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.The social-outcome rating is based on a combination of theindividual-safety, economic-efficiency, environment, and equity ratings.The implementation-obstacle rating, in turn, is based on a combinationof the individual-stakeholder-concern, general-political-obstacle, andinstitutional-obstacle ratings.The final set of ratings used to compareand contrast strategies is as follows:net cost/revenue implicationsshort-term effectiveness in reducing congestionlong-term effectiveness in reducing congestionmobility, accessibility, and traveler-choice outcomessocial outcomes (composite rating)implementation obstacles (composite rating)current status in the L.A.region.The Social-Outcome Composite RatingThe social-outcome rating, which provides an average of the individual-safety, economic-efficiency, environment, and equity ratings, is con-structed as follows.First, the score on each individual rating isconverted to a numeric value (see Table A.3).The scores of the fourindividual strategies are then added together, and the resulting sum istranslated into a composite rating (see Table A.4).Table A.3Social-Outcome Rating: ConvertingIndividual Ratings to Numeric ValuesRating Numeric ScoreVery bad 2Bad 1Neutral 0Good 1Very good 2 Strategy-Rating Overview 195Table A.4Social-Outcome Rating: Composite ScoresSum of Individual Ratings Composite Rating 8 to 6 Very bad 5 to 2 Bad 1 to 1 Neutral2 to 5 Good6 to 8 Very goodThe Implementation-Obstacle Composite RatingThe implementation-obstacle rating, which combines the individual-stakeholder-concern, general-political-obstacle, and institutional-obstacle ratings, is constructed as follows.First, the score on each indi-vidual rating is converted to a numeric value (see Table A.5).The scoresof the three individual strategies are then added together, and theresulting sum is translated into a composite rating (see Table A.6).Note that these scores are deliberately weighted toward the higherend.The logic is that even a single obstacle can make implementationdifficult.Multiple obstacles will further compound this difficulty.Table A.5Implementation-Obstacle Rating:Converting Individual Ratings to NumericValuesRating Numeric ScoreLow 1Medium 2High 3 196 Moving Los Angeles: Short-Term Policy Options for Improving TransportationTable A.6Implementation-Obstacle Rating:Composite ScoresSum of Individual Ratings Composite Rating3Low4 Medium-low5 Medium6 Medium-high7 to 9 High APPENDIX B1Freeway-Ramp MeteringRamp metering involves the use of traffic lights at freeway-entranceramps, where signals are timed to even out the stream of vehicles merg-ing into the main lanes.The intent is to reduce bottlenecks and disrup-tions that might occur if a large number of vehicles entered the freewayat the same time, which should, in turn, help maintain a smootherflow of traffic in the freeway lanes.Ramp meters may also discouragemotorists from using the freeway for short distances, diverting theminstead to arterial streets.There are at least three generations of ramp-metering technology (Caltrans District 7, 2007):Fixed-time and time-of-day meters: These are the simplest formof ramp meters.Metering periods and cycle lengths are presetbased on historical data.These meters are not responsive to cur-rent freeway-flow conditions, but they will respond to long queuesthat fill up ramp storage and spill into adjacent arterial streets.When this occurs, a sensor in the ramp will trigger a signal torelease cars from the ramp onto the freeway until the backup isrelieved.Traffic-responsive meters: These systems have the same features asfixed-time meters but are also capable of adjusting metering ratesbased on current traffic conditions on the freeway itself.Control-lers are able to override fixed timing plans when appropriate (thatis, when current freeway conditions can accommodate more carsentering in close sequence).These systems detect conditions onthe freeway only immediately upstream from the on-ramp and donot consider wider conditions throughout the freeway network.197 198 Moving Los Angeles: Short-Term Policy Options for Improving TransportationSWARM: These meters optimize traffic flow onto freeways by con-sidering actual and predicted conditions throughout the freewaysystem.SWARM technology is also responsive to recurrent andnonrecurrent congestion.However, it requires a computerizedcommunication center to calculate real-time adjustments alongwith a communication system to relay traffic detection from thefield and metering plans back out to ramp meters.Ramp metering was introduced in 1963 on the EisenhowerExpressway in Chicago.Los Angeles soon followed suit, deploying itsfirst ramp-metering technology in 1969 (Caltrans District 7, 2007).By 1995, freeway-ramp metering had been implemented or was inthe final design stages in 23 metropolitan areas in North America,including Atlanta, Dallas, Denver, Detroit, Fresno, Miami, Milwau-kee, Montreal, New York, Ottawa, Phoenix, Riverside, Sacramento,San Diego, and Seattle (Piotrowicz and Robinson, 1995) [ Pobierz całość w formacie PDF ]
