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Thread: One-way street violations: what proportion of traffic constitutes a problem?

  1. #1
    Member
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    Iowa City, IA
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    One-way street violations: what proportion of traffic constitutes a problem?

    I am completing my exit project at university and am having a difficult time finding materials that identifies a threshold for vehicles violating traffic rules.

    At what point - what proportion - does a street's traffic amount to a "problem" that needs to be addressed? Where can I find such materials? Are these to be found through MPOs or are there national standards throughout the planing profession?

    Any suggestions would be greatly appreciated.

  2. #2
    maudit anglais
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    I'm not sure there is a hard and fast threshold for such a thing...though if engineers are involved they probably have tried to quantify it someone. I would suspect that the relationship is strongly weighted towards the risk of injuries/property damage.

  3. #3
    Cyburbian
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    Toronto, Canada
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    I am not aware of any formal definitions regarding the proportion of violations that is considered a problem, but I have a couple of thoughts that may help provide some context:
    1. Speed limits often set (or checked) using the 85%ile observed speed, which means that we expect 15% of drivers to exceed the limit. If the violation rate is much higher, it is more likely that the limit is set too low for the geometry and environment than a significant proportion of drivers are reckless. For instance, putting a primary school on a major arterial road and plunking down a 40 km/h school zone limit won't reduce speeds.
    2. Enforcement of traffic rules, apart from the persistent and sometimes valid rumors of speed traps being a revenue source, is usually not targeted until there have been complaints from community groups or elected representatives. This means there will likely be little enforcement of a 1-way rule in an area where the majority ignores it routinely (e.g. alleyways behind shops where delivery vehicles do whatever they have to in order to get the job done).
    It is an interesting question, but I don't think a set percentage of violations would ever work. Traffic rules are developed to improve either safety or operations efficiency (or both), and so if there are no significant problems with either of these goals in a given area (intersection, block, neighborhood), there is no reason to spent the money to enforce the rules, especially when enforcement would likely be seen as more of an irritation than violation.

    I'd be very interested to hear of any jurisdictions where they have established threshold violation rates to trigger enforcement activities.

  4. #4
    Cyburbian Random Traffic Guy's avatar
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    Jul 2005
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    Crashes (by numbers or spectacularness) or complaints (by numbers or prominence of complainer) which lead to news stories that embarrass elected officials seem to be the threshold around here.

  5. #5
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    What you are examining is getting into principals of traffic engineering although I am not sure what you mean by thresholds for "violating traffic rules." If you are looking for thresholds for say the number of cars that run red lights throughout the day, I don't think there are specific thresholds except for police incident data, or crash data.

    If you are interested in thresholds that measure the level of congestion at an intersection then probably what you need to research is the concept of Level of Service (LOS) which is defined by the Highway Capacity Manual (HCM). Your local DOT would have your state's acceptable LOS standards. Essentially LOS measures congestion at an intersection by delay time (usually in seconds), or through volume to capacity ratios (v/c ratio). In terms of delay, the higher the seconds of time that a vehicle waits at an intersection, the lower the LOS will be, and the intersection is determined to perform poorly. In terms of v/c ratio, the closer the v/c ratio is to 1.0, the worse the intersection performs and more likely that congestion will be worse. Try wikipediaing the term "Level of Service" and start from there. A lengthy explanation but hope the helps.

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