Recent concern about carbon monoxide exposure to the commuter population prompted the U.S. Environmental Protection Agency to conduct a five-day field project to assess the CO exposure to Los Angeles commuters. The purpose of this report is to document the field project and to provide the data collected during the project to the public. The data collected during this project includes measurements of interior carbon monoxide, exterior carbon monoxide and vehicle speed for three vehicles traveling typical commute routes during the morning and evening peak traffic periods. In addition, hourly average CO measurements were taken from eight South Coastal Air Quality Management District fixed-site monitoring stations and six California Transportation Agency vans in the proximity of the commuter routes.