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High Friction Surface Treatment (HFST) has been used widely across the US to treat road departure crashes at horizontal curves with wet road conditions as a contributing factor. However, South Dakota has five times more roadway departure crashes involving winter road conditions than wet road conditions, and discovered that HFST had not been tested as a treatment for this crash type. Moreover, one third of roadway departure crashes occur on horizontal curves, even though horizontal curves account for less than 10 percent of the system.
A one-mile section of US 25 in Greenville County had been a cause for concern for the South Carolina Department of Transportation (SCDOT) for many years. Located in rural, mountainous terrain, and often subject to inclement weather including rain, snow, ice, and fog, US 25 carries traffic on two lanes in each direction and is separated only by a damaged and brittle concrete barrier. US 25 changes dramatically, from a relatively straight road in North Carolina directly to this particular section in South Carolina with horizontal and vertical curves and a 6 percent grade. US 25 has a speed limit of 55 mph and carries approximately 10,000 vehicles per day with heavy truck traffic.
SCDOT discovered a number of factors contributing to the high crash rates along this short section of US 25. One significant factor was that the concrete barrier's design did not allow for proper drainage, channeling water to the driving lane and shoulder. Speeding, inadequate pavement superelevation, and sight distance constraints also contributed to the safety issues at this location.
In 2000, SCDOT considered funding a major reconstruction project which involved replacing and updating the barrier wall and modifying the roadway's superelevation and drainage structures. However, with the project's estimate coming in at nearly $5 million, this project was unlikely to happen. Both costly and lengthy, the overall project development timeline for this alternative would have spanned approximately three years, and would have involved an extensive work zone and detour which would have inconvenienced local residents and drivers traveling through this area.
Over the years, low-cost measures of additional signing and markings were added along US 25, but these did not adequately address the excessive speeds and drainage issues, and the resulting safety improvement was minimal at best. At one point, a dynamic message sign (DMS) was installed to display a regulatory 45 mph speed limit during rainy conditions. However, due to the rural nature of this road segment and the wide road template, speeds remained excessive.
In 2008, a High Friction Surface Treatment (HFST) was applied to this curvy stretch of US 25. SCDOT had used this pavement treatment on ramp segments to increase skid resistance in locations where friction demand was high, but this one-mile project was the largest application to date, and at the time, it was unclear whether HFST would mitigate the hydraulic issues drivers experienced on this segment. With the planning process and installation complete in approximately six months, the HFST project cost SCDOT $1 million, which was 80 percent less than the previously considered reconstruction project.
A before and after study evaluating the HFST project's success on US 25 revealed significant safety benefits, with a 68 percent reduction in wet crashes and a 56 percent reduction in total crashes. Six years after HFST installation, SCDOT reports the pavement treatment is holding up very well, considering the high exposure to snow plowing.
To develop its current HFST specification, SCDOT used the AASHTO specification as the base model and integrated pieces from other States' specifications as well as their own experiences with the treatment. While their HFST specification is still evolving, SCDOT believes it strikes a good balance between quality materials and application, while still maintaining reasonable contractor expectations and competitive bidding.
Citing a before and after study of seven HFST project locations, SCDOT experienced an 81 percent reduction in wet crashes and 71 percent reduction in total crashes. Since HFST has proven to be a very cost-effective safety countermeasure, SCDOT has installed 20 HFST projects, with approximately 20 more locations planned for 2015. Widespread deployment will be incorporated once the DOT identifies the horizontal curves throughout the State. The benefit/cost analysis for these locations has proven HFST to be a very cost-effective countermeasure.
Northern California, near the Oregon State line is home to the Redwood National and State Parks, which span over 200 square miles and are some of the most environmentally diverse areas in the United States. Accordingly, transportation construction projects that disturb existing conditions within the parks' limits are subject to stringent environmental restrictions and long permitting processes.
Background
Over the last decade, a horizontal curve within the parks' limits experienced a high frequency of wet crashes. This curve, shown in Figure 1, is located on US 199, a two-lane, rural highway in Del Norte County, approximately one mile east of the South Fork Road intersection. It has a radius of 280 ft. and an advisory speed of 30 miles per hour (mph). Between 2006 and 2009, this site experienced 26 wet crashes and exhibited total and severe (fatal + injury) crash rates that were 7.3 and 4.3 times, respectively, greater than the statewide average for similar facilities. Crash types included run off road, head-on, and opposite direction sideswipe.
