WSDOT/UW Road Roughness Study: WSDOT/UW Road Roughness Study Research Study By: Kevan Shafizadeh University of Washington Presented By: N. Sivaneswaran (Siva) Pavement Management Engineer Washington State Department of Transportation


Study Motivation: Study Motivation A 1997 telephone survey of 508 Washington adults ranked “poor road surface/potholes/ruts” as the second biggest problem with Washington interstates (second only to congestion/inadequate capacity) Source: Washington State’s Joint Legislative Audit and Review Committee (JLARC) Over $400 million of the state transportation budget is devoted to highway maintenance and preservation each year.


Study Characteristics: Study Characteristics WSDOT sponsored research conducted by University of Washington Identify factors that affect the public’s perception of road roughness Identify “acceptable ride quality” thresholds When should a pavement be rehabilitated due to roughness?


Pavement Roughness Thresholds(Interstate Facilities): Pavement Roughness Thresholds (Interstate Facilities) Source: Federal Highway Administration (FHWA), 1999.


WSDOT IRI Determination: WSDOT IRI Determination High speed profiler Travels at posted speed Conducted annually All state highways Both directions on divided highways One direction on simple two way


Study Details: Study Details Phase I: Customer Survey Mailout-Mailback Survey General “customer satisfaction” Phase II: In-Vehicle Study 40 road segments I-5, SR-520, I-90, and I-405


Phase I: Customer Survey: Phase I: Customer Survey General opinion about roughness, road quality issues around Seattle area Collected individual socio-demographic information Gender, Age, Income, Education, etc. Willingness to participate in a driving experiment?


Phase I: Customer Survey: Phase I: Customer Survey License plates were recorded of vehicles entering and exiting SR-520 near UW Surveys were mailed out to individuals through the WA DOL with return postage Completed surveys were mailed back to UW


Phase I: Customer Survey: Phase I: Customer Survey Over 2,800 license plates collected (Fall 2000) 2,570 surveys mailed to registered owners (Winter 2000) 529 Valid Surveys Returned 173 Valid Surveys with Contact Info


Phase I: Customer Survey: Phase I: Customer Survey General “customer satisfaction” information obtained from Seattle-Area commuters Note: Results based on 1-5 scale where 1 = excellent, 3= average, and 5 = poor.


Summary Statistics: Gender: Summary Statistics: Gender


Summary Statistics: Income: Summary Statistics: Income


Summary Statistics: Age: Summary Statistics: Age


Summary Statistics: Education: Summary Statistics: Education


Phase II: In-Vehicle Surveys: Phase II: In-Vehicle Surveys Individuals were surveyed for their perceptions of roughness while driving on 40 local freeway segments, controlling for: In-Vehicle Noise Vehicle Type Vehicle Speed Pavement Type Start Location Weather Conditions Roughness (IRI)


Phase II: Segment Selection Criteria: Phase II: Segment Selection Criteria Freeway segment in Seattle study area that: Is easily and safely traversable by drivers of varying abilities and in a reasonable amount of time (< 2 hrs) Has consistent and homogenous attributes Same Surface Type Same Geometric Design (# of Lanes, Shoulder Widths) Same Terrain Similar IRI Is separated by distinguishable and has easily identifiable features Corresponds to locations where physical indices have been documented (Washington State Pavement Management System (WSPMS)) Samples a range of IRI values


Study Vicinity: Study Vicinity


Study “Loop”: Study “Loop” University Village Eastgate P&R


Summary of IRI Measurements: Summary of IRI Measurements


In-Vehicle Participants: In-Vehicle Participants 56 individual drivers 2240 driver-segments observations Four different vehicle types Midsize sedan - KIA Optima (18 participants – 32%) Sport utility – Jeep Grand Cherokee(16 participants – 29%) Pickup – Ford Ranger(12 participants – 21%) Minivan – Ford Windstar(10 participants – 18%)


Results: Roughness Rankings vs. IRI: Results: Roughness Rankings vs. IRI


Results: Roughness Rankings vs. IRI: Results: Roughness Rankings vs. IRI


Roughness Ranking vs IRI: Roughness Ranking vs IRI 1 2 3 4 5 Mean Perceived Roughness Ranking 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Measured IRI (m/km) Mean Rank by Drivers (1=smooth, 5=rough) Measured IRI (m/km)


Roughness Ranking vs IRI(elevated segments): Roughness Ranking vs IRI (elevated segments) 1 2 3 4 5 Mean Perceived Roughness Ranking 0 50 100 150 200 250 300 Measured IRI (in/mi) Roughness Rankings on Elevated Segments Roughess Rankings on Non-Elevated Segments Measured IRI (in/mi)


Roughness Ranking vs IRI (by pavement type and elevated segments): Roughness Ranking vs IRI (by pavement type and elevated segments) 1 2 3 4 5 Mean Perceived Roughness Ranking 0 50 100 150 200 250 300 Measured IRI (in/mi) Roughness Rankings on PCCP Segments Roughness Rankings on ACP Segments Measured IRI (in/mi) Roughness Rankings on Elevated Segments


Acceptability Thresholds: Acceptability Thresholds


Acceptability Thresholds: Acceptability Thresholds


Acceptability Thresholds: Acceptability Thresholds


Results: Statistical Models: Results: Statistical Models


Study Conclusions: Study Conclusions IRI does not fully capture driver’s perception of roughness, but it remains a very significant indicator Acceptable thresholds, based on IRI, can be identified Other important indicators Partial slab replacement Expansion joints Studded tire wear


State Trigger Values (1998): State Trigger Values (1998) * Criteria dependent on highway type


2002 IRI Statistics: 2002 IRI Statistics


Additional Questions: Additional Questions Are smoother pavements lasting longer? What IRI value shows improved pavement performance? What IRI value should be used as a smoothness specification? How should bonus/penalty be accessed?


Research Report: Research Report Shafizadeh, K., F. Mannering, and L. Pierce (2002). A Statistical Analysis of Factors Associated with Driver-Perceived Road Roughness on Urban Highways, Washington State Transportation Research Center. Research Report. WA-RD 583.1. June 2002. (http://depts.washington.edu/trac/bulkdisk/pdf/538.1.pdf)