Urban Street Safety, Operation, and Reliability

Transcription

1 Urban Street Safety, Operation, and Reliability March 2012 Overview Background Urban Street Operation Urban Street Safety Combined Operation and Safety Evaluation Reliability Evaluation 2 1

2 Background Observations Newly released Highway Safety Manual (HSM) provides a means to quantify road safety Reliability of service (e.g., travel time) is an important descriptor of operational performance Reliability is influenced by events (e.g., weather, crashes) that occur over the year Decisions to improve operation influence safety and vice versa Presentation Basis SHRP 2 Project L08: Incorporation of Travel Time Reliability into the Highway Capacity Manual (HCM) Scope Prediction (as opposed to measurement) to inform system design, operation, and management Urban Street Operation Operational Evaluation Analysis period Design hour Associated with a high volume Assume: if proposed facility adequately serves design hour, then it will provide adequate service during most other hours in year Peak hour factor represents a refinement to concept Evaluation of multiple hours often undertaken Operation influenced by design and control choices Intersection control mode: signal vs. stop control Left-turn mode: permitted, protected-permitted, protected-only Change interval duration Median type: raised curb, TWLTL, no median (undivided) Turn bay presence 2

3 Urban Street Operation Operational Evaluation HCM Approach 2010 Highway Capacity Manual Urban street facilities Urban street segments Signalized intersections Two-way stop-controlled intersections All-way stop-controlled intersections Roundabouts Interchange ramp terminals Urban street segments performance measures Travel time Travel speed Stop rate Through delay Urban Street Safety Safety Evaluation Analysis period One year Evaluation of all years during design life often undertaken Safety influenced by design and control choices Intersection control mode: signal vs. stop control Left-turn mode: permitted, protected-permitted, protected-only Change interval duration Median type: raised curb, TWLTL, no median (undivided) Turn bay presence 3

4 Urban Street Safety Safety Evaluation Traditional Approach Standards-based safety (nominal safety) Premise: adherence to controls and warrants ensures safety Guidance documents AASHTO Policy on Geometric Design of Highways and Streets AASHTO Roadside Design Guide Manual on Uniform Traffic Control Devices Individual state DOT manuals Urban Street Safety Safety Evaluation HSM Approach Quantified safety (substantive safety) 2010 Highway Safety Manual Urban street facilities Urban street segments Signalized intersections Two-way stop-controlled intersections All-way Stop-Controlled Intersections Roundabouts Interchange ramp terminals (forthcoming) Urban street performance measures Expected crash frequency Fatal and injury, single vehicle Fatal and injury, multiple vehicle Property damage only, single vehicle Property damage only, multiple vehicle 4

5 Combined Operation and Safety Evaluation Consideration of Operations and Safety Effect of design and control choices can be quantified Effect on operational performance Effect on safety performance HSM makes combined, quantitative assessment possible Combined Operation and Safety Evaluation Issue 1 Time Domain of Evaluation Operations: design hour Safety: one year How well can the design hour reflect year-round performance? Safety Evaluation Hour 24 Traditional Operational Evaluation Use HCM to estimate travel time for design hour. Hour 24 Use HSM to estimate expected crash frequency for year Day of Year Day of Year 5

6 Combined Operation and Safety Evaluation Issue 2 Operations and Safety Not Independent Design and control choices to improve operation influence safety and vice versa Improvements in operation do not necessarily improve safety and vice versa Combined Operation and Safety Evaluation Whole-Year Analysis A way to resolve these issues Temporally disaggregated system analysis Evaluate operations for every hour of the year Or, perhaps just selected hours of each day (e.g., pm peak period) Computation time Fast computing speeds available with today s computer A software tool implementing the HCM (or any deterministic macroscopic) model can be executed in a fraction of a second Features Adjust traffic volumes for hour of day, day of week, and month of year variation Include consideration of external events Weather Non-crash incidents (e.g., breakdown, debris in road, etc.) Infrastructure failure (e.g., signal malfunction, dangerous potholes) Train presence 6

7 Combined Operation and Safety Evaluation Whole-Year Analysis Evaluate every hour of interest during the year Combined Operation and Safety Evaluation Whole-Year Analysis Feasible with 2010 HCM and 2010 HSM Temporal disaggregation not supported in 2010 HSM Whole-Year Operational Evaluation Safety Evaluation Hour 24 Use HCM to estimate travel time for every hour of year.* Hour 24 Use HSM to estimate expected crash frequency for year Day of Year Day of Year 7

