Safety Evaluation of Wet-Reflective Pavement Markings

Chapter 4. Data Collection

Minnesota, North Carolina, and Wisconsin provided data containing locations and dates of the installation of wet-reflective markings. Reference sites were also identified in each State that were similar to the treated sites in terms of traffic volumes and roadway geometry but had standard lane markings. These States also provided roadway geometry, traffic volumes, crash data, and information on other construction activities for both installation and reference sites. This section summarizes the data assembled for the analysis.

Minnesota

Installation Data

The Minnesota Department of Transportation (MnDOT) provided a list of installations of wet-reflective markings along two-lane roadways and freeways with the year of installation. Data for the installation year were excluded from the analysis. The total length of installations used for this study was 771 mi. The installation information included the route number, milepost, construction period and, where available, whether the markings were used on the center line, edge line, or lane lines. MnDOT applied 3M™ and Epoplex® wet-reflective products.

No other construction activities were reported at these locations.

Reference Sites

Reference sites were identified by selecting two-lane roadways and freeways with characteristics similar to the treated sites. Although no electronic record of pavement marking type was available, MnDOT officials stated that unless the location was in the treatment site data, the markings would not be of a wet-reflective type.

Roadway Data

Roadway data were obtained from the Highway Safety Information Service System* (HSIS) for 2003 to 2012. Roadway data included the following variables:

• Roadway class.
• Area type (urban/rural).
• Shoulder width.
• Shoulder type.
• Median width.
• Number of lanes.

* Revised 3/12/2019

Traffic Data

Traffic data were obtained from HSIS for 2003 to 2012 in the form of average annual daily traffic (AADT).

Crash Data

Crash data were obtained from HSIS for 2003 to 2012, including many variables related to the location, time, and characteristics of each crash.

Treatment Cost Data

MnDOT provided estimated cost information of $8,500/mi for ground-in markings and $1,900/mi for striping. These costs are per center line mile and would be doubled to $17,000 and $3,800/mi, respectively, for the four-lane freeway locations.

MnDOT uses a recommended service life of 2 years for pavement markings.

North Carolina

Installation Data

The North Carolina Department of Transportation (NCDOT) provided a list of projects that placed wet-reflective markings on the edge line and/or lane lines on urban and rural freeways. The total length of roadway installations used in this study was 95 mi. Among the data provided by the reports were the location (including district, State route number, and mileposts) and the construction dates. Data for the installation year were excluded from the analysis. The records also indicated whether the wet-reflective markings were applied as a restriping project or as part of a resurfacing project.

The following three products were applied:

• Glomarc® 90 manufactured by Epoplex®.
• LS90™ manufactured by Epoplex®.
• Liquid Pavement Marking Series 1200 manufactured by 3M™.

No other construction activities were reported at these locations.

Reference Sites

NCDOT also provided a list of locations that received standard pavement markings, which was used to identify reference sites. The list was further reduced by including only those sites whose roadway class was indicated as being urban or rural freeway.

Roadway Data

Roadway inventory data were obtained from the HSIS for 1998 to 2012. Roadway data included the following variables:

• Area type (urban/rural).
• Functional class.
• Divided versus undivided.
• Median width.
• Terrain.
• Number of lanes.
• Surface width.
• Shoulder type.
• Shoulder width.
• Surface type.
• Speed limit.

Traffic Data

Traffic data were obtained from HSIS for 1998 to 2012 in the form of AADT and percentage of trucks.

Crash Data

Crash data were obtained from HSIS for 1998 to 2012, including many variables related to the location, time, and characteristics of each crash.

Treatment Cost Data

NCDOT provided approximate installation costs of $1.10 and $2.25 per linear ft for polyurea and tape, respectively. The equation in figure 6 is the basis for calculating the cost:

Figure 6. Equation. Calculation for treatment costs in North Carolina.

This cost includes marking the four edge lines with a constant application and the skip lines, which cover a quarter of the pavement in marking material. A 4-lane road will have 2 skip lines, a 6-lane road will have 4 skip lines, an 8-lane road will have 6 skip lines, and a 10-lane road will have 8 skip lines.

Service life estimates provided by NCDOT are less than 5 years for tape and 8 years for sprayed polyurea with high initial retroreflectivity values.

Wisconsin

Installation Data

The Wisconsin Department of Transportation (WisDOT) provided a list of projects in which wet-reflective markings were placed on urban and rural freeways and multilane divided roadways. The total length of roadway installations used in this study was 300 mi. Among the data provided by the reports were the location (linkable to the WisDOT Metamanager data system) and the construction dates. Data for the installation year were excluded from the analysis.

WisDOT applied the following two wet-reflective marking products:

• 380WR marking tape manufactured by 3M™.
• A380AW marking tape manufactured by 3M™.

These markings were installed on the lane lines only. Approximately 50 of the 300 mi used for analysis had shoulder widening and/or shoulder rumble strips installed at the same time. These locations were mostly on freeways. No further construction was reported on these road segments by WisDOT during the study period.

Reference Sites

Reference sites were identified by using those locations that received the wet-reflective markings after the treatment sites used in this study. The sum of reference site mi was 341 mi.

Roadway Data

Roadway inventory data were obtained from the Metamanager system maintained by WisDOT for 2003 to 2012. The data are bidirectional, meaning that unlike the data for Minnesota and North Carolina, each record was for only one direction of travel. Roadway data included the following variables:

• Area type (urban/rural).
• Functional class.
• Divided versus undivided.
• Median width.
• Median type.
• Number of lanes.
• Traveled way width.
• Shoulder type.
• Shoulder width.
• Paved shoulder width.
• Presence of rumble strip.

Traffic Data

The project team obtained traffic data in the form of AADT from WisDOT for 2012 and a projected AADT for 10 years out. WisDOT recommended extrapolating the AADTs for previous years. The percentage of trucks in the traffic stream was also provided.

Crash Data

WisDOT provided crash data for 2003 to 2012 for all treatment and reference sites. The compiled crash data contained many variables related to the location, time, and characteristics of each crash.

Treatment Cost Data

The following costs were provided by WisDOT based on average bid prices on 2012, 2013, and 2014 projects:

• Inlaid into asphalt 4-inch tape—$5,800/mi for single lane line mi.
• Inlaid into asphalt 8-inch tape, placed mainly at ramp gores/channelizing lines—$5,800 per gore.
• Grooved white 4-inch tape—$5,800/mile for single lane line.
• Grooved white 8-inch tape –$5,000 per ramp gore.
• Grooved contrast 4-inch tape—$9,200/mi for single lane line mile.
• Grooved contrast 8-inch tape—$7,300 per gore ramp.

A service life of 8 years was assumed for the grooved treatment. The tape product has only been available for a few years, so the wet reflectivity service life and durability is still unknown.

Data Characteristics and Summary

Table 1 defines the crash types used by each State. An attempt was made to make the crash type definitions consistent. In all States, intersection-related, animal-related, and snow/slush/ice-related crashes were excluded because these crash types were not correctable by the treatment under study.

Table 2 provides summary information for the data collected for the treatment sites. The information in table 2 should not be used to make simple before–after comparisons of crashes per mi-year because such comparisons would not account for factors, other than the strategy, that may cause a change in safety between the before and after periods. Such comparisons are properly done with the EB analysis as presented later in this report.

Table 3 provides summary information for the reference site data. Comparisons of crash rates between States and between treatment and reference sites should consider that the rates were only per mile and traffic volumes were not considered.

Table 1. Definitions of crash types by State.

Table 2. Data summary for treatment sites.

Table 3. Data summary for reference sites.