Safety Evaluation of Edge-Line Rumble Stripes on Rural Two-Lane Horizontal Curves

Chapter 5. Data Collection

Kentucky and Ohio provided data containing locations and dates of the installation of ELRSs. These States also provided roadway geometry, traffic volumes, and crash data for both installation and reference sites. This chapter summarizes the data assembled for the analysis. Additional details about the design, installation, and maintenance of ELRSs, as well as lessons learned, can be found in the appendix of this report.

Kentucky

This section describes the installation data, reference sites, roadway data, traffic data, crash data, and treatment cost data for Kentucky sites used in this evaluation.

Installation Data

The Kentucky Transportation Cabinet (KYTC) provided a list of roadway sections where ELRSs were installed as part of resurfacing projects. The treatment consisted of adding the new pavement surface, installing milled rumble strips, and painting the edge line on top of the strip. KYTC resurfaced shoulders along with the travel lanes but did not widen shoulders as part of this effort. KYTC installed the milled rumble strips with a standard 12-inch width and 1‑inch depth. Installations took place on corridors consisting of both tangents and horizontal curves. Kentucky staff identified specific curves for treatment sites for this study using the geographic information system (GIS) roadway curve inventory to select moderately to very sharp curves (i.e., Highway Performance Monitoring System (HPMS) classes D, E, and F) within these treated corridors. The final list of treated sites comprised 229 horizontal curves (15.6 mi) where KYTC installed ELRSs.

Reference Sites

The treatment applied by KYTC had the potential for crash migration or spillover effects. Crash migration occurs when there is “a transfer of crashes resulting from an improvement rather than a reduction” (p. 4).⁽³⁷⁾ Spillover occurs when the safety benefits of a treatment extend to untreated sites downstream of the treated site.

To detect crash migration and spillover effects, the project team used a two-stage approach involving two reference groups. In the first stage, the project team selected one reference group from a large sample of untreated sites less than 5 mi downstream of treated sites and a second group from a limited sample of untreated sites located greater than 5 mi downstream of treated sites. Two reference groups were selected in this way to observe potential crash migration or spillover effects in the first reference group. According to a simulator study involving drowsy drivers and rumble strips, signs of drowsiness return to drivers approximately 5 min after hitting a rumble strip.⁽³⁸⁾ Assuming a 5-min drowsiness-relapse time and vehicle speed equal to or less than 60 mi/h, the project team observed crash migration and spillover effects within 5 mi of a treated site. By comparing the crash data of these two reference groups, the existence and magnitude of the crash migration and spillover could be detected. If no crash migration or spillover effects were detected, then the two reference groups were pooled together to form the reference group for the EB method.

Roadway Data

Roadway data provided by Kentucky staff were in GIS shapefile format. The various road characteristics (e.g., shoulder width) were contained in separate shapefiles, each segmented differently. GIS files were obtained from the Kentucky Roadway Information and Data website. The most useful file segmented the Kentucky road network into curve and tangent sections, likely for HPMS purposes. Each curve was denoted along with its degree of curvature and HPMS curve classification (A–F). Spatial joining was used to glean the available roadway characteristic information: shoulder type and width, traffic volume, and degree of curvature. To obtain many other roadway characteristics, such as area type, number of lanes, illumination, rumble strip presence, and roadside hazard rating, the data collectors used Google® Maps™ and Google® Street View™ imagery. To locate and view the curve in Google® Maps™, the coordinates of the curve were extracted from the GIS map, imported to Microsoft® Excel, and concatenated into a hyperlink that could be used to quickly find that location in Google® Maps™.

Traffic Data

KYTC maintains traffic volume data in the GIS inventory files, specifically the Traffic Flow (TF) shapefile. The project team obtained traffic data for the treatment and reference sites by spatially joining the TF layer to the site layer to obtain the current and past years’ AADT values.

Crash Data

Crash data for Kentucky are publicly available on the Kentucky State Police’s crash data website.⁽³⁹⁾ The project team used the following specifications for crash queries for each route:

• Crash query dates were from 1/1/2004 to 12/31/2012.
• A crash study area was defined for each horizontal curve, which consisted of up to 0.05 mi on each approach of the horizontal curve. If two curves were closer than 0.10 mi, then the study area was defined as the midpoint between the curves.
• Separate files for collisions, units, and individuals were obtained for each site.

Treatment Cost Data

KYTC provided estimates of the costs and service lives of the treatments for use in conducting a B/C analysis of the treatment (table 11).

Ohio

This section describes the installation data, reference sites, roadway data, traffic data, crash data, and treatment cost data for Ohio sites used in this evaluation.

Installation Data

The Ohio Department of Transportation (ODOT) provided a list of roadway sections where ELRSs were installed on nonfreeway highways. The Highway Safety Information System (HSIS) provided data identifying rural two-lane segments, and extents of horizontal curves. The project team verified installations using ODOT’s video logs as well as Google® Streetview^TM. Most installations were confirmed but several treatment sites were noted to have not received the ELRS installation. The final list of treated sites comprised 579 horizontal curves (42.3 mi) where ELRSs were installed.

Reference Sites

As with the Kentucky data, the project team used two reference groups in Ohio to account for spillover or crash migration effects. The project team selected both reference groups (within 5 mi of treatment sites and more than 5 mi downstream of treated sites) from the list of installation sites that were not actually treated and were upstream/downstream of installation sites on the same corridors. The final list of reference sites comprised 428 horizontal curves (26.1 mi).

Roadway Data

Roadway data were obtained from the HSIS for each study year. Requisite roadway data for identifying study sites included functional classification, number of lanes, and extents of horizontal curvature. Additional data included degree of curvature, posted speed limit, and shoulder width. The project team used route, beginning milepost, and ending milepost to merge roadway data with traffic data and crash data.

Traffic Data

The project team obtained traffic data from the HSIS for each study year. Traffic data were obtained for the treatment and reference sites to obtain current and past years’ AADT values. While data have not been collected every year, HSIS data included AADT information for each year in the study.

Crash Data

The project team obtained Ohio crash data from the HSIS for each study year. The project team used the following specifications for crash queries for each route:

• Crash query dates were from 1/1/2005 to 12/31/2013.
• A crash study area was defined for each horizontal curve, which consisted of up to 0.05 mi on each approach of the horizontal curve. If two curves were closer than 0.10 mi, then the study area was defined as the midpoint between the curves.

Treatment Cost Data

ODOT provided estimates of the costs and service lives of the treatment for use in conducting a B/C analysis of the treatment (table 12).

Data Characteristics and Summary

Table 13 defines the crash types used by each State. The project team attempted to make the crash type definitions consistent. In all States, intersection-related and animal-related crashes were excluded.

Table 14 provides summary information for the data collected for the treatment sites. The information in table 14 should not be used to make simple before–after comparisons of crashes per mile-year because it does not account for factors (other than the strategy) that might cause a change in safety between the before and after periods. Such comparisons were properly done with the EB analysis, as presented later. Table 15 and table 16 provide summary information for the reference site data for Kentucky and Ohio, respectively. As discussed previously, separate reference groups were established to identify potential spillover and crash migration effects.