UC Davis Institute of Transportation Studies

Route 5 near the Florin Road overcrossing (PM 17.2/17.9) in Sacramento County is one of the eight quiet pavement test sections where traffic noise measurements are being conducted by the Caltrans Division of Environmental Analysis Team. This section is a rubberized asphalt concrete open graded (RAC-O) overlay of PCC built in summer 2004.

According to a slide in a PowerPoint presentation prepared by Caltrans Environmental (Figure 1), noise measurements were conducted on the section by Caltrans Environmental between approximately Station 55+40 and Station 60+80 on the southbound lanes and between Station 54+40 and Station 59+60 on the northbound lanes. According to the presentation sent to the Pavement Research Center (PRC) by Caltrans Environmental (Figure 1), both the northbound and southbound directions were divided into three segments of roughly equal lengths (exact stationing of measurements cannot be read from the presentation) and noise levels were obtained for each segment. The total distance over which noise measurements were made for each direction, as approximately read from the presentation, are shown in Figure 2 against the total length of the project. Measurements were repeated three times for each segment to account for measurement errors. According to the presentation, the segments are separated by gaps.

According to the noise levels reported by Caltrans Environmental, noise performance differences exist within the southbound segments as well as between the northbound and southbound directions, though the mix designs of all the segments were the same. Caltrans Environmental reported the following results:

* On the northbound direction, the variation among segments was as small as the difference between run-to-to run. * On the southbound direction, run-to-run differences for each sample segment were smaller than the differences between the segments, indicating that differences were related to variation in the pavement condition of each segment rather than measurement techniques. * Over the project, as much as 3.5-dB variation in noise levels was measured for averages of six different pavement sections. Noise performance differences were significant at lower frequencies (1250 Hz and below). * The overall noise level of the northbound pavement is on average higher than southbound.

PRC evaluation of the results presented in the Caltrans Environmental presentation (Figures 3 and 4) indicate that the maximum difference within the southbound direction is about 3.5 dB, and the difference between the average north and southbound directions is less than 1.5 dB. Verbal communication with Caltrans Environmental indicated that all sound intensity measurements were taken in the outside lane.

On January 26, 2005, a team from the PRC performed a field survey of the project with the following objectives:

* Investigate visual differences in surface condition between northbound and southbound directions * Investigate visual differences in surface condition of different segments of southbound direction where the noise measurements were taken, * Locate any distresses on both directions

It was raining during the visit, which enabled the water handling ability of the pavement to be observed.