Dynamic Speed Feedback Signs, 2014

Dynamic speed feedback sign (DSFS) systems are traffic control devices that are programmed to provide a message to drivers exceeding a certain speed thresh¬old. A DSFS system typically consists of a speed-measuring device, which may be loop detectors or radar, and a message sign that displays feedback to drivers who exceed a predetermined speed threshold. The feedback may be the driver’s actual speed, a message like “SLOW DOWN,” or activation of a warning device such as beacons or a curve warning sign. For more on this topic by these authors, see also "Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project": http://www.trb.org/main/blurbs/172092.aspx

Improving Safety for Slow Moving Vehicles on Iowa's High-Speed Rural Roadways, TR-572, 2009

Among the variety of road users and vehicle types that travel on U.S. public roadways, slow moving vehicles (SMVs) present unique safety and operations issues. SMVs include vehicles that do not maintain a constant speed of 25 mph, such as large farm equipment, construction vehicles, or horse-drawn buggies. Though the number of crashes involving SMVs is relatively small, SMV crashes tend to be severe. Additionally, SMVs can be encountered regularly on non-Interstate/non-expressway public roadways, but motorists may not be accustomed to these vehicles. This project was designed to improve transportation safety for SMVs on Iowa’s public roadway system. This report includes a literature review that shows various SMV statistics and laws across the United States, a crash study based on three years of Iowa SMV crash data, and recommendations from the SMV community.

Evaluation of Iowa’s 70 mph Speed Limit — 2.5 Year Update, 2009

On July 1, 2005, the State of Iowa implemented a 70 mile per hour (mph) speed limit on most rural Interstates. This document reports on a study of the safety effect of this change. Changes in speeds, traffic volume on and off the rural Interstate system (diversion), and safety (crashes) for on- and off-system roads were studied. After the change, mean and 85th percentile speeds increased by about 2 mph on rural Interstates, but speeding was reduced (the number of drivers exceeding the speed limit by 10 mph decreased from 20 per cent to about 8 per cent). Daytime and nighttime serious crashes were studied for a period of 14 and a half years prior to the change and 2 and a half years afterwards. Simple descriptive statistics reveal increases in all crash severity categories for the 2 and a half year period following the speed limit increase when compared to the most recent comparable 2 and a half year period prior to the increase. When compared to longer term trends, the increases were less pronounced in some severity levels and types, and for a few severity levels the average crash frequencies were observed to decrease. However, fatal and other serious cross-median crashes increased by relatively larger amounts as compared to expected random variation. The study also analyzed crash frequencies grouped into six-month periods, revealing similar findings.

Impact of Left-Turn Phasing on Older and Younger Drivers at High-Speed Signalized Intersections, 2004

Several recent studies have demonstrated differences in safety between different types of left-turn phasing—protected, permitted, and protected/permitted phasing. The issue in question is whether older and younger drivers are more affected by a particular type of left-turn phasing at high-speed signalized intersections and whether they are more likely to contribute to a left-turn related crash under a specific type of left-turn phasing. This study evaluated the impact of different types of left-turn phasing on older and younger drivers at high-speed signalized intersections in Iowa. High-speed signalized intersections were of interest since oncoming speeds and appropriate gaps may be more difficult to judge for older drivers and those with less experience. A total of 101 intersections from various urban locations in Iowa with at least one intersecting roadway with a posted speed limit of 45 mph or higher were evaluated. Left-turn related crashes from 2001 to 2003 were evaluated. Left-turn crash rate and severity for young drivers (14- to 24-year-old), middle-age drivers (25- to 64-year-old), and older drivers (65 years and older) were calculated. Poisson regression was used to analyze left-turn crash rates by age group and type of phasing. Overall, left-turn crash rates indicated that protected phasing is much safer than protected/permitted and permitted phasing. Protected/permitted phasing had the highest left-turn crash rates overall.

