Here’s a question from a reader:
Since the widening of the 101 has been completed, I have waited for someone to finish painting the lanes in the following area: 101 south, Hwy 12 exit just after the on-ramp from Downtown/Railroad Square. Just before the exit splits to take either 12 west or east, there is a section of the offramp that is two lanes wide but is not distinguished as two lanes with paint. It is, however, declared two lanes by the signage above the off ramp that points to one lane being used to enter onto 101 south toward San Francisco and the other to take 12 to Sebastopol or Sonoma. Almost every time I enter this unpainted section of freeway, I have experienced a dangerous situation where drivers are on the right side of the very large lane but are exiting left and vice versa. This section seems like it has been overlooked for painting, and it needs to be remedied before an accident occurs. Jennifer of Santa Roa
The answer comes from Caltrans Transportation Engineer Thomas Kwok, who wrote:
Office of Traffic investigated the traffic concern … regarding the merging/diverging area from southbound US-101 to Highway 12, as follows:
We obtained an as-built pavement delineation plan (dated 4/21/2009) and compared that with our 1993 aerial photo record. Both of them show the exact same pavement delineation on the collector road.
From the plan, the merging/diverging area (which effectively is a wide lane) has a total length of 160m (or about 520 feet). If a lane line is added to delineate the collector road into two lanes as requested by … (the) reader, the area will effectively become a weaving area. The slightly curved lane configuration would reduce the effective weaving length to less than 450 feet. According to the design standards, Manual of Uniform Traffic Control Devices, the minimum weaving length should be 600 feet.
Under the current situation, a merging/diverging maneuver is considered operationally more forgiving to a motorist than a weaving movement. This is reflected in a negligible accident experience on the collector road.
Based on our record, there had been one reported collision in the latest three-year period from 4/1/2008 to 3/31/2011. It was a non-injury, rear-end collision.
Based on the above assessment, Office of Traffic does not recommend any changes to the pavement delineation that would alter the existing traffic movements.
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