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i Acknowledgements  v List of Tables  ix List of Figures  xi 1.0 Introduction  1 1.1 Variable Speed Limits 2 1.2 OR 217 VSL System Background  6 1.3 Motivation & Objectives 8 1.4 Organization  9 2.0 Literature Review 10 2.1 History 10 2.2 System Types & Purposes  13 2.2.1 Weather-Responsive  13 2.2.2 Congestion-Responsive 14 2.2.3 Work Zone Systems  15 2.3 Evaluation Methods & Performance Measures  15 2.3.1 Before and After Evaluation Methods  17 2.4 Evaluation Results  19 2.4.1 Effects on Congestion & Operations  19 2.4.2 Effects on Safety and Adverse Weather Performance  21 2.4.3 Simulation Results  22 2.5 Summary  23 3.0 Motivations for VSL on OR 217  25 3.1 Corridor Almanac  25 3.2 Crash Trends  27 3.3 Effects of Adverse Weather  29 3.4 Speeds, Flows, & Travel Times  31 3.5 Bottleneck Patterns  37 3.6 Summary  39 vii 4.0 Methodology  41 4.1 Corridor Instrumentation  41 4.2 Data Description  48 4.2.1 Traffic Flow Data  48 4.2.2 Crash & Incident Data  49 4.2.3 Weather Data  51 4.3 Evaluation Framework  51 4.4 Analysis Techniques  54 4.4.1 Speed Variation  54 4.4.2 Crash & Incident Frequency and Distribution  57 4.4.3 Adjacent Lane Flow & Speed Distribution  60 4.4.4 Travel Time Reliability  62 4.4.5 Bottleneck Flow Characteristics  66 4.4.6 Impact of Adverse Weather on Performance  70 4.5 Summary  72 5.0 Results & Discussion  73 5.1 Wavetronix Analysis  73 5.1.1 Traffic Speeds and Volumes  73 5.1.2 Travel Time Comparison  77 5.2 Speed Variation  83 5.2.1 Allen Boulevard and Denney Road Speed Variation  83 5.2.2 Scholls Ferry and Greenburg Speed Variation  88 5.2.3 Discussion  91 5.3 Crash & Incident Frequency and Distribution  94 5.3.1 Incident Trees 95 5.3.2 Crash Frequency  99 5.3.3 Crash Distribution  100 5.3.4 Discussion  105 5.4 Adjacent Lane Flow & Speed Distribution  106 5.4.1 Greenburg Road Lane Flow & Speed Distribution 107 5.4.2 Lane Flow & Speed Distribution at Other Stations  111 viii 5.4.3 Discussion  116 5.5 Travel Time Reliability  119 5.5.1 OR 217 NB Travel Times  119 5.5.2 OR 217 SB Travel Times  126 5.5.3 OR 217 Volume Comparison 132 5.5.4 Discussion  138 5.6 Bottleneck Flow Characteristics  143 5.6.1 Northbound Bottlenecks  144 5.6.2 Southbound Bottlenecks  152 5.6.3 Discussion  156 5.7 Impact of Adverse Weather on Travel Time  159 5.7.1 Effect of Precipitation on Travel Times 159 5.7.2 Effect of Precipitation on Travel Time Variability  164 5.7.3 Discussion  167 5.8 Summary  171 6.0 Conclusions  178 6.1 Contributions 181 6.2 Limitations  182 6.3 Future Research  184 References  189

Evaluating the Effects of a Congestion and Weather Responsive Advisory Variable Speed Limit System in Portland, Oregon