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.The social-outcome rating is based on a combination of theindividual-safety, economic-efficiency, environment, and equity ratings.The implementation-obstacle rating, in turn, is based on a combinationof the individual-stakeholder-concern, general-political-obstacle, andinstitutional-obstacle ratings.The final set of ratings used to compareand contrast strategies is as follows:net cost/revenue implicationsshort-term effectiveness in reducing congestionlong-term effectiveness in reducing congestionmobility, accessibility, and traveler-choice outcomessocial outcomes (composite rating)implementation obstacles (composite rating)current status in the L.A.region.The Social-Outcome Composite RatingThe social-outcome rating, which provides an average of the individual-safety, economic-efficiency, environment, and equity ratings, is con-structed as follows.First, the score on each individual rating isconverted to a numeric value (see Table A.3).The scores of the fourindividual strategies are then added together, and the resulting sum istranslated into a composite rating (see Table A.4).Table A.3Social-Outcome Rating: ConvertingIndividual Ratings to Numeric ValuesRating Numeric ScoreVery bad 2Bad 1Neutral 0Good 1Very good 2 Strategy-Rating Overview 195Table A.4Social-Outcome Rating: Composite ScoresSum of Individual Ratings Composite Rating 8 to 6 Very bad 5 to 2 Bad 1 to 1 Neutral2 to 5 Good6 to 8 Very goodThe Implementation-Obstacle Composite RatingThe implementation-obstacle rating, which combines the individual-stakeholder-concern, general-political-obstacle, and institutional-obstacle ratings, is constructed as follows.First, the score on each indi-vidual rating is converted to a numeric value (see Table A.5).The scoresof the three individual strategies are then added together, and theresulting sum is translated into a composite rating (see Table A.6).Note that these scores are deliberately weighted toward the higherend.The logic is that even a single obstacle can make implementationdifficult.Multiple obstacles will further compound this difficulty.Table A.5Implementation-Obstacle Rating:Converting Individual Ratings to NumericValuesRating Numeric ScoreLow 1Medium 2High 3 196 Moving Los Angeles: Short-Term Policy Options for Improving TransportationTable A.6Implementation-Obstacle Rating:Composite ScoresSum of Individual Ratings Composite Rating3Low4 Medium-low5 Medium6 Medium-high7 to 9 High APPENDIX B1Freeway-Ramp MeteringRamp metering involves the use of traffic lights at freeway-entranceramps, where signals are timed to even out the stream of vehicles merg-ing into the main lanes.The intent is to reduce bottlenecks and disrup-tions that might occur if a large number of vehicles entered the freewayat the same time, which should, in turn, help maintain a smootherflow of traffic in the freeway lanes.Ramp meters may also discouragemotorists from using the freeway for short distances, diverting theminstead to arterial streets.There are at least three generations of ramp-metering technology (Caltrans District 7, 2007):Fixed-time and time-of-day meters: These are the simplest formof ramp meters.Metering periods and cycle lengths are presetbased on historical data.These meters are not responsive to cur-rent freeway-flow conditions, but they will respond to long queuesthat fill up ramp storage and spill into adjacent arterial streets.When this occurs, a sensor in the ramp will trigger a signal torelease cars from the ramp onto the freeway until the backup isrelieved.Traffic-responsive meters: These systems have the same features asfixed-time meters but are also capable of adjusting metering ratesbased on current traffic conditions on the freeway itself.Control-lers are able to override fixed timing plans when appropriate (thatis, when current freeway conditions can accommodate more carsentering in close sequence).These systems detect conditions onthe freeway only immediately upstream from the on-ramp and donot consider wider conditions throughout the freeway network.197 198 Moving Los Angeles: Short-Term Policy Options for Improving TransportationSWARM: These meters optimize traffic flow onto freeways by con-sidering actual and predicted conditions throughout the freewaysystem.SWARM technology is also responsive to recurrent andnonrecurrent congestion.However, it requires a computerizedcommunication center to calculate real-time adjustments alongwith a communication system to relay traffic detection from thefield and metering plans back out to ramp meters.Ramp metering was introduced in 1963 on the EisenhowerExpressway in Chicago.Los Angeles soon followed suit, deploying itsfirst ramp-metering technology in 1969 (Caltrans District 7, 2007).By 1995, freeway-ramp metering had been implemented or was inthe final design stages in 23 metropolitan areas in North America,including Atlanta, Dallas, Denver, Detroit, Fresno, Miami, Milwau-kee, Montreal, New York, Ottawa, Phoenix, Riverside, Sacramento,San Diego, and Seattle (Piotrowicz and Robinson, 1995) [ Pobierz całość w formacie PDF ]