French Engineering, LLC

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Work Zone Safety and Mobility Traffic Analysis
and Impacts

• French Engineering, LLC
• Greenhorne OMara, Inc.
• Pennsylvania Department of Transportation
• Bureau of Highway Safety and Traffic Engineering
• October 27, 2009

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Agenda

• Background Information
• DAWB Theory and Application to Freeway /
  Interstate Projects
• Questions on Traffic Analysis
• Lessons Learned / Group Discussion
• Course Wrap Up
• Text questions throughout

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Background Information
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State Survey and Background Work

• Five States Contacted
• Florida, Maryland, Michigan, Ohio, and Virginia
• Spreadsheets provided by 4 of 5
• Key Findings
• Quickzone only used for largest projects
• All states developed their own spreadsheets
• Ohio spreadsheet was foundation of the one
  developed for PA
• Estimating work zone capacity is usually weakest
  link in analysis
• Borrowed some FL methodologies for capacity
  estimation

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Overview of Delay Computation Methodology

• Identify Critical Activities from a Traffic
  Capacity / Bottleneck Point of View
• Develop Approach Based on Available Tools, Data,
  and Need for Multi-Period Analysis
• Execute Approach

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Importance of Analysis Period

• Undersaturated, Uncongested Scenarios
• Single Period of Analysis May Be Sufficient
• Available Tools are Many
• Oversaturated, Congested Scenarios
• Multi-Period Analysis May Be Required
• DAWB Spreadsheets In Conjunction with Other
  Programs
• Other Programs Exclusively if Precision is
  Required

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Delay Analysis Workbook (DAWB) Theory and
Application
P\bhste_shared\workzones\WZ traffic analysis
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Overview of DAWB

• 6 Spreadsheets Contained Within
• Capacity Estimation
• Bottleneck Analysis
• Quick Bottleneck Analysis
• Existing Bottleneck Analysis
• Two-Way One-Lane Not to be discussed today
• Detours Not to be discussed today
• Can Be Used as Standalone or With Other Programs
• Key is Estimate of Capacity and source of demand
  information
• Designed for Easy Multi-Period Analysis

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Capacity Estimation Spreadsheet
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Overview

• Tools and science available to estimate work zone
  capacity are expected to improve in the future
• Spreadsheet is designed to provide the user with
  some guidance for the selection of a capacity for
  the work zone
• Three tools provided
• Freeways
• Two-Way One-Lane Work Zones
• Other Facilities
• Only Freeways will be discussed today
• Other tools (or experience) may provide better
  estimates

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Freeways (HCM Chapter 22)

• Short-Term Work Zones
• Capacity (1600 I) fhv N R
• Where
• Capacity adjusted mainline capacity (vph)
• I adjustment factor for type, intensity, and
  location of work activity (ranges from 160 to
  -160 pcphpl)
• R adjustment for on-ramps in the taper or
  within 500-ft downstream of the beginning of the
  full lane closure
• R should be made equal to the ramp volume, not to
  exceed half the capacity of one lane
• Nnumber of lanes open through the short-term
  work zone
• fhv heavy vehicle factor

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Freeways (HCM Chapter 22)

• Long-Term Work Zones
• Summary of Capacity Values for Long-Term Freeway
  Work Zones

Notes If crossovers are used, the capacity is
close to the value 1,550 vphpl If no crossover
is needed, but only a merge down to a single
lane, the value averages to 1,750 vph
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Freeways (HCM Chapter 22)

• Lane Width Considerations
• Capacity decreases 9 when lane widths drop from
  11-ft to 10-ft
• Capacity decreases 14 when lane widths drop from
  11-ft to 9-ft
• Capacity decreases could be greater with the
  influence of trucks

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Example

• Short-term freeway closure with no ramps but a
  very active work zone. One (of two) lanes to
  remain open. Level terrain and 5 trucks.

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Example Solution Hand Calcs
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• Solution (HCM)
• Capacity (1600 I) fhv N R
• I -160 R 0 ET 1.5 PT 5 N1
• fhv 1 / 10.05(1.5 1) 0.976
• Capacity (1600 -160) 0.976 1 0
• Capacity 1405 vph, rounded to 1400 vph

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Example Solution in DAWB
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Quick Bottleneck Analysis Spreadsheet
USE BOTH LANES TO MERGE POINT
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Quick Bottleneck Overview

• Intended for use when
• Only AADT and work zone capacity are known
• Work zone capacity is somewhat constant
  throughout the day
• Daily Commuter Route
• Performs queuing and delay analysis based on
  cumulative arrivals and departures versus time
• If more volume information is known, weekend
  peaks are critical, or capacity is highly
  variable, use Bottleneck Analysis Spreadsheet.

