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A. Remote sensing devices that constitute a roadside vehicle emissions monitoring system.

Q. What is remote sensing?

A. The measurement of exhaust emissions as a vehicle passes without interfering with or altering its progress. Infrared (IR) and ultraviolet (UV) light is directed across the road and passively reflected back to detectors that monitor light intensity at characteristic wavelengths. The amount of IR or UV light absorbed is translated into the exhaust concentration of the regulated pollutants of interest, carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and nitrogen oxides (NO).

Q. What are the benefits of remote sensing?

A. Speed - Individual vehicle emissions are measured in less than a second. Convenience - Emissions are measured unobtrusively as the vehicle passes by. Efficiency - Remote sensing can be used to screen vehicles on the road, supplementing traditional vehicle inspection programs. Cost - Supplementing traditional emissions testing at fixed facilities with on-road remote sensing can reduce the overall cost of a program. Effectiveness - Remote sensing is considered one of the best ways to evaluate I/M program performance.

Q. How long does it take to test a vehicle's emissions?

A. Background levels before the vehicle are subtracted from exhaust levels to compute the vehicle pollutant emissions. A digital image of the license plate is captured. The speed and acceleration are measured. All this data and other relevant information are recorded to complete the test in less than 1 second.

Q. Where can the equipment be used?

A. The AccuScanâ„¢ RSD can be positioned on a roadway that allows for a distance of 15 to 23 ft. (4 to 7 m) between the source detector module (SDM) and transfer mirror module (TMM) to monitor a single lane of traffic flowing in one direction. The ideal mode of operation for measurement is slight acceleration. This mode is often found at highway on-ramps with uphill grades and vehicle speeds between 35 and 45 mph.

Q. What gases does the AccuScanâ„¢ equipment test for?

A. The AccuScanâ„¢ 3000 measures all regulated criteria pollutants: CO, CO2, HC, and NO. The AccuScanâ„¢ 4000 measures these four and smoke. ESP is looking into including nitrogen dioxide (NO2) and sulphur dioxide (SO2) channels in the future.

Q. How long does it take to implement a remote sensing program?

A. This depends on the size, scope, and type of the program. For example, if the goal is a general motor vehicle fleet survey, with one or two AccuScanâ„¢ devices, the time from concept to launch can be very short (e.g., 2 months). If it is a long-term screening program covering a large fleet of vehicles with multiple AccuScanâ„¢ devices, the time will be longer (6 to 9 months), but this method is still faster than other vehicle emissions testing methods.

Q. How many vehicles can the AccuScanâ„¢ test annually?

A. Remote sensing measurements are weighted by vehicle miles traveled. The more often a vehicle is on the road, the more likely it will be tested by an RSD. In contrast, inspection program measurements are driven by registration renewals. ESP's experience in long-term continuous programs has been measurement of approximately 80% of the registered population when remote sensors are deployed for passive on-road measurement. Using active recruitment such as advertised car-care clinics may increase coverage. However, some registered vehicles travel too infrequently to be captured by a remote sensor.

Q. How many people are needed to operate the AccuScanâ„¢ equipment?

A. One trained person can operate the AccuScanâ„¢ equipment.

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May 2010 article/video on "Remote Sensing Could Exempt Cars From Emissions Test"


2009 Clean Air Conference Presentation: "Pre-screening and Evaluation of High Evaporative Emissions using RSD"(PDF 685 KB)by Jim Sidebottom, Colorado Department of Public Health and Environment

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