Neal Hawkins

Pavement Marking Retroreflectivity: Analysis of Safety Effectiveness

Previous research has shown that greater longitudinal pavement marking retroreflectivity levels increase drivers’ visibility and detection distance. However, increased visibility may cause drivers to feel too comfortable during nighttime conditions, and drivers may then pay less attention, operate their vehicles at unsafe speeds, or both. Before-and-after studies have been conducted on a pavement marking improvement such as repainting stripes or changing to a more durable marking material. Studies have also used models to estimate the retroreflectivity on the basis of the date of installation and vehicle exposure or have assumed a linear reduction in retroreflectivity over time. Only two studies have related field-measured pavement marking retroreflectivity to safety performance (crash data). One study analyzed the relationship between 3 years of pavement marking retroreflectivity data collected by the Iowa Department of Transportation on all state primary roads and corresponding crash and traffic data. The other study developed a spatial–temporal database by using measured retroreflectivity data to account for the deterioration of pavement markings over time, along with a statewide crash database to attempt to quantify a relationship between crashes and the quality (measured by retroreflectivity) of pavement marking. Three sets of data were analyzed: the complete database, records for two-lane roads, and records with retroreflectivity values less than or equal to 200 mcd/m2/lx only. The distributions and models of the entire database and the two-lane records did not show that poor pavement marking retroreflectivity correlated to a higher crash probability. However, when only records with retroreflectivity values of 200 mcd/m2/lx or less were examined, a statistically significant, albeit weak, relationship was determined.

An empirical analysis of farm vehicle crash injury severities on Iowa's public road system

Farm vehicle crashes are a major safety concern for farmers as well as all other users of the public road system in agricultural states. Using data on farm vehicle crashes that occurred on Iowas public roads between 2004 and 2006, we estimate a multinomial logit model to identify crash-, farm vehicle-, and driver-specific factors that determine farm vehicle crash injury severity outcomes. Estimation findings indicate that there are crash patterns (rear-end manner of collision; single-vehicle crash; farm vehicle crossed the centerline or median) and conditions (obstructed vision and crash in rural area; dry road, dark lighting, speed limit 55 mph or higher, and harvesting season), as well as farm vehicle and driver-contributing characteristics (old farm vehicle, young farm vehicle driver), where targeted intervention can help reduce the severity of crash outcomes. Determining these contributing factors and their effect is the first step to identifying countermeasures and safety strategies in a bid to improve transportation safety for all users on the public road system in Iowa as well as other agricultural states.

Use of Physical Devices for Calming Traffic Along Major Roads Through Small Rural Communities in Iowa

Many rural communities have developed around highways or major county roads. As a result, the main street through small rural communities is often part of a high-speed rural highway. Highways and county roads are characterized by high speeds outside the city limits and then transition into a reduced-speed section through the rural community. Consequently, drivers passing through the community may enter at high speeds and then maintain those speeds throughout. Traffic calming in small rural communities along major roadways is common in Europe, but the United States does not have experience with applying traffic calming outside of major urban areas. Seven different low-cost traffic treatments were implemented and evaluated in five rural Iowa communities. Two of the treatments physically affected the roadway cross-section. A speed table was placed along the major road (County Highway E-23) in Gilbert, Iowa, and longitudinal channelizers were used to create a center island narrowing along County Highway R-38 in Slater, Iowa. Before and after speed studies were conducted. Speed studies were conducted at 1, 3, 9, and 12 months after installation of the treatments to evaluate their effectiveness over time. Both treatments successfully reduced mean speed, 85th percentile speed, and fraction of vehicles traveling 5, 10, 15, and 20 mph over the posted speed limit; reductions were sustained over time.

Reliability of Probe Speed Data for Detecting Congestion Trends

This paper presents a framework for evaluating the reliability of probe-sourced traffic speed data for congestion detection and general infrastructure performance assessment. The methodology outlined employs pattern recognition and time-series analysis to accurately quantify the similarity and dissimilarities between probe-sourced and benchmarked local sensor data. First, an adaptive and multiscale pattern recognition algorithm called Empirical Mode Decomposition (EMD) is used to define short, medium and long-term trends for the probe-sourced and infrastructure mounted local sensor datasets. The reliability of the probe data is then estimated based on the similarity or synchrony between corresponding trends. The synchrony between long-term trends are used as a measure of accuracy for general performance assessment, whereas short and medium term trends are used for testing the accuracy of congestion detection with probe-sourced data. Using one-month of high-resolution speed data, the authors were able to use probe data to detect on average 74% and 63% of the short-term events (events lasting for at most 30 minutes), 95% and 68% of the medium-term events (events lasting between 1 and 3 hours) on freeways and non - freeways respectively. Significant latencies do however exist between both datasets. On non - freeways, the benchmarked data detected events, on average, 12 minutes earlier than the probe data. On freeways, the latency between the datasets was reduced to 8 minutes. The resulting framework can serve as a guide for state DOTs when outsourcing or supplementing traffic data collection to probe-based services.

