CTRE  en route

Summer 2008

CTRE en route is published twice a year to inform readers about CTRE's projects and programs.

Address: CTRE, 2901 S. Loop Drive, Suite 3100, Ames, IA 50010

Phone: 515-294-8103
FAX: 515-294-0467

Website: www.ctre.iastate.edu/

CTRE Communications:
Marcia Brink
CTRE en route editor:
Michele Regenold

CTRE is an Iowa State University center.

Iowa State University: Becoming the best

Traffic studies in Iowa

Recently, Shauna Hallmark, transportation engineer, has been working on three Iowa traffic safety studies sponsored by the Iowa DOT. Tom McDonald, safety circuit rider, collaborated with her on two projects.

In progress

Rumble stripes

Edge line with freshly cut strips

Milled-in rumble strips soon be painted over with edge line striping resulting in a “rumble stripe.”

Edge line paint can lose its visibility after several months of service. Hallmark and McDonald are evaluating whether edge lines painted over rumble strips, otherwise known as rumble stripes, will improve edge line paint durability and visibility.   

Rumble stripes have been installed on six county road sites as part of a research project that seeks to reduce the incidence and severity of run-off-road crashes. Test sites were chosen based on the Iowa DOT’s list of the top 5 percent of road sections with run-off-road crashes from 2001–2006. Evaluations are taking place on local roads in several Iowa counties. Most test sections are on horizontal curves. Since most county roads do not have paved shoulders, the narrow rumble stripes will be installed along the pavement edge.

Along with the Iowa DOT, the project is sponsored by the Iowa Highway Research Board and FHWA.

Research objectives

“We’re mainly looking for increased visibility of the paint line,” says McDonald. “Increased noise or vibration from the rumble strip is a side benefit.” During the first year after installation, the team will investigate the following:

  • Wet weather visibility of rumble stripes versus traditional edge line painting
  • Long-term durability of the painted edge line
  • Driver travel distance from the edge line before and after installation of rumble stripes

An additional period of at least five years will be necessary to collect and analyze crash data valid for comparison with data collected before the installation of the rumble stripes.


Low-cost traffic calming techniques

The main street through many small rural Iowa communities is a state or county highway with high speeds outside the city limits and a reduced speed section through the rural community. Consequently, drivers passing through the community often enter at high speeds and then maintain those speeds throughout.

When speeds in rural communities are problematic, traffic calming provides a potential solution. Traffic-calming measures are generally used in larger urban areas, and their effectiveness in small communities is unknown.

Hallmark evaluated

  • two gateway treatments in Union and Roland, Iowa, and
  • five single-measure treatments (speed table, on-pavement “SLOW” markings, driver speed feedback sign, tubular markers, and on-pavement entrance treatment) in Gilbert, Slater, and Dexter, Iowa.

Data were analyzed 1, 3, 6, 9, and 12 months after the measures were installed.

Key findings

Overhead view of speed table

Successful speed table in Gilbert, Iowa

  • In Gilbert, a speed table was successful in decreasing speeds both immediately upstream and downstream of the speed table.
  • In Union, the transverse markings appeared to be moderately effective in decreasing vehicle speeds directly downstream of the markings for all three locations, although none of the differences were large. The lane narrowing did not appear to be effective. Once the speed feedback signs were installed, significant speed decreases resulted.
  • In Dexter, a “35 mph,” on-street pavement marking and an 8-in. edgeline were installed. The treatments were effective in reducing speeds at all three of the locations where they were tested. The effectiveness varied over time. Nine months after installation, the effectiveness of the treatments appeared to decrease, most likely due to the fact that the markings had faded over time. The treatments were re-painted, and the effectiveness increased again at the 12-month data collection period.
  • In Roland, the gateway entrance treatments, which consisted of converging chevrons and a “25 mph” on-street pavement marking, were reasonably effective. Speeds decreased at all of the data-collection locations, and decreases remained constant over the year-long data collection period.
  • In Slater, results indicate that the longitudinal channelizers used to form a center island for the southern section of R-38 reduced speeds significantly. The driver speed feedback sign was also found to be effective in reducing speeds. Use of the on-pavement “SLOW” markings did not appear to be effective.

In many cases, even the most effective treatments only reduced mean and 85th percentile speeds by a modest amount. Their true effectiveness is their ability to significantly reduce the number of vehicles traveling over the speed limit.

For more information, visit www.ctre.iastate.edu/research/detail.cfm?projectID=-226410767.

Red-light running camera at top of pole. Man stands nearby.

Front view of a red light running camera

Automatic red light running enforcement

A statewide analysis of red light running (RLR) crashes, using crash data from 2001 to 2006, indicates that an average of 1,682 red light running crashes occur at signalized intersections every year. As a result, red light running poses a significant safety issue for communities.

In Iowa, three communities have used camera enforcement.

Results of the research indicate that RLR cameras were very successful in reducing crashes related to red light running in Davenport and Council Bluffs.

  • In Davenport, a 40 percent reduction in RLR crashes was found.
  • In Council Bluffs, a 90 percent reduction was found. Total crashes also decreased at intersections with RLR camera enforcement.

Reductions in total crashes of 20 percent and 44 percent were found in Davenport and Council Bluffs, respectively.

The reduction in RLR violations was evaluated for Clive. However, a crash analysis could not be conducted since there was less than one year of crash data. The number of RLR violations for intersections with no RLR cameras was compared against RLR violations at camera-enforced intersections. Results of a statistical analysis indicate that on average, RLR violations were 25 times higher in locations without cameras than with cameras.

For more information, visit www.ctre.iastate.edu/research/detail.cfm?projectID=1158685907.