Figure 1. US 199 in Del Norte County
Caltrans previously installed several low-cost safety countermeasures at the site including center line rumble strips, speed warning signs, double stacked chevron signs, and one inch open grade asphalt concrete (OGAC) overlay. Yet, these treatments did not lead to the crash reductions Caltrans desired. They began to consider larger scale countermeasures, specifically roadway realignment. However, the realignment process would require a lengthy environmental review and mitigation of wetland impacts before the improvement could begin reducing crashes. As an alternative to realigning this curve, Caltrans began to investigate a High Friction Surface Treatment (HFST) and looked to other States for guidance and successes.
Factors Affecting the Final Decision
Figure 2. Threatened Species
Most critical for Caltrans at this location was mitigating environmental impacts. US 199 parallels the Smith River, the most pristine and environmentally sensitive river in California, protected by a full spectrum of environmental entities and regulations. The surrounding area sustains California's most diverse ecology, including the Marbled Murrelet and Northern Spotted Owl, as shown in Figure 2, both threatened species protected by the Federal Endangered Species Act. The area also contains over 400 separate species of plant life and a large number of active, very small wet lands.
Due to endangered species and water quality concerns, a roadway realignment project within the parks' limits would require Caltrans to spend six months acquiring environmental permits. Further, the North Coast Regional Water Quality Control Board requires Caltrans to mitigate construction effects upon the wetlands, even when impacts are only a few square feet. Wetland and impervious area mitigation ratios can range from 1:1 to 1:4 depending on several factors. If the replacement is to take place within another roadway project, it could be years before Caltrans is able to begin work on the initial project as crashes continue to occur. In contrast, HFST environmental impact and associated review is minimal and requires only a Categorical Exemption/Exclusion (CE/CE) document. HFST's nominal effect on the surrounding environment is due to the treatment's application between existing pavement edges, resulting in no net increase of impervious areas within the Parks limits.
In addition, any geometric improvement that involves construction incurs time restrictions (i.e., environmental windows) aimed at not disturbing wildlife. This would force Caltrans to either perform large-scale construction projects in stages or to use an accelerated/restricted schedule, both of which have significant effects upon the project. Conversely, HFST has the distinct advantage of an installation time period of just 10 working days.
HFST could be implemented quickly compared to alternatives, satisfying Caltrans environmental concern, construction time schedule, and window of opportunity.
Lastly, a feasible detour route for the realignment is not available because a network of local county roads that connects the lower and upper portions of the county does not exist. A detour around US 199 could take longer than 8 hours, which is estimated to cost upwards of $450 million a year in associated economic losses. HFST can be installed one lane at a time and therefore does not require a detour at any point during construction.
Table 1 summarizes and compares each countermeasure's environmental review and design time frames, construction duration, costs, and need for a detour.
Table 1. Comparison of Factors between HFST and Curve Realignment on US 199
Selecting HFST
In summer 2012, Caltrans opted for the simpler, but still very effective, alternative. They installed 850 ft. of HFST at this horizontal curve on US 199, shown in Figure 3. The treatment consisted of a double layer of epoxy-resin binder with calcined bauxite aggregate, which filled in the surface voids from the previously installed OGAC and added protection against water penetration. With a peak hour volume of approximately 600 vehicles per hour (vph), Caltrans estimated only a 5 minute travel time delay during active construction. Caltrans is unaware of any crashes at this location since the HFST implementation.
To date, 139 sites on State maintained roadways in California have received HFST or will receive the treatment in the near future. Caltrans continually encourages and tries to educate its districts about the benefits of HFST. The agency believes that HFST is one of the best tools in its toolkit for challenging curves and should be the primary “go-to” friction enhancing countermeasure, even before OGAC.
Figure 3. US 199 HFST Application Area
What criteria does Caltrans use to install HFST?
Caltrans believes HFST is an appropriate safety countermeasure for both wet and dry locations, high and low volume roadways, and tangents as well as curves. It is effective at mitigating crashes involving large changes in speeds (acceleration/deceleration), low skid numbers, tight horizontal curves, and roadway departure. As a result, Caltrans has implemented HFST on a large variety of locations including horizontal curves, bridges, wet crash locations, signalized intersections, on- and off-ramps, and short freeway segments.
Are there any locations where HFST is not appropriate?
Caltrans does not apply HFST in cold/icy locations where heavy trucks frequently use chains in winter, as the chains significantly decrease HFST's lifespan. Further, in long tangent sections with intense rainfall, OGAC is preferred.
Describe the roadway safety situation or state before the new practice was implemented. What was the safety issue, problem, or gap?
