Pavement Preservation Journal - Spring 2012 - (Page 17)

Deck Micro Surfacing Cuts Accidents, Wins Award by Thomas J. Wood The use of micro surfacing has been a cost effective method to reduce wet weather accidents in this case. from an estimated ADT of 33,000 in 1988 to an ADT of 54,000 in 2009. However, wet weather crashes and total crashes decreased by 76 percent and 19 percent respectively after the placement of micro surfacing. In looking at cost-effectiveness, MnDOT calculates an average cost of $70,000 for all crashes and an average construction cost of $2.30 per square yard for single course micro surfacing. Using these figures, the wet weather crash reduction has a payback ratio of 14:1 for every dollar spent. Local maintenance forces re-applied the micro surfacing after five years to insure high friction characteristics. If the time between reapplication is lengthened to seven years, the payback ratio becomes 19.7:1. These analyses show that the use of micro surfacing was a cost-effective method for reducing wet weather crashes. During this 20-year period, the combined ADT for both directions rose from the estimated ADT of 33,000 in 1988 to an ADT of 54,000 in 2009. This is a 65 percent increase in daily traffic, yet the rate of wet weather crashes fell by 76 percent and total crashes by 19 percent after the placement of micro surfacing on the bridge decks and approaches. Using a student’s t-test, this change is statistically significant to a 95 percent confidence interval. The cost-to-benefit ratio is the following: the wet weather crash reduction has a payback ratio of 14:1 for every $1 spent, and if you lengthen the time between re-application to seven years, which is the normal application time for lower volume roadways, then the payback becomes 19.7:1. The data clearly show that the use of micro surfacing has been a cost effective method to reduce wet weather accidents in this case. Wood is research project supervisor, Mn/DOT Office of Materials & Road Research, Maplewood, Minn. Brad Estochen and Nathan Drews of Mn/DOT’s Office of Traffic, Safety and Technology are gratefully acknowledged for supplying accident data. Spring 2012 pavement preservation journal 17 Receiving National Roadway Safety Award in November 2011 on behalf of the Minnesota DOT is, center, Thomas J. Wood; he is flanked by Greg Cohen, executive director, Roadway Safety Foundation (left) and John Porcari, deputy secretary, FHWA T he use of micro surfacing on bridges is a cost effective method of preventive maintenance that reduces both wet weather crashes and crashes in general, research by the Minnesota DOT shows. It’s expected that this method is a viable option to further improve bridge safety conditions in Minnesota. These fi ndings were so significant that in November the study was a winner in the biennial National Roadway Safety Awards, sponsored by the Roadway Safety Foundation and the Federal Highway Administration. Historically, the I-94 bridges east of Monticello, Minn., had a higher crash rate than the surrounding highway. The elevated rate could, in part, be attributed to poor geometry. The bridges were on a super-elevated curve over a railway. In addition, the elevated bridge decks allowed the concrete deck to cool off faster than the surrounding pavement, causing bridge decks to become icy at a faster rate than the surrounding pavement. In 1999, MnDOT applied its fi rst-ever micro surfacing treatment to the bridges and approaches. The bridges were included to evaluate micro surfacing’s effectiveness of reducing both wet weather and typical crash rates. The plan was to use MnDOT’s/International Slurry Surfacing Association Type III aggregate gradation, which is well graded with 100 percent passing the 3/8-in. sieve. MnDOT analyzed crash data for the 10 years both before and after the application to determine the effectiveness of micro surfacing on reducing wet weather crash rates. Over a 20-year period, the combined average daily traffic (ADT) for both directions rose 65 percent, http://www.naylornetwork.com/fpp-nxt

Table of Contents for the Digital Edition of Pavement Preservation Journal - Spring 2012

President’s Message
National Preservation Conference: Make Plans Now
Pavement Preservation is ‘Sustainable’ Choice
Deck Micro Surfacing Cuts Accidents, Wins Award
Enhanced Fog Seals Boost Chip Retention
Sophisticated ‘Seal Coats’ Enhance Texas DOT Pavement Preservation
Rejuvenating Treatment Preserves Runway, Grooving
Fine-Mill Pavements for Smooth Thin Overlays
Puerto Rico, Southeast States Focus on Preservation
Maryland Identifies Right Fix for Right Road, Right Time
‘Thin is In’ for New Texas Center Courses
Why to Cut Back on Cutback Asphalt
Test Sections Constructed at Virginia Smart Road
Ground Penetrating Radar Fills Gaps in PMS

Pavement Preservation Journal - Spring 2012

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