Measurement and Analysis of Heterogenous Vehicle Following Behavior on Urban Freeways: Time Headways and Standstill Distances

Microscopic traffic modelling is a popular tool in the transportation field, but using such models comes with significant data needs in order to properly calibrate them. Two important driver behavior parameters in these models are the preferred time headways and standstill distances. In this paper, an economical method for collecting headways and standstill distances is presented and applied to urban freeways in Iowa, USA. The following time headways and standstill distances were categorized into four combinations of car and truck pairs. It was found that headway values largely depend on the following vehicle type-when a car was following the average headway was around 2 seconds, compared to around 3 seconds when a truck was following. Additionally, the car-car combination leaves much less space when stopped than when a pair involves trucks. In particular, the average standstill distance of a car following a car was found to be around 9 feet, while the average standstill distances are around 12 feet when a truck is involved. However, both headways and standstill distances follow fairly disperse distributions, due to the heterogeneity in driver behavior. Thus, microsimulation software should be improved to allow these parameters to follow distributions.

Integrated Approach to Pavement Marking Management

Providing good pavement marking performance is an essential component of the transportation system. According to Tom Welch, state safety engineer for the Iowa Department of Transportation (DOT), “Every older driver forum has included a consistent demand for brighter and more durable pavement markings.” This paper summarizes some management tools developed for Iowa DOT as part of a pavement marking management system (PMMS). A summary of how retroreflectivity data are used statewide in managing pavement marking performance is provided as well as a discussion of how the PMMS was integrated with other infrastructure management resources for Iowa DOT.

Speed reduction impact of dynamic speed feedback signs on high crash curves

Lane departure crashes are a significant safety concern. The majority of lane departure crashes occur in rural areas, mostly on 2-lane roadways. A disproportionate number of these crashes occur on horizontal curves. Curve related crashes involve a number of roadway and driver causative factors. A primary driver factor is speeding and a large number of run-off-road fatal crashes on curves are speed related. The amount of speed change needed from the tangent speed to the speed required to traverse a curve has an impact on the frequency and severity of crashes on curves.

Framework for Evaluating the Reliability of Wide-Area Probe Data

This paper presents a framework for evaluating the reliability of probe-sourced traffic speed data for detection of congestion and assessment of roadway performance. The methodology outlined uses pattern recognition to quantify accurately the similarities and dissimilarities of probe-sourced and benchmarked local sensor data. First, a pattern recognition algorithm called empirical mode decomposition was used to define short-, medium-, and long-term trends for the probe-sourced and infrastructure-mounted local sensor data sets. The reliability of the probe data was then estimated on the basis of the similarity or synchrony between corresponding trends. The synchrony between long-term trends was used as a measure of accuracy for general performance assessment, whereas short- and medium-term trends were used for testing the accuracy of congestion detection with probe-sourced data. By using 1 month of high-resolution speed data, the authors were able to use probe data to detect, on average, 74% and 63% of the short-term events (events lasting for at most 30 min) and 95% and 68% of the medium-term events (events lasting between 1 and 3 h) on freeways and nonfreeways, respectively. Significant latencies do, however, exist between the data sets. On nonfreeways, the benchmarked data detected events, on average, 12 min earlier than the probe data. On freeways, the latency between the data sets was reduced to 8 min. The resulting framework can serve as a guide for state departments of transportation when they outsource collection of traffic data to probe-based services or supplement their data with data from such services.

Practice of Rumble Strips and Rumble Stripes

This synthesis documents current practices used by states installing rumble strips and explores variations in practice in terms of design, criteria, and locations for installation, maintenance, perceived benefits, communication of benefits, and important issues. Information was acquired through a literature review, survey on current practice, and case examples. The survey also included questions specific to the state of practice for rumble stripes, which is the term used when the pavement marking lines are painted on the rumble strip in an effort to increase visibility during inclement weather conditions. The findings indicate that two-thirds of the state agencies rely on traditional methods to address the noise issue: skipping rumbles in residential areas, adjusting their depth, or not installing rumbles at all. The overwhelming majority of responding states, 83%, have developed policies or guidance to modify their rumble design practices to be sensitive to cyclists. Fewer than half the respondents have developed policies/guidance to address pavement deterioration; several agencies indicated that pavement condition is a factor on whether to install a rumble or not. The survey also showed that very few state DOTs have created public campaigns to explain that the use of rumbles improves safety so that complaints regarding noise, bicycle issues, and other are minimized.

Use of DSFS as a Speed Transition Zone Countermeasure in Small, Rural Communities

Small rural communities in the United States are often located along major state or county roadways and as a result, most of the traffic along their main thoroughfare is pass-through rather than local traffic. Unfortunately, drivers passing through these communities often enter at high rates of speeds which are sometimes significantly higher than the posted speed of the local segment. High speeds create a safety issue for rural communities. They also discourage pedestrian activities, such as walking and bicycling, and discourage community interaction and vitality. Rural communities often lack engineering staff and resources to address speed management. As a result, rural communities find it difficult to address speeds and in many cases, utilize stop signs and lower speed limits to address the problem which may lead to disregard for traffic control. Traffic calming in rural areas requires different considerations than urban areas and within the US, rural traffic calming is in its infancy with little experience or guidance for agencies to draw on. This paper summarizes the results of a study which evaluated several different types of dynamic speed feedback signs which were deployed within the speed transition zone for small rural communities in Iowa (USA). DSFS have been used in a number of applications in the US, such as within school zones and work zones. Their effectiveness was less known in rural community applications. Three different types of DSFS were deployed (simple speed feedback sign, alphanumeric sign, and speed limit sign with LED array). All signs were programmed to activate only for drivers traveling at some threshold over the posted speed limit at the community entrance. Overall, the dynamic speed feedback signs were shown to be very effective in reducing vehicle speeds at community entrance. In particular, large reductions were noted in most cases in the fraction of vehicles that were traveling significantly over the posted speed limit at the community entrance.