Presentation on theme: "Pavement Preservation and the Role of Bituminous Surface TreatmentsA Washington State View Minnesota Pavement Conference February 14, 2008 1."— Presentation transcript:
Pavement Preservation and the Role of Bituminous Surface TreatmentsA Washington State View Minnesota Pavement Conference February 14,
The Situation WSDOT policy, in essence, mandated use of BSTs for routes with an ADT < 2,000. Pavement preservation funding level (real dollars) is down. –Pavement preservation funding is a WSDOT account used to pay for contract HMA and BST projects. Questions –What is a reasonable ADT upper limit for application of BSTs? –What kinds of pavement performance can we expect if more BSTs are done and fewer HMA overlays? 2
3 WSDOT Pavements by Surface Type SurfaceLane Miles BST5,000 HMA11,000 PCC2,000 Total18,000
4 Preservation Policies and Practices SurfaceCommon PreservationComments Hot Mix Asphalt45-mm overlay year intervals most common All traffic levels All ESAL levels Bituminous Surface Treatment Single shot (application) BST 5-10 year intervals most common Lower traffic pavements AADT < 4,000 ESALs < 50,000/yr Portland Cement Concrete Either HMA overlay or dowel bar retrofit plus grinding Most over 30 years old Limited rehabilitation to date Most prevalent on NHS routes
FHWA IRI Thresholds for Interstate Highways DescriptionPSR Rating IRINHS Ride Quality Very Good m/km Acceptable (0-2.7 m/km) Good m/km Fair m/km Mediocre m/km Poor2.5>2.7 m/kmLess than Acceptable (>2.7 m/km) 6
Existing IRI Sorted by ADT ADT (2002)Average IRI (m/km) >=
8 WSDOT Pavement Preservation Funds Biennium Total Funds 1,2 Funds by Pavement Type 1,2 HMABSTPCCOther Average Note 1: Includes project engineering, construction engineering, safety, taxes. Note 2: Funds shown unadjusted for inflation.
Percentages of Pavement Preservation Funding by Type BienniumHMABSTOther %6%31% %6%17% %9%14% %7% %10%7% %18%12% %19%8% 9
10 Preservation Pinch
Preservation Funds by Lane-Mile per Year 11 BienniumOverall Funding Per Lane Mile Per Year 1,2 Preservation Funds by Pavement Type $/Lane-Mile/Year 1,2 HMABSTPCCP ,2007,6001,7006, ,50010,9001,9008, ,3009,2002,5006, ,9009,9001,8001, ,2008,5002, ,8006,7003,9004, ,8008,2004,8003,700 Averages ( ) 7,0008,7002,7004,300 Note 1: Funding shown includes project engineering, construction engineering, safety, and taxes. Note 2: Amounts shown not adjusted for inflation.
Initial Bottom Line Not enough funding to fully preserve the route system. Increasing use of BSTs in lieu of 45mm thick HMA overlayshowever overlays are still and will continue to be the preservation treatment of choice. How did we examine the efficacy of increased BST use? First, lets quickly look at HMA performance. 12
Quick look at HMA Overlay Performance Performance for more recent (post Superpave) projects –Rutting –IRI –Life by western and eastern Washington Projects placed between 1996 and 2001 –Evaluated with 2006 pavement condition survey –Pavement age: 5 to 10 years –½ inch HMA only –26 projects 13
Average Performance 14
17 HMA Overlay Life Pavement life is also a function of –Construction practices –Specifications –Material selection
18 $240,000 per lane-mile$21,000 per lane-mile
19 Key Question What is the effect on the WSDOT preservation budget? What is the effect on long-term network performance? What is the effect on the traveling public? Further –What is a reasonable upper level of AADT, at which BST resurfacings can be used? –What is a reasonable upper level of annual ESALs at which BST resurfacings can be used? –What combination of BST resurfacings and HMA overlays produce a cost effective rehabilitation strategy? Could we save money by using BSTs on some roads that are currently surfaced with HMA?
20 HDM-4 (v2.03) The Highway Development and Management System software Integrates multiple models in a unified analysis –Economic –Material –Structural –Condition UW and WSDOT has experience with HMD-4
21 Preservation Strategies Modeled HMA overlay only –Only apply 45-mm overlays to all sections –Triggers: 10% cracking, 10 mm rutting, 3.5 m/km IRI BST applications only –Only apply BST surfaces to all sections –Triggers: 10% cracking, 3.5 m/km IRI (no rutting trigger) BST and HMA treatment combination –Apply a combination of BSTs and HMA overlays to all sections –Triggers: BST: 10% cracking HMA: 3.5 m/km IRI For instance: 2 cycles of BSTs then 1 cycle of HMA overlay Open selection with any of the above three strategies –HDM-4 is free to choose for each individual section, which of the 3 above strategies to use
22 HDM-4 Modeling Observations Model may be biased towards existing trends The treatment strategy selected is highly dependent on the initial roughness The BST/HMA combination strategy is often selected regardless –Not able to fine-tune the BST effects enough The HDM-4 model schedules a large number of treatments in the first year HDM-4 is difficult to master HDM-4 software support is almost non-existent.
23 Preservation Strategy Comparison Scenario a Equilibrium IRI c (m/km) Net Present Value b HMA overlay only1.90$17,758 BST application only3.68$17,856 BSTs interspersed with HMA overlays triggered at 3.5 m/km IRI 2.72$18,170 Open selection2.96$18,187 Notes: a. Budget limitations are not used in triggering a resurfacing. b. All costs are in millions of present-day dollars. c. The IRI that a given scenario can maintain over time. ADT less than 8,000 and annual design lane ESALs less than 40,000
24 HDM-4 Estimated Roughness Conditions AADT less than 8,000 and annual design lane ESALs less than 40,000
25 HDM-4 Results The NPV of all strategies are the same –Increasing the use of BSTs appears to be economically feasible Agency expense and user costs increase over time for all strategies except the HMA overlay only option Reduced agency expenses will result in rougher pavements and higher user costs Higher BST use shifts cost from the agency to the user unless…
26 HDM-4 Conclusions HDM-4 is of limited but some use. Routes with AADT > 2,000 are viable for BSTs. Considering more BSTs is not a mistake. The cost of maintaining a road network is largely a zero-sum game.
Overall Assessment (1) Analyses via HDM-4 showed that more lane-miles of BST OK from a NPV view. ADT criterion increases from 2,000 to 4,000-5,000. –WSDOT Pavement Policy has been changed to reflect this. –And…there physically is no ADT limit for BSTs. More BSTs will likely increase the IRI on the route system but by a limited amount (cycles of BST/HMA overlays, level-up quantities, etc, limit IRI increases). BSTs will rarely be used through towns and cities or at major intersections. 27
Overall Assessment (2) Performance in Washington State –BSTs apparently exceed typical national stats. –HMA at or above national stats. Differences between western and eastern Washington need to be reduced. Does WSDOT need more pavement preservation funds? –Of coursebut how much? –Likely something close to $10,000/lane-mile/year. 28
Overall Assessment (3) Is WSDOT likely to get that much pavement preservation funding anytime soonNO. –So what can be done? –Tweak the mix of BST and HMA overlays (in progress). –Maximize quality of both hence performance life. –Monitor carefully via PMS. –Dont do anymore HDM-4 analyses! 29
Thanks for you attention Contributors include Steve Muench, UW and Linda Pierce, WSDOT 30 Questions?