8 Combined Operation and Safety Evaluation Whole-Year Analysis Perhaps next edition of HSM will support temporal disaggregation of safety prediction SHRP 2 Project L08 research has developed a procedure Whole-Year Operational Evaluation Whole-Year Safety Evaluation Hour 24 Use HCM to estimate travel time for every hour of year.* Hour 24 Use HSM to estimate expected crash frequency for year Day of Year Day of Year Combined Operation and Safety Evaluation Issue 3 Work Zones and Special Events Design and control decisions made to accommodate work zones When, and how long, to accommodate work zone also a factor All can be evaluated using whole-year analysis 8

9 Combined Operation and Safety Evaluation Payoff of Whole-Year Analysis More complete picture of overall facility performance Distribution of performance during year Both safety and operations Travel Time Weather Incident Lane Hours Blocked Incidents per Day Severe crash, many lanes Combined Operation and Safety Evaluation Payoff of Whole-Year Analysis Implement strategies to reduce incidents or mitigate their impact Example: add shoulder (disabled vehicle refuge) No change in operation during design hour, but Average travel time decreases and operation is more reliable Travel Time Lane Hours Blocked 9

10 Combined Operation and Safety Evaluation Payoff of Whole-Year Analysis Implement strategies to increase speed and reduce delay Example: convert from protected-only to protected-permitted lefts Travel time decreases during design hour (+ other hours), but Crashes increase, Average travel time is unchanged, and operation is less reliable Travel Time Incidents per Day Disclaimer: Trends are illustrative. One design or control change may not produce such dramatic distribution shifts but a combination of changes could produce such shifts. Combined Operation and Safety Evaluation Reliability Evaluation A variation of whole-year analysis Emphasis on operations 10

11 Reliability Evaluation Project L08 Overview Framework Overview of next three parts Scenario Generation Facility Evaluation Performance Summary Illustrative Analysis Capabilities 21 Project L08 Overview SHRP 2 Project L08 Incorporation of Travel Time Reliability into the Highway Capacity Manual Objectives Determine how non-recurrent congestion impacts can be incorporated into HCM procedures Develop methodologies to predict travel time reliability on freeway facilities and urban streets Address freeway and urban streets in a corridor context Prepare a guide with that is suitable for potential inclusion in a future update of the HCM 2010 Project schedule Ends October

12 Framework Development Goals for Urban Streets Incorporate HCM Urban Streets methodology Quantify the effect of non-recurring congestion sources Weather Demand variation Incidents Work zones Special events Minimize the amount of required input data Assemble a set of nationally-representative default values Terms Scenario a unique combination of volume and traffic control conditions for one analysis period (e.g., 1 hour) Study period one or more consecutive scenarios during a day (e.g., 3-hour period from 3:30 pm to 6:30 pm) 23 Framework Manual Software Work Flow Start with the input data used to evaluate an urban street facility using the 2010 HCM Urban Streets methodology Enter the data in the urban streets engine and save it to a file If desired, enter and save data for each work zone or special event Read the file and use it as a basis for scenario generation Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year... Predict weather events Predict incident events Adjust speed and saturation flow rate based on events Adjust demand volumes using hourly, weekly, monthly factors Save one revised file for each analysis period Submit each revised file to the urban streets engine Collect performance measures and compute reliability statistics 24 12

13 Framework Flow Chart 25 Framework Input Data Nearest city Functional class Analysis period duration (0.25 hr or 1.0 hr) Study period duration (e.g., 7:00 am, extend for 3 hours) Reliability reporting period (e.g., 1/1/2011, extend for 365 days) Days of week considered (Su, M, Tu, W, Th, F, Sa) Crash frequency by Segment Intersection If work zone or special event present Operating period (e.g., 4/1/2011, extend for 30 days) Crash frequency adjustment factors 13

14 Framework Work Zones and Special Events Each is dealt with as a unique case for a unique time period Identify volume, geometry, and signal timing for each case Include specific changes due to work zone or special event» Lane closures» Alternative lane assignments» Special signal timing Create one urban streets engine input file for each case Establish operating period (e.g., 4/1/2011, extend for 30 days) Determine crash frequency adjustment factors Traffic demand changes Not predicted If analyst can estimate demand shifts, they can be reflected in volumes entered in the input file Urban Streets Reliability Engine Welcome 28 14

15 Step 1. Scenario Generation Set Up 29 Step 1. Scenario Generation Set Up 30 15

16 Step 1. Scenario Generation 31 Urban Streets Reliability Methodology Framework Overview of next three parts Scenario Generation Facility Evaluation Performance Summary Illustrative Analysis Capabilities 32 16

17 Scenario Generation Considerations Weather Event Procedure Traffic Demand Variation Procedure Traffic Incident Procedure Scenario File Generation Procedure Scenario Generation Considerations Stochastic and deterministic processes contribute to reliability Systematic variation addressed deterministically Stochastic processes addressed using Monte Carlo methods Weather Occurrence, rate, duration, and start time Demand 15-min flow rate Incident Occurrence, type, location, duration, and start time Variance control Fixed random number seed for each process Analyst controls seed value Keep seed at same value to compare alternatives, or Vary seed among replications to explore stochastic influence 17

