Volume 2: Draft Gorst Planned Action Environmental Impact Statement

GORST PLANNED ACTION EIS | AFFECTED ENVIRONMENT, SIGNIFICANT IMPACTS, AND MITIGATION MEASURESRoadway LOSLOS designations are qualitative measures of congestion that describe operational conditions within a trafficstream and take into consideration such factors as volume, speed, travel time, and delay. LOS is represented byletter grades A through F. LOS A through C imply traffic flows with minimal delay, while LOS D and E implyconditions that approach capacity, and LOS F implies unstable flow with potential for substantial delays(Transportation Research Board 2000). The characteristics of the six LOS designations for roadway segments andintersections are summarized in Table 3.11-2 LOS Descriptions. The LOS scale has been adopted by the Institute ofTransportation Engineers, the Transportation Research Board, and by most jurisdictions throughout the country.Methods applied to calculate LOS for roadway segments and intersections is described later in this chapter inMethodology.ABCDETable 3.11-2LOS DescriptionsLOS Roadways IntersectionsDescribes primarily free-flow operations ataverage travel speeds, usually about 90percent of the free-flow speed for the arterialclass. Vehicles are completely unimpeded intheir ability to maneuver within the trafficstream. Stopped delay at signalizedintersections is minimal.Represents reasonably unimpeded operationsat average travel speeds, usually about 70percent of the free-flow speed for the arterialclass. The ability to maneuver within the trafficstream is only slightly restricted and stoppeddelays are not bothersome. Drivers are notgenerally subjected to appreciable tension.Represents stable conditions; however, abilityto maneuver and change lanes in mid-blocklocation may be more restricted than at LOS B,and longer queues and/or adverse signalcoordination may contribute to lower averagetravel speeds of about 50 percent of theaverage free-flow speed for the arterial class.Motorists will experience appreciable tensionwhile driving.Borders on a range in which small increases inflow may cause substantial increases inapproach delay and, hence, decreases inarterial speed. This may be due to adversesignal progression, inappropriate signal timing,high volumes, or some combination of these.Average travel speeds are about 40 percent offree-flow speed.Characterized by significant approach delaysand average travel speeds of one-third thefree-flow speed or lower. Such operations arecaused by some combination of adverseprogression, high signal density, extensivequeuing at critical intersections, andinappropriate signal timing.Describes operations with low control delay, up to 10seconds per vehicle (s/veh). This LOS occurs whenprogression is extremely favorable and most vehiclesarrive during the green phase. Many vehicles do notstop at all. Short cycle lengths may tend to contributeto low delay values.Describes operations with control delay greater than10 and up to 20 s/veh. This level generally occurs withgood progression, short cycle lengths, or both. Morevehicles stop than at LOS A, causing higher levels ofdelay.Describes operations with control delay greater than20 and up to 35 s/veh. These higher delays may resultfrom only fair progression, longer cycle lengths, orboth. Individual cycle failures may begin to appear atthis level. Cycle failure occurs when a given greenphase does not serve queued vehicles, and overflowsoccur. The number of vehicles stopping is significant atthis level, though many still pass through theintersection without stopping.Describes operations with control delay greater than35 and up to 55 s/veh. At LOS D, the influence ofcongestion becomes more noticeable. Longer delaysmay result from some combination of unfavorableprogression, long cycle lengths, and high vehicle-tocapacity(V/C) ratios. Many vehicles stop, and theproportion of vehicles not stopping declines. Individualcycle failures are noticeableDescribes operations with control delay greater than55 and up to 80 s/veh. These high delay valuesgenerally indicate poor progression, long cycle lengths,and high V/C ratios. Individual cycle failures arefrequent.Draft | June 2013 3-155