Title: Pavement Preservation and the Role of Bituminous Surface TreatmentsA Washington State View
1Pavement Preservation and the Role of Bituminous
Surface TreatmentsA Washington State View
Rocky Mountain Asphalt Conference
February 20, 2009
2The Situation
- WSDOT policy, in essence, mandated use of BSTs
for routes with an ADT lt 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?
3WSDOT Pavements by Surface Type
4Preservation Policies and Practices
5WSDOT Lane-Miles by ADT
42
6FHWA IRI Thresholds for Interstate Highways
7Existing IRI Sorted by ADT
8WSDOTPavement Preservation Funds
Note 1 Includes project engineering,
construction engineering, safety, taxes. Note 2
Funds shown unadjusted for inflation.
9Percentages of Pavement Preservation Funding by
Type
10Preservation Pinch
11Preservation Funds by Lane-Mile per Year
Note 1 Funding shown includes project
engineering, construction engineering, safety,
and taxes. Note 2 Amounts shown not adjusted for
inflation.
12Initial 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.
13Quick 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
14Average Performance
15Rutting
16Ride
17HMA Overlay Life
- Pavement life is also a function of
- Construction practices
- Specifications
- Material selection
18240,000 per lane-mile
21,000 per lane-mile
19Key Question
Could we save money by using BSTs on some roads
that are currently surfaced with HMA?
- 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?
20HDM-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
21HDM-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.
22HDM-4 Estimated Roughness Conditions
AADT less than 8,000 and annual design lane ESALs
less than 40,000
23HDM-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
24HDM-4 Conclusions
- HDM-4 is of limited but some use.
- Routes with AADT gt 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.
25Overall 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. - Andthere 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.
26Overall 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.
27Overall 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!
28Thanks for you attention
Questions?
Contributors include Steve Muench, UW and Linda
Pierce, WSDOT