The San Diego County Board of Supervisors reduced the speed limit on Potrero Valley Road between State Route 94 and Potrero Park Road.
A 5-0 vote Oct. 16 approved the introduction and first reading of the ordinance amendment to reduce the speed limit for the 0.69-mile segment from 40 mph to 35 mph while retaining certification for radar enforcement and a 5-0 vote October 30 approved the second reading and adoption. The new speed limit will be effective November 29, although the county’s Department of Public Works (DPW) may post new signs earlier than that.
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. Periodic recertification, including a supporting speed survey, is required for continued radar enforcement and DPW or a contractor typically conducts speed surveys every seven years. 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.
Potrero Valley Road is a two-lane roadway with a travel width of 24 feet and a road bed width of 28 feet. The roadway is striped with a white edge line and double yellow center lines which prohibit passing. The mobility element of the county’s general plan classifies Potrero Valley Road as a minor collector.
A November 2012 traffic survey taken north of State Route 94 indicated a two-way average daily volume of 1,060 vehicles. The May 22, 2019, traffic survey at that location counted 1,774 vehicles consisting of 920 northbound and 854 southbound motorists. The heaviest hourly volumes were 190 vehicles between 3:00 p.m. and 4:00 p.m., 125 motorists between 2:00 p.m. and 3:00 p.m., and 124 drivers between 9:00 a.m. and 10:00 a.m.
The only reported collision between February 1, 2016, and January 31, 2019, did not involve an injury and gave the segment a collision rate of 0.75 per million vehicle miles. The statewide average for similar rural flat conventional two-lane roads with speed limits less than or equal to 55 mph is 0.99 per million vehicle miles.
In 2012 the speed survey taken 600 feet north of Library Lane indicated an 85th percentile of 43.1 mph with 64.5 percent of the drivers within a 10 mph pace of 29-38 mph. The speed survey taken at that location on May 8, 2019, produced an 85th percentile of 37.9 mph with 63.0 percent of drivers in a 27-36 mph pace. The most frequent speeds in the speed survey were 32 mph and 35 mph with 12 vehicles apiece and 25 mph with ten drivers.
The county’s Traffic Advisory Committee recommended reducing the speed limit during the July 26 TAC meeting.