18 Scenario Generation Weather Weather Event Procedure Analyst selects nearest city from list of 284 cities Data from National Climatic Data Center Mean number of days with precipitation Total snowfall Normal daily mean temperature Normal precipitation Average rainfall intensity Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year to predict... Clear, dry pavement Rainfall, wet pavement (including intensity) Clear, wet pavement Snowfall, snow on pavement (including intensity) Clear, snow on pavement Monte Carlo methods used to predict daily and hourly events 35 Scenario Generation - Demand Traffic Demand Variation Procedure Analyst selects functional class from list of three classes Data from 19 states assembled by Hallenbeck et al. Hour-of-day hourly volume variation Day-of-week AADT variation Month-of-year AADT variation Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year to predict... Volume adjustment factors for each hour 36 18

19 Scenario Generation - Incident Traffic Incident Procedure Analyst inputs crash frequency for segments and intersections Based on historic crash data or HSM predictive method Data from research literature and existing databases Incident frequency based on weather condition and crash frequency Distribution of incident type Segment, intersection Crash, non-crash Shoulder, one-lane closed, two or more lanes closed Fatal-or-injury, pdo, breakdown, other Incident duration Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year to predict... Incident type for specific intersection leg or segment travel direction Monte Carlo methods used to predict incident occurrence on hourly basis based on volume and incident frequency 37 Scenario Generation File Creation Scenario File Generation Procedure Analyst clicks Start Calculations button in Set Up worksheet Work day-by-day, analysis-period-by-analysis-period in chronologic order through the year to predict... Volume Use factors once to convert volume in input file to AADT Use factors a second time to compute volume for specific period based on AADT Monte Carlo methods used to add random volume variation to analysis periods in common hour If incident present at specific location Adjusted saturation flow rate Additional travel time Reduce number of lanes on segment If weather present Adjusted saturation flow rate Adjusted free-flow speed Create a new input file that has updated speed and sat. flow rates 19

20 Urban Streets Reliability Methodology Framework Overview of next three parts Scenario Generation Facility Evaluation Performance Summary Illustrative Analysis Capabilities 39 Facility Evaluation Procedure Work day-by-day, analysis-period-by-analysis-period in chronologic order Submit revised file to the engine Save evaluation results to output file Check residual queues Modify next input file if needed 20

21 Step 2. Facility Evaluation 41 Urban Streets Reliability Methodology Framework Overview of next three parts Scenario Generation Facility Evaluation Performance Summary Illustrative Analysis Capabilities 42 21

22 Performance Summary Procedure Analyst enters direction of travel and performance measure Travel time Travel speed Stop rate Running time Through delay Work day-by-day, analysis-period-by-analysis-period in chronologic order Mine performance measure from output file Compute summary statistics Average Standard deviation Skewness 10th, 80th, 85th, 95th percentile Base free-flow speed and travel time Step 3. Performance Summary 44 22

23 Step 3. Performance Summary Performance Measures By Direction EB/NB WB/SB By System Component Facility Segment By Performance Measure Travel time Travel speed Stop rate Running time Through delay Examples EB direction 45 Step 3. Performance Summary Facility Travel Time (s) PTI = 2.9 Note Maximum travel time 800 s Two crashes at same time but different intersections Planning Time Summary Statistics Scenario evaluation interval: 1 Average: th percentile: Base free-flow speed, mi/h: Standard deviation: th percentile: Base free-flow travel time, s: Skewness: th percentile: Median: th percentile: Number of obs.: th percentile:

24 Step 3. Performance Summary Facility Travel Speed(mi/h) Note 10 percent of analysis periods have LOS D, E, or F F E D C B A Summary Statistics Scenario evaluation interval: 1 Average: th percentile: Base free-flow speed, mi/h: Standard deviation: th percentile: Base free-flow travel time, s: Skewness: th percentile: Median: th percentile: Number of obs.: th percentile: Urban Streets Reliability Methodology Framework Overview of next three parts Scenario Generation Facility Evaluation Performance Summary Illustrative Analysis Capabilities 48 24

25 Illustrative Analysis Capabilities Alternatives Analysis Compare base condition to alternative condition Analysis Scenarios Work zones and special events Alternative start dates and durations Alternative lane closures and signal timing strategies Weather Examine operational effects of strategies that reduce weatherrelated crashes or crash severity (i.e., snow removal, resurfacing) Incidents Examine operational effects of strategies that reduce incident duration Evaluate benefit of providing shoulder for stalled vehicle refuge Design or Operation Evaluate alternative signal timing plans Evaluate intersection lane allocations or segment geometry 49 Closure Questions or Comments? 25