 meters of the highway, and that the initial pollutant concentration varies depending on the season.

This figure shows an example of pollutant dispersion as a function of distance from a highway. Two plots are shown illustrating an exponential decay in pollutant concentration as a function of distance for the summer and winter months for a highway in Southern California. By approximately 300 meters from the roadway the pollutant concentrations have decayed by approximately 90%.
Figure 1. Example of Pollutant Dispersion as a Function of Distance from a Highway.

It is expected that the studies conducted under this Protocol will generate data that can be used to characterize similar types of dispersion patterns as well as relationships between various traffic and meteorological parameters and the concentrations of MSATs.

1.3 Purpose of Document

The purpose of this Detailed Protocol is to specify how to conduct the field studies called for by the Settlement Agreement, i.e., addressing the impact of mobile sources on PM2.5 and MSAT concentrations near highly traveled roadways. This Protocol has been developed to address all aspects of the field studies called for in the Settlement Agreement, including selection of the study location; placement and setup of sampling sites; application of appropriate sampling and analysis methods, including monitoring of surrogate or indicator compounds; coordination of chemical sampling with meteorological and traffic monitoring over defined sampling periods and study durations; quality assurance activities; and analysis of the study data. Furthermore, the Protocol defines and recommends the logistical process to be followed when more than one such field study is to be carried out, such that simultaneous or sequential studies can benefit from concurrent or previous efforts.

The primary goal of this Protocol is to provide understandable and readily implementable procedures and guidance that can be used by any organization carrying out such a mobile source field study. It is expected that the multiple field studies required under the Settlement Agreement may be carried out by the FHWA or its contractor(s), or by state DOT's or their contractors. Consequently, the Protocol is sufficiently detailed but widely applicable, so that field studies carried out by diverse agencies in widely different parts of the United States will have a consistent scope and produce data of comparable breadth and quality.

1.4 Associated Settlement Requirements

Although not directly a part of the monitoring studies to be conducted under this Protocol, the Settlement Agreement calls for the development of an emission inventory from data collected during these studies. Additional information regarding emission inventory development is provided in Section 7.3.

Updated: 10/20/2015
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000

All Federal Highway Administration (FHWA) information technology systems will be unavailable, Friday, December 2, at 10:00 p.m. to Sunday, December 04, at 11:59 p.m., EDT, while work is being performed on the network. During that time, users will not be able to access any FHWA systems.

If you have any questions or problems, please contact the 5-Help Service Center @ (866) 466-5221 or