The stretch of I-15 south of St. George was the leading traffic gainer on major highways in southern Utah during the past 12 months, surpassing an average daily traffic of 11,000 vehicles for the first time.

U.S. 89 was alone in traffic declines - and that was only at one reporting station in Piute County. All other interstate, U.S. and state highways registered increases.The decrease on U.S. 89 north of Marysvale was only 1.9 percent during the 12 months ending March 31, according to latest figures from the Utah Department of Transportation. That station recorded an average of 1,267 vehicles daily.

Several additional reporting stations have been established by UDOT, so comparative traffic figures are not available at those locations. During the first three months of the year, an average of 4,104 vehicles daily was recorded at a new station south of Nephi on I-15 while 5,400 passed a recorder on that same highway north of Paragonah, Iron County.

Other new stations and average daily vehicles in the first quarter of 1991 are U.S. 89 in Salina, Sevier County, 2,677; U.S. 89 south of Circleville, Piute County, 742; U.S. 191 south of Bluff, San Juan County, 1,115; and U.S. 6 northwest of Price, 6,807.

Interstate highway stations, with the percentages of increases and average daily traffic during the last year, are I-15 south of St. George, 10.7, 11,170; I-15 south of Leeds, Washington County, 2.8, 9,313; I-15 north of Beaver, 8.0, 8,294; I-15 south of Scipio, Millard County, 6.6, 6,998; and I-70 northwest of Green River, Emery County, 0.7, 2,948.

U.S. highways and traffic increase figures are U.S. 6 west of Helper, Carbon County, 7.7 percent, 4,732 average daily vehicles; U.S. 89 east of Kanab, 2.4, 1,500; U.S. 6 northwest of Green River, 5.9, 2,859; U.S. 191 north of Monticello, San Juan County, 3.8, 2,760; and U.S. 191 near Moab, 9.5, 3,480.

State highways and traffic recordings include U-95 south of Hanksville, Wayne County, 0.4, 522; U-14 east of Cedar City, 2.2, 1,452; U-9 west of Hurricane, Washington County, 3.8, 6,078; and U-21 west of Beaver, 2.3, 776.