Presently, over half of the fatal and severe injury crashes in the Tampa Bay region occur on locally owned and maintained roadways. Traditionally, the Florida Department of Transportation (FDOT) has typically spent less than 10 percent of their allocated Federal safety funds on local roads. To aggressively address these fatal and severe injury crashes using a data-driven process, the District 7 (Tampa Bay region) office of FDOT developed and implemented the Local Agency Traffic Safety Program. The program is a coordinated and comprehensive effort to put the available safety dollars to use in reducing deaths and serious injuries on the roadways in the region.
What were the key challenges that needed to be addressed before the new practice could be implemented?
Prior to initiation of the program, the following challenges to allocating safety funding to the local agencies were identified:
Many of the local agencies did not have staff with specialized knowledge or training in traffic safety;
There was a general lack of knowledge among many of the local agencies about the available federal and state programs and the requirements of those programs; and
Agency staff typically did not know where to start to address the safety issues on their roadways.
Describe the new practice.
A comprehensive approach was developed to assist the local agencies with identifying the safety issues on their roadways, selecting appropriate countermeasures, and applying for funding to make the recommended improvements. The Local Agency Traffic Safety Program was developed to help build a culture of safety throughout the Tampa Bay region and includes:
A yearly Traffic Safety Summit in District 7 for local safety practitioners;
An online HSIP application process;
Safety ambassadors to work one-on-one with the agency staff to develop the candidate HSIP projects; and
Five methods of project delivery assistance by which local agencies can receive Federal safety funding to implement engineering improvements that have been selected for funding including:
Equipment purchase
Technical assistance
Design Build Push Button (DBPB)
Local Agency Program
Local Agency Force Account
List the key accomplishments that resulted from the new practice. Include the roadway safety improvements.
Achieved a 28 percent reduction in fatal and serious injury lane departure crashes and a 33 percent reduction in teen driver crashes over the last three years.
Completed over $23 million in safety improvements on local roadways in the Tampa Bay region.
What technical and/or institutional changes resulted from the new practice?
DBPB project delivery process allows a previously selected designer-contractor team to quickly bring a project “from concept to concrete.”
District 7 Safety Office Traffic Safety Summit.
What benefits were realized as a result of the practice?
Prior to the first Safety Summit, the District Safety Office would typically receive approximately three applications per year for safety funding on local roads. Since the inception of the Safety Summit and the support to the local agencies, the District Safety Office receives over 50 applications annually from the local agencies.
The program embodies the best of what FHWA is trying to achieve through its Every Day Counts initiative—making safety improvements through a multidisciplinary data-driven process as quickly as possible.
Brite Sticks Improve Visibility Day or Night
Mid-block Pedestrian Crossing on Fletcher Avenue Complete Streets Project
From 2004-2007, lane departure crashes accounted for 17.2 percent of all crashes in Michigan, but 47.4 percent of all fatal crashes. Michigan Department of Transportation (MDOT) recognized that while the type and severity of the crashes had similarities, the location at which they occur is random. As a result, MDOT began a three-year statewide initiative in 2008 to install milled centerline rumble strips on all rural non-freeway highways with a posted speed limit of 55 mph, eventually including approximately 5,400 miles of non-freeway roadways. MDOT also installed shoulder rumble strips (SRS) on roadways with paved shoulders of at least 6 feet in width. This systemic initiative is to date the largest of its kind in the United States and provided a unique study opportunity. Consequently, MDOT wished to evaluate the impacts of these rumble strip installations on traffic safety and operation and pavement durability to provide guidance for future implementation both in Michigan and in other states. This evaluation study primarily focused on safety effectiveness of centerline rumble strips (CLRS), since the effectiveness of SRS had previously been established through numerous nationwide research and studies.
What were the key challenges that needed to be addressed before the new practice could be implemented?
MDOT had to ensure that stakeholders were involved in the process and developed and circulated survey to capture the opinions and input of various road users.
Additionally, MDOT developed a pair of rumble strip-based public service announcements for outreach.
The installation of the rumble strips needed to be expedited in order to ensure valid research results.
Describe the new practice.
Centerline rumble strips are a set of transverse grooves applied on the centerline of a roadway to alert inattentive (distracted, drowsy, unfocused, etc.) drivers who may unintentionally drift over the centerline.
Rumble strips provide a tactile and audible warning to alert drivers.
In 2008 MDOT began a three-year statewide CLRS installation initiative, including approximately 5,400 miles of 55 mph, non-freeway roadways over the three-year installation period.