Road Safety Audit for US 6 from the ECL of Iowa City to the WCL of West Liberty in Johnson and Muscatine Counties, Iowa, 2008

Approximately 13.2 miles of US 6 in eastern Iowa extends from the east corporate limits of Iowa City, Iowa, to the west corporate limits of West Liberty, Iowa. This segment of US 6 is a service level B primary highway, with an annual daily traffic volume varying from 3,480 vehicles per day (vpd) to 5,700 vpd. According to 2001–2007 crash density data from the Iowa Department of Transportation (Iowa DOT), the corridor is currently listed among the top 5% of non-freeway Iowa DOT roads in several crash categories, including crashes involving excessive speed, impaired drivers, single-vehicle run-off-road, and multiple-vehicle crossed centerline. A road safety audit of this corridor was deemed appropriate by the Iowa Department of Transportation’s Office of Traffic and Safety. Staff and officials from the Iowa DOT, Iowa State Patrol, Governor’s Traffic Safety Bureau, Federal Highway Administration, Center for Transportation Research and Education, and several local law enforcement and transportation agencies met to review crash data and discuss potential safety improvements to this segment of US 6. This report outlines the findings and recommendations of the road safety audit team to address the safety concerns on this US 6 corridor and explains several selected mitigation strategies.

Road Safety Audit for County Road X-37, from the Intersection of G-62 to the East Corporate Limits of Columbus City in Louisa County, Iowa, 2009

A road safety audit was conducted for a 7.75 mile section of County Road X-37 in Louisa County, Iowa. In 2006, the average annual daily traffic on this roadway was found to be 680 vehicles per day. Using crash data from 2001 to 2007, the Iowa Department of Transportation (Iowa DOT) has identified this roadway as being in the highest 5% of local rural roads in Iowa for single-vehicle runoff- road crashes. Considering these safety data, the Louisa County Engineer requested that a road safety audit be conducted to identify areas of safety concerns and recommend low-cost mitigation to address those concerns. Staff and officials from the Iowa DOT, Governor’s Traffic Safety Bureau, Federal Highway Administration, Institute for Transportation, and local law enforcement and transportation agencies met to review crash data and discuss potential safety improvements to this segment of X-37. This report outlines the findings and recommendations of the road safety audit team to address the safety concerns on this X-37 corridor and explain several selected mitigation strategies.

Road Safety Audit for County Road H-46 from Redwood Avenue to the Southerly Corporate Limits of Fairfield in Jefferson County, Iowa, 2010

Jefferson County Road H-46 from Redwood Avenue to the southeast corporate limits (SCL) of Fairfield, Iowa, is a paved roadway approximately 6.5 miles long made of asphaltic concrete pavement with curvilinear alignment. The roadway consists of a 22 ft wide pavement, last overlaid in 2002, with 3 to 4 ft wide earth shoulders. Traffic estimates indicated volumes ranging from 500 to 1,590 vehicles per day, with numbers increasing as the route nears Fairfield. This roadway was found to be among the highest 5 percent of similar Iowa roadways in terms of severity of run-off-road crashes. In response, Iowa Department of Transportation (Iowa DOT) requested a road safety audit to examine the roadway and suggest possible mitigation. Representatives from the Iowa DOT, Federal Highway Administration, Institute for Transportation, local law enforcement, and local government met to review crash data and discuss potential safety improvements to this segment H-46. This report outlines the findings and recommendations of the road safety audit team for addressing the safety concerns on this roadway.

Road Safety Audits for County Road X-23 from IA 2 to the South Corporate Limits of West Point and for County Road W-62 from US 218 to IA 27 in Lee County, Iowa, 2010

On October 20–21, 2009, two road safety audits were conducted in Lee County, Iowa: one for a 6 mile section of County Road X-23 from IA 2 to the south corporate limits of West Point and one for a 9.7 mile section of County Road W-62 from US 218 to IA 27. Both roads have high severe crash histories for the years of 2001 through 2008. Using these crash data, the Iowa Department of Transportation (Iowa DOT) has identified County Road X-23 as being in the top 5 percent of similar roads for run-off-road crashes. The Iowa DOT lists County Road W-62 as a high-risk rural road that has above-average crash numbers and is eligible for funding under the Federal High-Risk Rural Road Program. Considering these issues, the Lee County Engineer and Iowa DOT requested that road safety audits be conducted to address the safety concerns and to suggest possible mitigation strategies.

