managing travel for planned special events - FHWA Operations ...

congestion is considered either recurringor non-recurring based on its causal factors:• Recurring congestion is usually characterizedby an increase in traffic demand.Commuter traffic induces congestion atthe same time and location weekday afterweekday; hence traffic managers canessentially predict when recurring congestionwill happen. Recurring congestionreflects the daily, systematic relationshipbetween peak traffic demandrates, inadequate road capacity, and suboptimaloperation of traffic control devices.The latter represents one of thefew causes of recurring congestion thataffects capacity rather than demand.• Non-recurring congestion happens as aresult of an event. The spatial and temporalcharacteristics, or location andtime of an event, may be known in advance,or the event may happen at randomwith very little or no warning.These events are commonly termedplanned and unplanned events, respectively.Congestion causing events,whether planned or unplanned, result ineither a reduction in roadway capacity,an increase in traffic demand, or both.Table 1-1 summarizes how these eventsimpact roadway system operations.A planned special event represents the onlytype of event that can generate an increase intraffic demand and cause a temporary reductionin roadway capacity because of eventstaging. For example, a parade or bicyclerace may require street closures extendingover a significant distance, and other eventsmay warrant isolated road closures to accommodatepedestrian flow.Planned EventTable 1-1Congestion Impacts of Planned and Unplanned EventsEVENT-GENERATED IMPACTEVENT CATEGORYMajor roadway constructionand maintenanceTRAFFIC DEMAND• Increases background trafficdemand on parallel freewaysand arterials.Planned special event • Generates new trips and increasestraffic demand on allcorridors serving the event.ROAD CAPACITY• Closes travel lane(s) or roadsegments.• Closes travel lane(s) or roadsegments to stage event (typicallystreet use events).Unplanned EventTraffic incident(e.g., crash, disablement,spilled load, debris)• Causes background traffic diversionto parallel freeways andstreets.Emergency road work • Causes background traffic diversionto parallel freeways andstreets.Adverse weather(e.g., snow, ice, fog, heavyrain, sun glare)Emergency(e.g., severe weather, naturaldisaster, terrorism)• Decreases traffic demand (potentially).• Causes evacuations that generateextreme traffic demand.• Blocks travel lane(s) or roadsegments.• Blocks travel lane(s) or roadsegments.• Reduces vehicle operatingspeeds and increases headways,thus reducing capacity.• Renders road segments impassable(potentially).1-2