Traffic  &  Congestion  on  Clay  Street 

Clay Street is the main road for drivers who live in the four contiguous neighborhoods situated in South Sonoma between Broadway and Fryer Creek. It is also the only street that commercial drivers use to get to the busy loading dock at the Lodge at Sonoma, which is located 160 feet from Broadway. In effect, the Lodge uses Clay as its private alley. For sixteen years, residents have had to contend with getting around trucks parked at the dock. Jackknifed trucks present unsafe obstacles in the middle of Clay, while more trucks line the curbs on both sides of Clay from Broadway to Bragg. Large tourist buses and limousines are frequently parked along Clay Street. Click on Clay Street tab above, in the Menu bar.


The loading dock at the Lodge does not meet any acceptable planning standards. The entire Clay Street width area is needed to allow for current truck loading/unloading activities. The proposed development would add 324 vehicle trips per day, according to estimates by the Institute of Traffic Engineers,

and would compound the problems that already exist. 


Dock Planning Standards


The curb should be redlined across from the dock, on Clay Street from Bragg to Broadway to 1) allow the truck maneuvering space needed to accommodate the loading dock and  2) prevent displaced commercial vehicles from idling their engines or parking next to the residences at Clay and Bragg. 


In the Spring, Summer, and Fall Clay Street is a favored parking destination for families going to Train Town. It is not uncommon for 50-100 vehicles, including large recreational vehicles, to be parked on Clay on weekends and holidays. 

Traffic and Safety

The developer proposes only 65 on site parking spaces for residents. This necessarily means there will be more competition for street parking in an area that is often over parked, resulting in much more traffic in the nearby family-friendly neighborhood as people drive around looking for parking. Frustrated drivers are often reckless drivers and residents in the surrounding neighborhoods don't think they should have to accommodate ever increasing traffic.


Community Environmental Defense Services


Main Road Traffic & Neighborhood Streets

As congestion increases on main routes, commuters tend to use less crowded neighborhood through streets as a way around congested road segments.  This action can greatly increase not only volume on the neighborhood street but average speed as well.  Because of this CEDS traffic engineers will assess development proposals for the likelihood of increasing traffic on local streets even if the project access is onto a main road.


Neighborhood Streets & Traffic Volume

In the portion of this webpage on Congestion, above, it was stated that unacceptable conditions may not occur until a single lane is carrying more 1,460 vehicles per hour.  Unfortunately, this same standard is the only one considered for neighborhood streets in far too many localities.  Instead, one should look at the volumes which trigger the need for Traffic Calming measures such as speed humps.  


Most traffic agencies use a threshold of 1,000- to 2,000-vehicles per day (vpd) before calming measures will be considered.  This volume of traffic would be generated by 83 to 200 homes along a street.  Proposed development projects should not cause traffic volume on an existing neighborhood street to exceed this volume.  If it will then the developer should be required to cover the cost of installing calming measures.  But even with calming measures traffic volume on a neighborhood street probably should not exceed 5,000 vpd.


Property Value Loss

The best way to prevent traffic from causing a property value loss is to keep traffic volume low and. most importantly, avoid the use of a neighborhood street by heavy trucks, like dump trucks as opposed to parcel delivery vans.



Noise Minimization

The best way to minimize noise on neighborhood streets is to keep traffic volume low.  It is particularly important to prevent land uses that generate large volumes of truck traffic from being sited at locations where these heavy, noisy vehicles must travel neighborhood streets. Highway noise can be disturbing for those living up to a mile from a high-speed, limited access road.  Noise barriers can reduce impacts for homes located within the noise shadow created by the barriers.  Forest and noise fences tend not to be very effective.



Trip Generation

The Institute of Transportation Engineers publishes the primary reference on this topic: Trip Generation.  This expensive tome contains trip generation rates for a large number of land uses.  The table below gives a few examples.   A more complete table can be found at: Common Trip Generation Rates.


Generally about 11% of the daily trips will occur during the evening rush hour and 10% during the morning rush hour.  Trip generation rates are usually given in vehicles per hour and refers to the rush-hour.


Air Quality & Health

A typical U.S. car emits enough pollution to create five tons of carbon dioxide a year. Cars and trucks produce half of all toxic air pollution emitted in the U.S. Estimates indicate that air pollution from cars results in 120,000 premature deaths each year in the U.S.  Traffic generated air pollution also accounts for $40-$50 billion in health care costs each year in this country.  In addition to these regional issues, some proposed development projects can create localized air quality problems.  Locating a truck stop next to homes could create a health issue if diesel engines are idling for long periods.  And whenever there is a large increase in truck traffic on a road lined with homes there will likely be an increase in the concentration of the particles emitted from diesel engines that account for most of the respiratory impact.  There is some evidence indicating that those living within 600 feet of a major highway may be particularly at risk due air pollution.  Large gas stations are another source but are addressed on the CEDS Convenience Stores & Gas Stations webpage.


Noise, Health & Property Value

Traffic noise can interfere with sleep, conversation, and other neighborhood pursuits. About 9.5% of us are exposed to traffic noise at a level which affects health.

Sound becomes noise when it interferes with our quality of life.  Sound is measured in units known as decibels (dB) and highway noise is measured on an “A-weighted decibel” (dBA) scale. 70 dBA is eight times as loud as 60 dBA. The noise level in a library might be 30 dBA while an air conditioner would emit 60 dBA.

Traffic volume, speed, and vehicle type all affect noise levels. At 2,000vehicles per hour (vph) traffic noise will sound twice as loud as at 200 vph. Traffic moving at 65 mph will sound twice as loud as at 30 mph. And one truck traveling at 55 mph will sound as loud as 28 cars moving at the same speed.


Traffic noise can have a significant effect on property value. A home located adjacent to a major highway may sell for 8% to 10% less when compared to one located along a quiet neighborhood street.  Heavy truck traffic lowers property value at a rate 150 times greater than cars. This is because at 50 feet heavy trucks emit noise at 90 dBA while a car traffic produces noise at a level of 50 dBA.5 An increase in heavy truck traffic may also cause damage to nearby homes through vibrations transmitted through the earth.

While some truck traffic is essential on neighborhood streets (e.g. refuse collection, delivery trucks, and fire engines) an increase in trucks passing through a neighborhood could lower property value and overall quality of life.  Land uses that generate large amounts of truck traffic, such as mining, landfills or power plants, should be sited where there's direct access to major highways; not residential streets.


Intersections with traffic signals and road segments are rated on a scale of A to F with regard to congestion.  This system is known as Level Of Service or LOS.  Most roads operate at a congestion-free "A" LOS during the wee hours of the morning.  But LOS is based upon conditions during the morning (7:00 - 9:00 am) and evening (4:00 - 6:00 pm) rush-hours.   An LOS of "E" and "F" is generally considered unacceptable.  In fact an "F" LOS is gridlock. 



Induced Traffic

A curious phenomenon, known as Induced Traffic, has been observed when a new road is opened in a congested area - traffic volume increases.  The explanation offered is that motorists who used to stay home to avoid congestion make more trips by car once a new road relieves congestion.  This is one of the many reasons why it is vitally important to carefully study every option for resolving congestion.  In fact, a number of officials have concluded that its usually not possible to resolve congestion just by building new roads.  This is particularly true when a new major road opens a rural area up for development.


David Goodison, Planning Director, Sonoma

Phone 707- 938-3681.



Planning Commissioners


Rachel Hundley, Mayor



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