To efficiently roll out the rumble strip installations, the contracting process was streamlined by adding the work items to MDOT's annual pavement marking contracts with the direction to cut the rumble strips ahead of restriping the roadways.
Non-Freeway Shoulder and Centerline Rumble Strip Installation – M-66 in Calhoun County, Michigan
Key accomplishments, including roadway safety improvements.
47 percent reduction in total target crashes (head-on, sideswipe opposite and run-off-the-road left) and a 51 percent reduction in target fatal crashes, as well as reductions in other injuries
Economic analysis resulted in a benefit-cost ratio in the range of 58:1 to 18:1 based on discount rate assumptions of 2 percent and 10 percent, respectively
A road user survey indicated strong agreement among the respondents that CLRS are a beneficial safety improvement program
What technical and/or institutional changes resulted from the new practice?
As a result of the initiative's success, installation of CLRS has become standard practice on trunkline routes in Michigan.
Language in MDOT's Road Design Manual now dictates that CLRS be installed on all 55 mph 2- and 4-lane highways (regardless of whether a section is a passing or non-passing zone) where the lane plus paved shoulder width beyond the rumble strip exceeds 13' in width, with exceptions for high driveway densities and the presence of horse drawn buggies.
What benefits were realized as a result of the practice?
Rumble strips on high-speed non-freeway highways improved driver performance in most traffic scenarios.
CLRS did not contribute to short-term transverse cracking in asphalt pavements.
Approximately 17 percent of all crashes from 2009 through 2011 that have occurred on Arkansas' highways were on wet pavement, resulting in 160 fatalities, or about 53 fatalities per year. One factor is the pavement, or more appropriately, the pavement texture. It can also have an impact on the ability of a vehicle, even with poor condition tires, to maintain contact with the surface, and the ability of the driver to maintain control of his or her vehicle. Of the 160 wet-weather fatalities that occurred from 2009 through 2011, 28 occurred on Arkansas' Interstates, or about 9 fatalities per year.
Arkansas made a previous effort to address roadway departure wet-weather crashes. The State identified several locations on the Interstate system with a high percentage of crashes due to wet pavement. Job 070322, Highway 51-Highway 182 Safety Improvements (S), was awarded in July 2008 and completed in November 2008. The purpose of this project was to overlay approximately four miles of Interstate 30 in Clark County. This project consisted of ultrathin bonded wearing course (UTBWC), cold milling, pavement marking, maintenance of traffic, and other miscellaneous items.
A before-after analysis was conducted within the job limits. In the 48 months prior to the improvement (November 1, 2004 to October 31, 2008), a total of 70 crashes due to wet pavement were observed. In the following 48 months after the project's substantial completion (November 1, 2008 to October 31, 2012), only 5 crashes occurred due to wet pavement. This is a significant reduction of about 93 percent. The benefit-cost ratio for this project is 2.98. Based on a literature review, this is similar to the results experienced in other states.
Describe the new practice.
Based on the previous success of the project on Interstate 30, the Arkansas Highway Commission passed Minute Order 2013-043 in April 2013. This Minute Order authorized the Department to proceed with pavement texture improvement projects to address wet pavement crashes on Arkansas Interstates. Six Interstate locations have been identified for possible UTBWC installation where a reconstruction project is not scheduled for construction within the next four years. Other treatment methods to improve pavement texture may be employed as well. Each of these locations has a high percentage of wet-weather crashes over the last three years.
Arkansas Highway Commission has authorized the Department to proceed with pavement texture improvement projects to address roadway departure wet-weather crashes on Arkansas Interstates.
The general key phases to the implementation of the UTBWC include:
Cold milling,
Pavement marking,
Maintenance of traffic, and
Other miscellaneous items.
List the key accomplishments that resulted from the new practice. Include the roadway safety improvements.
Installation of UTBWC has proven to be an effective low-cost countermeasure to improve skid resistance and reduce hydroplaning potential. In addition to the safety benefits, UTBWC preserves the existing pavement and improves user comfort. Due to the treatment's success, the Arkansas Highway Commission has authorized the Department to proceed with pavement texture improvement projects to address roadway departure wet-weather crashes on Arkansas Interstates. Six other locations with a high percentage of wet-weather crashes between 2009 and 2011 were identified. Addressing these locations with UTBWC will help reduce wet-weather roadway departure crashes, helping the Arkansas Highway State Transit Department fulfill its mission statement and strategic goals, and help Arkansas get one step closer Toward Zero Deaths.
What benefits were realized as a result of the practice?
Significant reduction in wet weather crashes.
