3. As MnDOT invests in building
bigger and safer bridges to
accommodate future growth in Metro
area….
Question: What are the most effective
solutions available to reduce weather
related crashes?
10. Project Level Risk Assessment Tool
In 2012, MnDOT Risk Assessment Review
Team agreed upon the following GOAL:
“Anti-icing systems or services are
common sense and environmentally sound
strategies that result in greater safety
while cost effectively managing ice issues
without shortening the life of bridge
structures and roadway investments'.”
Anti-icing is a supplement to S&I operations…
Proactive timely response to slippery conditions
Effective @ preventing successive crashes
Helps MnDOT meet Toward Zero Death vision
Spinouts on I-35 at Hwy 8 …Jan 30, 2014
Truck Stations Supervisors will have to make split second decisions in the future about priorities:
Can they afford to continue to brake-off a crew of snow plow trucks during rush hour to specially
Treat a bridge deck that is reported to be icy and under stop and go traffic conditions?
All suggested solutions are supplement to S&I operations.
Sometime, If we do nothing…the bridge may be safe and efficient
Steeper profile grade and curves in horizontal alignment are safety concerns
Chip seal will help provide high friction pavement…Tried once in Minnesota & It wears away when S&I truck remove snow
Instead of coring holes in Bridge deck for spray nozzles….other options area available too; spray nozzles installed in on/off ramps…parapet sprayers….curb sprayers….
Embedded electrical cables or pipes containing heated fluid….thermal deicing
Drivers’ Ed and Advance warning flashers intent is to modify driver’s behavior
And expectations (ideally all drivers will respond with lower speed under icy conditions)
Anti-icing is one of the tools in our tool box to provide safety and reduce environmental impacts
Potassium Acetate: Delivered as a liquid. Used on automated bridge anti-icing systems.
Non-corrosive. Biodegradable alternative for areas where chloride use must be limited.
Higher cost per gallon compared to sodium chloride.
Lowest practical melting temp. -30 degrees F
Concentration 50%
CF7 cost $4.5 per gal. Chloride cost $1.0 per gal.
With Poor workmanship....DOT will pay heavy price in the future maintenance cost
Stop ice formation and prevent snow compaction
Types of installations; roads…ramps…loops…bridges
Anti-icing systems could be: holes in Bridge deck or bridge parapet or curb installation or ramps & loops approach bridge deck.
Benefit/cost ratio
Preliminary cost estimate
Type of bridge is not a factor in deciding go or no go
St. Anthony Old Bridge before collapse had an anti-icing system
Installed for 9 years w/o issues to concrete or steel.
Eng. Services Is committed to provide operation and maintenance after the installation of future systems
Systems should be kept working all year around to avoid plugging and corrosion problems
Warnings for overfill and low level chemicals in storage tanks
Warnings for potential leak and that where usually the system
Is designed to shut down
Here is the overall GOAL…..
Project Level Assessment Tool
MnDOT have a well documented procedure for selecting locations to install anti-icing
Put together by team of MnDOT experts in 2012 (maint….bridge…env. Office) to help
Mitigate any future risks
Define each Risk and assign grade to Its impact on MnDOT GOAL
Then assess the probability or likelihood of vehicle needing to come to a stop from high speed
And come up with a final score.
Safety…Operation & Maintenance….Structure Deterioration (all risks will discussed by stakeholders in a collaborative meeting lead by PM)
Weather sensors/stations….pump house….storage tanks…..power/comm. Equipment….
controller……spray nozzles…. Valves….plumbing (electrical/anti-icing chemical)
RWIS = Road Weather Information System
FAST = Fixed Automated Spray Technology
Potassium Acetate: chemical used for anti-icing…very expensive….less corrosive than Sodium Chloride and biodegradable
Chemical is compatible with stainless steel, aluminum and cast iron (2009 – Journal of Civil, Environmental, and Architectural Engineering)
Volume 3, Issue 1.
Potassium Acetate has been used since the early 1990s at airfield pavements (runways, and taxiways) due to concerns about the corrosiveness
Of Chlorides. It is safe to say that potassium acetate can exacerbate ASR-induced expansion and cracking. (Sept 2008 – Technical Report about The Effects of Potassium Acetate De-Icing Chemicals on the Performance of Concrete Containing Fly Ash)
RWIS and sensors measure pavement and atmospheric conditions to determine the optimal time to activate anti-icing system.
Pump stations will activate spray nozzles.
Spray programs are established for frost, freeze, and snow conditions.
MnDOT had track record of success with crash reduction on TH 35W smart Bridge and Lexington TH 35E Bridge.
In both cases the number of accidents after bridge construction is lower than historical accidents records.
Safety analysis of CDOT’s FAST system (October 2014)…an estimated crash reduction in urban interstates.
I-35W & Mississippi River Bridge Anti-icing Evaluation Report (July 2001)….crash reduction during winter 1994 – 2001
Evaluation of North Dakota’s Fixed Automated Spray Technology System (October 2009)….study for two FAST systems…The Buxton Bridge system
In March 24, 2014…61 cars were involved in Mendota Bridge Crash….
Two vehicles lost control…a semi jack-knifed. Sixty one cars after
The jack-knifed semi then pulled into each other.
Environmental Benefits:
Chemical used is biodegradable and dissipates in two weeks
More Efficient and effective than traditional maintenance operations
Non-toxic the environment/wildlife or humans
MnDOT maintenance understands what it takes (operations & maintenance) to keep these systems running.
Metro Maintenance have eight (8) anti-icing systems currently on Bridges / Roads / Ramps.
Engineering Services and Bridge Maint. Crews gained valuable expertise in the last fifteen (15) years.
Anti-icing is a supplement to S&I operations…
Proactive timely response to slippery conditions
Effective @ preventing successive crashes
Since MnDOT don’t have the ability to respond to icing in all cases to prevent crashes
That will impact TZD (Toward Zero Deaths) vision to create safe roadways.
Please check the following handouts:
Anti-icing Selection process
Benefits…Issues…Lessons Learned (Anti-icing)
Share with Audience Handouts about Selection Criteria and Benefits & issues
