Supervisors approve retention of South Mission Road 50 mph speed limit

The San Diego County Board of Supervisors voted to retain the 50 mph speed limit on South Mission Road between Pepper Tree Lane and State Route 76 while also recertifying the speed limit for radar enforcement.

The supervisors' 5-0 vote Feb. 14 covers 4.93 miles from 860 feet south of Pepper Tree Lane to State Route 76. When the county's Traffic Advisory Committee recommended retention and recertification of the speed limit Dec. 8 the TAC reviewed both the 2.04-mile section from 860 feet south of Pepper Tree Lane to Green Canyon Road and the 2.89-mile segment between Green Canyon Road and State Route 76.

"Safety on our roads is the priority, and after studying this area it is clear that a 50 mph radar-enforceable speed limit will help keep drivers safe," said Supervisor Bill Horn.

In order for a speed limit to be enforceable by radar, a speed survey must show that the speed limit is within an adjacent 5 mph increment to the 85th percentile speed. The speed limit may be rounded either up or down from the 85th percentile speed. The speed limit may also be rounded down an additional 5 mph if findings are made that the road has conditions which would not be apparent to a motorist unfamiliar with the road. The 85th percentile for the section from Green Canyon Road to Highway 76 was 56.2 mph, and the TAC made findings of limited shoulders and an injury collision rate higher than the statewide average to justify the 50 mph speed limit on that portion.

South Mission Road is a striped four-lane roadway with a raised planted median between 860 feet south of Pepper Tree Lane and Winter Haven Road, and is primarily a striped two-lane roadway, including three segments with a two-way left turn lane, between Winter Haven Road and Green Canyon Road. The TAC seeks to avoid short speed limit segments (other than school zones or other automatic speed limit zones), but the approximate one-mile length of each segment allowed for the possibility of different speed limits due to the different road characteristics.

Including the median South Mission Road between 860 feet south of Pepper Tree Lane and Winter Haven Road ranges in width from 70 feet to 90 feet while the width between Winter Haven Road and Green Canyon Road is 40 feet. Bicycle lanes are along both sides of the road, and South Mission Road is classified as a Major Road in the Mobility Element of the county's general plan. Fallbrook High School and Ivy High School are on the east side of the road between Stage Coach Lane and Winter Haven Road, which creates a 25 mph speed zone when children are present.

An April 2016 traffic survey at Green Canyon Road indicated a two-way average daily volume of 21,532 vehicles on South Mission Road. The Board of Supervisors placed that intersection on the county's Traffic Signal Priority List in January 2017 and volume warrants were based on an October 2014 traffic survey indicating an average daily volume of 21,960 vehicles approaching that three-way intersection consisting of 10,570 northbound and 10,230 southbound vehicles along South Mission Road and 1,160 westbound vehicles on Green Canyon Road. A January 2009 traffic survey of South Mission Road at Green Canyon Road produced an average daily volume of 19,300 vehicles.

During the 62-month period between Jan. 1, 2011, and Feb. 29, 2016, 80 vehicle collisions were reported on the 2.05-mile segment including 37 which involved injury and one with a fatality.

In 2010 a speed survey 1,900 feet north of Green Canyon Road indicated an 85th percentile speed of 60.0 mph with 57.4 percent of the drivers traveling within a 10 mph pace of 47-56 mph while a speed survey 1,630 feet south of Pepper Tree Lane resulted in an 85th percentile of 47.0 mph with 87.4 percent of the drivers within a pace of 40-49 mph. Because the speed limit south of Green Canyon Road is 50 mph in 2010 the TAC suggested a 50 mph speed limit for the entire segment to provide consistency rather than a 60 mph segment and two 50 mph segments.

The 2016 speed surveys utilized a Jan. 8 survey 300 feet north of Sterling Bridge and an April 21 survey 1,500 feet north of Green Canyon Road. The speed survey 300 feet north of Sterling Bridge was taken between 9:15 and 11:15 a.m. and produced an 85th percentile speed of 53.3 mph with 88.0 percent of the 229 drivers within a 45-54 mph pace. The speed survey 1,900 feet north of Green Canyon Road was conducted between 9:40 and 11:40 a.m. and the 177 vehicles had an 85th percentile speed of 55.5 mph with 82.0 percent within a 46-55 mph pace. The combined 406 drivers at the two locations crossed the survey point at an 85th percentile of 53.8 mph with 85.0 percent of the drivers within a 46-55 mph pace.

The TAC initially considered recertification of the segment from 860 feet south of Pepper Tree Lane to Green Canyon Road on March 10, 2017, but requested studies on separate segments before opting to make any recommendations. Although no new speed surveys were conducted, separate collision data was provided for the four-lane and two-lane segments and covered a 24-month period from July 1, 2015, to June 30, 2017.

A total of 29 collisions during those 24 months were reported on the four-lane portion of the roadway. The accident rate of 1.97 collisions per million vehicle miles exceeds the statewide average of 1.44 per million vehicle miles for similar divided four-lane roads with speed limits less than or equal to 55 mph. Ten of those collisions involved injury.

The two-lane segment had 15 reported collisions, including five in which injury occurred, during that period. The rate of 0.93 collisions per million vehicle miles compares favorably with the statewide average of 1.32 collisions per million vehicle miles for similar suburban two-lane roads with speed limits between 45 mph and 55 mph.

South Mission Road between Green Canyon Road and State Route 76 is classified as a Boulevard on the Mobility Element network. The striped two-lane through highway varies from 30 to 40 feet in width and has edge striping on both sides of the roadway. During the 24-month period from July 1, 2015, to June 30, 2017, the 46 reported accidents included 24 with injury. Although the accident rate of 1.01 collisions per million vehicle miles is lower than the statewide rate of 1.32 collisions per million vehicle miles for similar suburban two-lane roads with speed limits between 45 mph and 55 mph, the injury rate of 52.2 percent exceeds the statewide average of 41.1 percent.

Speed surveys were taken at Via Encinos Drive and 3,240 feet north of State Route 76. In 2010 the speed survey at Via Encinos Drive resulted in an 85th percentile speed of 53.8 mph with 75.2 percent of drivers within a 45-54 mph pace and the speed survey 3,240 feet north of State Route 76 indicated an 85th percentile of 56.8 mph with 69.8 percent of motorists within a 48-57 mph pace.

The 2017 speed survey at Via Encinos Drive was taken on May 23 between 9 and 11a.m. and measured 355 vehicles. The 85th percentile was 54.1 mph with 86.0 percent of drivers within a 46-55 mph pace. A May 25 speed survey 3,240 feet north of State Route 76 was conducted between 11 a.m. and 1 p.m., and the 436 vehicles had an 85th percentile of 57.3 mph while 74.0 percent of the drivers were within a 47-56 mph pace. The cumulative 791 vehicles had 79.0 percent of the drivers within a 46-55 mph pace as well as the 85th percentile of 56.2 mph.