UTBWC preserves the existing pavement and improves user comfort.
Further Reading
Brewer,A., & D. Nilles. Improving Interstate Safety with Pavement Surface Treatments. Arkansas Highways Magazine, July, 2013. Pages 10-11.
Oman, N. I-30 job targets rain-tied crashes Accidents drop in resurface test. Arkansas Democrat-Gazette. Front Section. Page 1.
Figure 1. Interstate 30 Westbound (Log mile 58.00) in Clark County
Study Area Crash Map
Figure 2. Study area crash map with before treatment crashes on left and after treatment crashes on right.
The Tennessee DOT (TDOT) Local Roads Safety Initiative (LRSI) was created in 2010 to assist with improving safety on local roads. TDOT created the initiative to assist its counties with road safety improvements. The initiative provides basic signing, striping upgrades, signage for curves, guardrail, and approaches to guard rails. Most counties have limited support staff and very few counties have staff with the needed engineering expertise. Only 6 of 95 county chief administrative officers are licensed engineers. The LRSI was developed by a partnership between the Strategic Highway Safety Plan (SHSP) and safety projects coordinator, State traffic engineer, assistant chief of operations, incident management division director, and the Tennessee FHWA Division. TDOT developed a consultant contract and hired two consultants to conduct local road safety analysis in Tennessee's 95 counties.
Benefit
The TDOT Local Road Safety Initiative has successfully conducted Road Safety Audit Reviews (RSARs) through the draft stage for 45 counties and 21 projects have been let to bid and awarded since the program's inception.
The Ohio DOT's (ODOT) Office of Local Programs, with the assistance of the Ohio Local Technical Assistance Program (LTAP) Center, administers a systemic signage intersection and curve upgrade program for targeted Ohio Townships. The program provides two opportunities for townships to apply for free safety and advanced warning signs.
The Township-wide Systematic Signage Upgrade Program is for Townships with a high number of severe crashes. The Top 50 Townships with a high number of serious crashes for a five-year period are invited to apply for funding to implement systematic signage upgrades.
The Township Corridor Systematic Signage Upgrade Program provides intersection signage and curve upgrades for Townships with a corridor among the Top 50 Township High-Risk Rural Roads in Ohio based on a five-year period of crash data. Townships can apply for funding on designated corridors.
Townships participating in the programs are responsible for installation and maintenance of the signage and are limited to a list of preapproved signs.
As a part of the program, the Ohio LTAP Center provides crash data and information on the types of sign packages available for specific situations. Townships can choose from the signage packages or build their own sign orders. The ODOT Office of Local Programs also provides guidance and assistance to Townships on sign installation if necessary. Program details are available on the ODOT Local Programs web page.
Figure 1. Before and After Photos of Sign Installation Completed as Part of Program.
Source: Ohio Department of Transportation/LTAP
Benefit
The signage packages help insure the townships install the signs according to the requirements of the Ohio Manual of Uniform Traffic Control Devices (OMUTCD).
Original publication: 2013 National Roadway Safety Awards Noteworthy Practices Guide Publication FHWA-SA-14-002; 2013
Description of Practice
Kentucky Transportation Cabinet (KYTC) launched a three-year statewide High Friction Surfacing Treatment (HFST) program at over 75 locations in 2010 to improve pavement friction and reduce roadway departure crashes on horizontal curves. HFST was applied at specific sites where skidding crashes resulted in fatalities, serious injuries, and property damage.
Key Accomplishments and Results
There have been measured reductions in the number of roadway departure crashes on treated surfaces.
Contact
Tracy Allen Lovell, PE
Kentucky Transportation Cabinet, Division of Traffic Operations
502-782-5534 Tracy.Lovell@ky.gov
Original publication: National Roadway Safety Awards: Noteworthy Practices Guide; 2011
Description of Practice
FM 1960 thoroughfare has a daily traffic count of 65,000 vehicles, 50 cross streets, 36 signals, and a driveway density of almost 49 driveways per mile. The crash rate along the corridor had a crash rate 217 percent higher than the statewide average. The Texas Department of Transportation's FM 1960 Median Improvement Project set out to improve mobility and safety along this 8 mile stretch.
Key Accomplishments and Results:
Installation of raised-curb medians, channelized left-turn bays, signal improvements, and striping.
Reduction in conflict points
More efficient traffic operations
Law enforcement officials in the area believe the project will reduce crashes and help emergency vehicles reach their destinations along the corridor more quickly
Modeling indicates a reduction in travel time by 16 percent, delays by 40 percent, and number of stops by 45 percent
