The evaluation of air quality benefits from implementing automatic vehicle identification (AVI) technology for electronic toll collection (ETC) has produced some positive results.

Located in Orlando, Florida, the Orlando-Orange County Expressway Authority (OOCEA) operates eleven mainline toll plazas. The busiest, the Holland East Toll Plaza, includes fourteen toll lanes. Nine of which are used for peak direction travel. A before-after study on the Express Pass (E-PASS) implementation of AVI based ETC at the toll plaza was conducted to evaluate the reduction in vehicle emissions. Specifically, the reductions in Carbon monoxide (CO), hydrocarbons (HC), and Nitrogen Oxides (NOx) were evaluated at the toll plaza.

When a vehicle with AVI transponder passes through the toll plaza, information about the toll transaction and balance remaining on the transponder is transmitted between the vehicle and a computer at the plaza. A message is then sent back to the vehicle, informing the driver that the toll is paid, balance information, etc.

Data for the before AVI study were collected from August 1994 to October 1994. Arrival, departure, and speed data was collected during the peak morning hour (7-8 AM) for fourteen days across all nine lanes in the westbound direction at the plaza.

The after study data were collected from July 1996 to August 1996 during the peak morning hour (7-8 AM) in the westbound direction for ten days. During this phase of the study, two dedicated lanes were configured for AVL/ETC operations and is the present status of the toll plaza.

In the period of time between "before" and "after" studies, the total average number of vehicles using the Holland East Toll Plaza during the peak hour increased by an average of 30 percent (1270 vehicles). Also, the average number of E-PASS users in the "after" study during the peak hour compared to the total volume is 40 percent. This was found by comparing the "after" study E-PASS users (2200 vehicles) to the total average volume (5504 vehicles). This is significant when considering that there were no E-PASS users in the "before" study.

Using the MOBILE5a emission model, and data collected, it was shown that even with the increased volumes at the Holland East Toll Plaza, vehicle emissions were reduced. An overall average reduction in Carbon Monoxide by 7.29 percent (5.21 kg) and HC by 7.19 percent (0.40 kg) resulted from the simulation. However, NOx increased by 33.77 percent (2.21 kg). This negative effect may be due to the fact that it is difficult to reduced CO and HC with increasing NOx.

To better evaluate the benefits of E-PASS on the reduction of emissions at the toll plaza, the same experiment was conducted examining two separate scenarios for a sensitivity analysis. One scenario compared values of the "before" study with values determined from a fictitious scenario of the present situation but having no E-PASS. The results from the fictitious scenario were compared with the present results of the "before" and "after" study comparison. The findings were that on the average, there was a reduction of 26.37 kg for CO and 1.79 kg for HC emissions for the present situation with E-PASS. NOx could still not be controlled and they increased by 0.24 kg because of increased speeds.

The other scenario was to hold the volumes of "after" study constant and compare the emissions results with and without E-PASS. CO decreased by 24.24 kg and HC decreased by 4.72 kg. NOx increased slightly by 0.46 kg, which was again attributed to an increase in speeds due to E-PASS.