February 4, 2009 > The need for speed... limits
The need for speed... limits
Often ignored or given scant notice, ubiquitous speed limit signs planted along roads are nonetheless important indicators of law enforcement expectations of drivers as they travel through cities. Continued inattention often leads to the sight in a rear view mirror of flashing red lights and an expensive pause before completing a journey. Whether cursed as impractical or commended for safety considerations, for many, the origin of speed limits is a mystery.
During the waning months of 2008, the Fremont City Council received an explanation of city speed limits and suggested modifications from Senior Transportation Engineer David Huynh. TCV asked Mr. Huynh to answer questions for our readers as well.
TCV: How often are speed limits reviewed?
Huynh: As a public agency, we are regulated by the California Vehicle Code. Depending on conditions, speed limits are reviewed, at a maximum, every five, seven or ten years. Our general practice has been to do it every seven years. The five year requirement must be met if your police department is not certified in use of a radar gun. The seven year requirement is followed if radar gun use is certified. If the traffic engineer certifies that at the seven year mark nothing has changed and there is no need for modification, the time is extended to ten years.
TCV: What can cause a change or review of speed limits before a seven year review?
Huynh: The timeline may be altered if there is a significant change in the roadway or a new roadway is created such as at Pacific Commons. Typically, engineers have designed a road for a certain speed. That may be the original speed but then a survey is conducted to measure actual driving speeds which can confirm or modify the posted limit.
TCV: Does the accident rate on a particular roadway trigger a review?
Huynh: No. A review can be done, but is not mandated by accidents.
TCV: Are there any regulations that required adjacent roadways to be within a certain speed limit of each other?
Huynh: If the characteristics of the street change drastically, it could happen. For instance if a residential street with a speed limit of 25 miles per hour feeds a high speed street, the speed limit could change drastically. However, in most cases this does not happen and common sense would dictate a more gradual change.
TCV: How does a review change current speed limits?
Huynh: This is determined by drivers. Our data collection measures the speed of drivers on a particular roadway. Speed limits are actually a very democratic process; drivers vote with their cars. We can, however, modify our recommendation to a speed that may be below survey results due to a variety of factors such as accident rates, high incidence of pedestrian or bicycle activity and things of that nature. Residential areas, however, are set at a default of 25 miles per hour but could be justified at a different speed. State roads, such as portions of Mission Boulevard, are not under our jurisdiction.
TCV: How and when is the data collection done?
Huynh: Guidelines dictate that we measure 'free flow' during times of the day that allow such movement. Usually rush hours are traveled at slower speeds due to congestion, so those times are not monitored. This measurement is supposed to give an accurate reading of speeds at which drivers feel safe, confident and unimpeded. Inconspicuous measurements are taken by radar using the same device used by police to enforce the limits. This is done on all streets not under de facto limits such as the 25 mile per hour limit used for residential streets.
There are two documents that regulate how we set speed limits: California Vehicle Code and California Manual on Uniform Traffic Control Devices. These determine how we can determine speed limits and how they are posted. The limit is typically effective at the point of posting which is usually at the far side of an intersection. We make a recommendation to the city council based on our survey and their decision modifies a city ordinance.
TCV: Are speed limit recommendations made with input from the police department?
Huynh: Yes. We ask for feedback on factors such as accidents statistics and records and try to reach a consensus.