Road Safety Audit for James Avenue NW and 250th Street NW, from the North Corporate Limits of Tiffin to I-380, in Johnson County, Iowa, 2010

To address safety concerns on James Avenue NW and 250th Street NW, from the North Corporate Limits (NCL) of Tiffin, north and east to I-380 (at North Liberty), the Johnson County engineer requested a road safety audit (RSA). The audit was conducted on September 1, 2010, through a program supported by the Office of Traffic and Safety at the Iowa Department of Transportation (DOT). This road is a seal-coated roadway, about 25-ft wide, but with only about 0-1 ft of earth shoulders. According to 2006 Iowa DOT estimates, traffic volume is about 820 vehicles per day, north from Tiffin to a commercial entrance on 250th Street, then increasing to 2,990 vehicles per day to the on-ramp of Interstate 380 (I-380). Local traffic uses this road as a short-cut to Cedar Rapids, North Liberty, and the I-380/I-80 interchange (to avoid congestion on IA 965). This report outlines the findings and recommendations of the road safety audit team for addressing the safety concerns on this roadway.

Temporary Speed Hump Impact Evaluation, 2002

The main objective of this research was to evaluate the impact of temporary speed humps and speed tables on vehicle speeds, vehicle speed profiles, and traffic volumes along local and/or collector streets in several rural Iowa cities. A 25 mile per hour (mph) temporary speed hump and a 30 mph temporary speed table, both made of recycled rubber, were purchased to test the impact of temporary devices. Two cities volunteered and the speed hump/table was installed on two test streets in the city of Atlantic (Roosevelt Drive and Redwood Drive) and one test street in the city of Le Claire (Canal Shore Drive). The speed hump was installed first and then converted to a speed table. Each device was installed for a period of at least two weeks at the same location. Speed, volume, and resident opinion data were then collected and evaluated.

Evaluation of Work Zone Speed Reduction Measures, 2000

The Iowa Department of Transportation (DOT) has made improving work zone (WZ) safety a high priority. Managing vehicle speeds through work zones is perceived to be an important factor in achieving this goal. A number of speed reduction techniques are currently used by transportation agencies throughout the country to control speeds and reduce speed variation at work zones. The purpose of this project is to study these and other applicable work zone speed reduction strategies. Furthermore, this research explores transportation agencies' policies regarding managing speeds in long-term, short-term, and moving work zones. This report consists of three chapters. The first chapter, a literature review, examines the current speed reduction practices at work zones and provides a review of the relevant literature. The speed control strategies reviewed in this chapter range from posting regulatory and advisory speed limit signs to using the latest radar technologies to reduce speeds at work zones. The second chapter includes a short write-up for each identified speed control technique. The write-up includes a description, the results of any field tests, the benefits and the costs of the technology or technique. To learn more about other state policies regarding work zone speed reduction and management, the Center for Transportation Research and Education conducted a survey. The survey consists of six multipart questions. The third chapter provides summaries of the response to each question.

Assessment of Channelizing Device Effectiveness on High Speed/High Volume Roadways, 2007

Part 6 of the Manual on Uniform Traffic Control Devices (MUTCD) describes several types of channelizing devices that can be used to warn road users and guide them through work zones; these devices include cones, tubular markers, vertical panels, drums, barricades, and temporary raised islands. On higher speed/volume roadways, drums and/or vertical panels have been popular choices in many states, due to their formidable appearance and the enhanced visibility they provide when compared to standard cones. However, due to their larger size, drums also require more effort and storage space to transport, deploy and retrieve. Recent editions of the MUTCD have introduced new devices for channelizing; specifically of interest for this study is a taller (>36 inches) but thinner cone. While this new device does not offer a comparable target value to that of drums, the new devices are significantly larger than standard cones and they offer improved stability as well. In addition, these devices are more easily deployed and stored than drums and they cost less. Further, for applications previously using both drums and tall cones, the use of tall cones only provides the ability for delivery and setup by a single vehicle. An investigation of the effectiveness of the new channelizing devices provides a reference for states to use in selecting appropriate traffic control for high speed, high volume applications, especially for short term or limited duration exposures. This study includes a synthesis of common practices by state DOTs, as well as daytime and nighttime field observations of driver reactions using video detection equipment. The results of this study are promising for the day and night performance of the new tall cones, comparing favorably to the performance of drums when used for channelizing in tapers. The evaluation showed no statistical difference in merge distance and location, shy distance, or operating speed in either daytime or nighttime conditions. The study should provide a valuable resource for state DOTs to utilize in selecting the most effective channelizing device for use on high speed/high volume roadways where timely merging by drivers is critical to safety and mobility.