Projects
The Effectiveness of Overhead Mounted Regulatory Speed Signs on Operating Speed
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Project Status: |
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Description:
The objective of this research was to evaluate
the effectiveness of overhead mounted regulatory speed signs as a
speeding countermeasure (i.e., reducing average operating speed). It was
hypothesized that a regulatory speed sign placed overhead and in the
driver’s line of sight will be effective in gaining speed limit
compliance.
Rationale:
Speed data from the Milwaukee freeway system shows
many drivers “driving too fast” and exceeding the posted speed limit.
Average speeds on the freeway system continue to increase. Although
enforcement is an effective countermeasure to speeding, there are simply
not enough law enforcement personnel to adequately enforce speed
throughout the freeway system. There is a need to identify one or more
non-enforcement countermeasures that are effective in reducing speed on
the freeways and highways of Wisconsin.
Overview:
Speeding continues to be a significant safety problem on our nations
roadways. At operating speeds higher than posted speed limits, a
driver’s ability to safely control, guide, and navigate a vehicle is
significantly reduced. The National Highway Traffic Safety
Administration (NHTSA) defines speeding, in terms of speed-related crash
statistics, as driving too fast for conditions or exceeding the posted
speed limit as a contributing factor in a crash. In 2003, speeding was a
contributing factor in 31 percent of all fatal crashes leading to 13,380
fatalities. NHTSA estimates the economic cost to society of
speeding-related crashes to be $40.4 billion per year, or $1,281 each
second of every day.
Wisconsin is no exception to the national statistics. In 2003, speed was listed as a contributing cause in 16 percent of all crashes and 34 percent of fatal crashes. Speed data from the Milwaukee freeway system shows many drivers “driving too fast” and exceeding the posted speed limit. Average speeds on the freeway system continue to increase. Although enforcement is an effective countermeasure to speeding, there are simply not enough law enforcement personnel to adequately enforce speed throughout the freeway system. There is a need to identify one or more non-enforcement countermeasures that are effective in reducing speed on the freeways and highways of Wisconsin.
The objective of this research was to evaluate the effectiveness of overhead mounted regulatory speed signs as a speeding countermeasure (i.e., reducing average operating speed). It was hypothesized that a regulatory speed sign placed overhead and in the driver’s line of sight will be effective in gaining speed limit compliance. Speed limit signs were placed at overhead locations (on bridges) at three different locations along the Milwaukee freeway system. The study site selected included IH 94 WB @ Rawson Avenue, IH 94 EB @ Sunnyslope Road, and IH 43 SB @ Good Hope Road. Speed data was collected using two different methodologies. First, speed data were obtained from the automated data collection detector locations using the Wisconsin Department of Transportation (WisDOT) Traffic Operations Center (TOC) Data Extractor software. Second, a spot speed (~100 Lidar speed samples) data collection effort was conducted by Traffic Operations and Safety (TOPS) Laboratory staff. To assure that any identified changes in speed, after the speed sign installations, were not the result of random fluctuations in the system, several control sites were included. Control sites were sites with similar characteristics to the study sites but with no treatments applied (i.e., no speed sign installations) or other relevant changes during the study period.
Each speed sign was installed on July 26, 2004. Before speed data was obtained from July 5 to July 23, 2004. After data was obtained from July 27 to August 18, 2004. Data was obtained immediately after the speed sign was installed to allow the research team to evaluate both the potential immediate ‘novelty’ impact of the speed signs as well as the long-term affect over a three-week period. Between 75 and 100 individual vehicle speeds were typically evaluated within each 5-minute speed bin. Given the large number of speed bins considered over the before and after study period, over 8 million speed observations were included in the analysis.
The results of one study site, IH 94 WB @ Rawsom Avenue, is presented in the table below. As can be observed, there was little change in operating speeds after the installation of the speed limit signs. Overall, there is no significant evidence to suggest that the installation of 55 mph regulatory speed signs on bridge overpasses had any impact on average operating speed at any study site. Results from each study site showed very little change in average operating speeds after the speed sign was installed. Average operating speeds in the after time period varied above and below the average operating speed in the before condition which can be attributed to random fluctuations in the operating conditions. The same variability was found at the control sites supporting this claim. Evaluation of the data extractor speed data by comparison to speed data obtained with a lidar indicated no significant differences.
An additional evaluation was conducted to see if the speed signs had a short-term ‘novelty’ effect on average speed, meaning a reduction in averages speeds immediately after installation. The results showed no difference in average operating speeds immediately before and after the signs were installed.
Documents:
| Document Name | Files | Date Posted |
|---|---|---|
| The Effectiveness of Overhead Mounted Regulatory Speed Signs on Operating Speed - Summary Report - November 1, 2004 | Speed Sign Project - Summary Report (PDF, 947KB) |
11/23/2004 |