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Queue / Delay Model
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Spreadsheet Inputs

• One Way Work Zone Capacity
• Average Annual Daily Traffic (AADT)
• Percent of Peak Period (gt1000 vph) Traffic
  Diverted ()
• Number of Lanes for Queued Vehicles (lanes)
• Percent Trucks (Daily)
• Traffic Pattern Group (TPG) (Number 1 to 10)
• http//www.dot7.state.pa.us/itms/main.htm
• Inbound 1, Outbound 2, Neutral 3

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Spreadsheet Outputs

• Number and Duration of 15-Minute Delay Episodes
• Number and Duration of 30-Minute Delay Episodes
• Total Daily Delay
• Queue Length (in vehicles and miles) at the End
  of Each Hour
• Delay for the Last Vehicle of Each Hour

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Example 1Analysis of Freeway Lane Closure /
Restricted Typical Section Using AADT and TPG
Information
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Overview of Example

• One of the two existing lanes is to be closed on
  I-70 / I-79 Eastbound in Washington County
  upstream of the south junction
• Perform quick analysis using information from
  PennDOT ITMS website and minimal other
  information
• Use Capacity Estimation and Quick Bottleneck
  Analysis spreadsheets

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Location Map
PROJECT LOCATION
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PennDOT Video Log
http//www.dot7.state.pa.us/ividlog/video_locate.a
sp
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PennDOT ITMS Information
http//www.dot7.state.pa.us/itms/main.htm
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Capacity Estimation
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Quick Bottleneck Analysis Inputs
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Quick Bottleneck Analysis Outputs
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Quick Bottleneck Analysis Outputs (Continued)
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Example Conclusion

• Proposed closure would have sustained 15-minute
  delays lasting more than two-hours as well as
  30-minute delays
• Significant Project
• Remember
• Volume estimation off hourly distributions from
  Table 350 in Traffic Data Report. Update to
  2008 edition!
• Actual volumes will likely provide better results.

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Bottleneck Analysis Spreadsheet
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Overview

• Use when
• Actual hourly volumes are available
• Capacity varies by the time of day
• Facility is not an existing bottleneck
• Outputs and computations are identical to those
  in Quick Bottleneck Analysis Spreadsheet
• Inputs are same except
• One-Way Annual Average Daily Traffic (AADT),
  Traffic Pattern Group and Direction, and One-Way
  Capacity are omitted
• Hourly volumes and capacities are directly input

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Example 2I-70 Fulton CountySingle Lane Closure
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Overview of Example

• I-70 Eastbound between Breezewood and Maryland
• Long project 14 miles Crosses mountain ridge
  and has three interchanges and a rest area
• One week of hourly traffic data collected in
  August 2008 available
• Traffic queue and volume information from similar
  lane closures on the westbound side

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Location Map
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Project Location
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Key Issues
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• Traffic peaks on the weekends. Average weekdays
  are significantly different from Friday through
  Sunday, and are not critical.
• Estimation of capacity from similar work on
  westbound side.
• Queuing and delay expected based on experience in
  westbound direction.

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Traffic Volumes
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Volumes Estimated from AADT TPG
Actual Sunday Volumes
Actual Friday Volumes
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Hourly Traffic Volumes
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Estimation of Capacity
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• EB and WB traffic was converted from vehicles
  to passenger car equivalents to account for
  differences in grade and truck .
• Known WB queue was 2 miles in the Friday
  afternoon peak.
• Actual WB PCE volumes were input in Bottleneck
  Spreadsheet.
• Capacity adjusted until known queue length
  resulted.
• Resulting capacity was 1300 PCE / hour
• EB analysis was then conducted using PCE volumes
  instead of actual volumes

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Spreadsheet / Analysis of Westbound Direction For
Determining Capacity
1300 PCE Capacity
2 mile backup
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Eastbound Analysis SpreadsheetsFridaySaturdayS
unday
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FRIDAY ANALYSIS
No delays or queues expected
PCE Volumes Input
1300 PCE Capacity
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SATURDAY ANALYSIS
Again, no delays or queues expected
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SUNDAY ANALYSIS
Major Delays and Queues Expected
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Example Conclusions

• No delays on days Monday through Thursday
• Friday had delays in the westbound direction but
  not eastbound
• Eastbound had significant delays on Sunday
• For an interstate / intercity route summertime
  weekend traffic data are key

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Example 3Oversaturated Ramp to a Freeway Work
ZoneVariable Capacity Problem
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Overview of Example
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• An interchange lies within a freeway work zone
  that is oversaturated. The off-ramp is upstream
  of the on-ramp.
• The interchange volumes are shown on next slide.
  The off-ramp volume will be the capacity for the
  on-ramp traffic flow.
• Perform a variable capacity problem using the
  "Bottleneck Analysis" worksheet

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Interchange Traffic Volumes
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Bottleneck Spreadsheet Inputs
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Delay Outputs
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Example Conclusion
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• Significant delay on the on-ramp.
• There are individual delays gt 50 min
• Delays gt30 min sustained for more than two hours
• The delay on the ramp could be greater than the
  delay on the mainline at the entrance to the work
  zone.
• Variable capacity problem also applies to work
  zone time restrictions

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Existing Bottleneck Analysis Spreadsheet
Squirrel Hill Tunnels, Pittsburgh
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Overview

• Modification of Bottleneck Analysis spreadsheet
  
• Need hourly volume and capacities are available
• Also need normal capacities, which are presumed
  to result in some existing over-capacity
  conditions
• Outputs and overall methodology are the same as
  the Bottleneck Analysis spreadsheet except
  delay measures focus on added delay relative to
  existing delay

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Area of Spreadsheet to Input Normal Capacity
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I-70 Sunday Example Data with Arbitrary Normal
Capacity
Delays are slightly less than before since some
is attributed to existing bottleneck
Normal Capacity input here
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Traffic Analysis QuestionsDiscussion
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Lessons Learned
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From Personal Experience

• Differentiate between commuter traffic patterns
  and interstate / intercity patterns
• Importance of representative traffic data
• Capacity estimation from observation of similar
  projects

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Group Discussion of Lessons Learned

• Central Office
• District
• Consultant

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Final Questions Wrap - Up