Institute for Transportation

About the research

Several work-zone traffic control devices have not yet been evaluated to the American Association of State Highway and Transportation Officials’ (AASHTO’s) Manual for Assessing Safety Hardware, Second Edition (MASH 2016) safety performance criteria. Devices commonly used by Smart Work Zone Deployment Initiative state sponsors were summarized. A non-proprietary Type III barricade was selected for testing, as no non-proprietary barricades had been evaluated to MASH 2016. The Type III barricade had 8-ft (2.4-m) long plastic barricade panels, a 30-in. x 48-in. (762-mm x 1,219-mm) aluminum sign attached to the top two plastic barricade panels. The 2-in. (51-mm) square legs and 1¾-in. (44-mm) square uprights were 14-gauge perforated square steel tube. The barricade also had two warning lights attached at the top of each upright. The Type III barricade was tested to MASH 2016 test designation no. 3-71 with a 2,426-lb (1,100-kg) small car. One barricade was impacted at a speed of 64.7 mph (104.1 km/h) and at an impact angle of 90 degrees, and the other barricade was impacted at a speed of 61.2 mph (98.5 km/h) and an impact angle of 0 degrees. Both tests successfully met all evaluation criteria in MASH 2016 for test designation no. 3-71.

About the research

The main objective of this synthesis was to identify and summarize how agencies collect, analyze, and report different work-zone traffic-performance measures, which include exposure, mobility, and safety measures. The researchers also examined communicating performance to the public. This toolbox provides knowledge to help state departments of transportation (DOTs), as well as counties and cities, to better address reporting of work-zone performance.

About the research

Increasing travel demands and an aging highway infrastructure drive the need for extensive construction, maintenance, and utility work zones. The introduction of work zone environments creates risks for both drivers and construction workers due to changes from the normal driving environment. Temporary speed limit reductions are a common countermeasure aimed at improving work zone safety. In theory, reduced speed limits may serve at least three important functions: reduce variability in travel speeds and the potential for work zone crashes, reduce average travel speeds and the severity of crashes when they do occur, and enhance worker safety. Thus, understanding how reducing work zone speed limits impacts travel speeds is an important task.

This project evaluates the impacts of speed limit reductions on drivers’ speed selection at both aggregate and disaggregate levels. Data were collected from nine construction work zones in Iowa during 2014 and 2015. The lack of availability of data pertaining to the location, time, and type of activity significantly constrained the level of analysis that could be conducted for this research. Therefore, the crash analysis was not deemed reliable due to the inconsistency among the multiple data sets that were used to determine the location, time, and type of work zone activity. For the speed analysis, a quantile regression model was employed to examine the impacts of speed limit reductions on speed distribution quantiles before and during construction activities. The results show that speeds are consistently reduced when work zone speed limits are in place.

About the research

In work-zone configurations where lane drops are present, merging of traffic at the taper presents an operational concern. In addition, as flow through the work zone is reduced, the relative traffic safety of the work zone is also reduced. Improving work-zone flow-through merge points depends on the behavior of individual drivers. By better understanding driver behavior, traffic control plans, work zone policies, and countermeasures can be better targeted to reinforce desirable lane closure merging behavior, leading to both improved safety and work-zone capacity.

The researchers collected data for two work-zone scenarios that included lane drops: one on the Interstate and the other on an urban roadway. Then, these scenarios were modeled and calibrated in Vissim using real-world speeds, travel times, queue lengths, and merging behaviors (percentage of vehicles merging upstream and near the merge point).

Once built and calibrated, strategies for the various countermeasures were modeled in the work zones. The models were then used to test and evaluate how various merging strategies affect safety and operations at the merge areas in these work zones.

About the research

What effect does work activity have on traffic conditions in a work zone? This question has still not been answered satisfactorily in practice. Without knowing the true effect a work activity has on traffic, practitioners are forced to make assumptions while scheduling work. This report attempts to answer this question by studying the traffic flow characteristics for various work activities, i.e., traffic speed versus flow curves, capacity reduction factors, and free-flow speed reduction factors.

The importance of the speed-flow curves and reduction factors for work zone planning is also stressed in the latest edition of the Highway Capacity Manual (HCM). The HCM recommends capacity and speed reduction factors for work zones yet does not include specific guidance for including the impact of work activities.

Three traffic stream models, Gipps, Newell-Franklin, and Van Aerde, were calibrated using field data from St. Louis, Missouri.

The Van Aerde model offered the best fit with the field data compared to the other two models. Using the Van Aerde model-generated speed-flow curves, it was found that the capacity for bridge-related activities varied from 1,416 vehicles per hour per lane (vphpl) to 1,656 vphpl and for pavement-related activities from 1,120 vphpl to 1,728 vphpl.

The capacity reduction factor for different work activities was found to be in the range of 0.68 to 0.95, while the free-flow speed reduction factor was found to be in the range of 0.78 to 1.0. The methodology proposed in this report allows the incorporation of work activity effects into traffic impact assessment tools and results in quantitative guidance for work zone planning and design.

Funding Sources:
Midwest Transportation Center
Smart Work Zone Deployment Initiative ($57,942.00)
USDOT/OST-R ($50,185.00)
Total: $108,127.00

Contract Number: DTRT13-G-UTC37

About the research

Road maintenance activities involve both short-term stationary work zones and moving work zones. Moving work zones typically involve striping, sweeping, pothole filling, shoulder repairs, and other quick maintenance activities. Existing traffic analysis tools for work zone scheduling are not designed to model moving work zones.

A review of existing literature showed that many of the existing studies of moving bottlenecks are theoretical in nature, limited to certain lane configurations, and restrictive in the types of mobile work zone attributes considered. This research project sought to address this gap in existing knowledge by using field data from moving work zones to develop and calibrate a traffic impact analysis tool.

This objective was accomplished through the fusion of multiple sources of work zone and traffic data. Four different data sources were used: Missouri Department of Transportation (MoDOT) electronic alerts (e-alerts), probe-based travel times, data from point detectors, and field videos of moving work zones recorded from the back of a truck-mounted attenuator (TMA).

A linear regression model was developed to predict traffic speed inside a moving work zone. Predictor variables in the models included historical speed, number of lanes, type of lane closure, and time of day. The simulation tool VISSIM was calibrated for moving work zones using information extracted from videos of moving work zone operations. The three recommended calibration parameters are a safety reduction factor of 0.7, a minimum look ahead distance of 500 ft, and the use of a smooth closeup option. These calibration values can be used by departments of transportation (DOTs) to model moving work zone scenarios.

The operational analysis concluded that a moving work activity lasting one hour or more operates best when traffic volumes are under 1,400 veh/hr/ln, and preferably under 1,000 veh/hr/ln. Further, scheduling shorter duration moving activities on high-volume roads at multiple times (on the same day or on different days) works better than scheduling a longer duration activity. The safety analysis generated tradeoff plots between the number of conflicts and combinations of activity duration and traffic volume. A DOT can use these plots to determine, for example, if it should conduct a moving work activity for a short duration when the volume is high or for a longer duration when the volume is lower.

Funding Sources:
Midwest Transportation Center
Smart Work Zone Deployment Initiative ($50,000.00)
USDOT/OST-R ($50,185.00)
Total: $100,185.00

Contract Number: DTRT13-G-UTC37

About the research

Many work zones require lane closures, and road users need to be notified of these closures through appropriate upstream signage. A literature review prepared for this study found several previous investigations indicating insufficient comprehension of the U.S. standard lane closure sign (designated in the Manual on Uniform Traffic Control Devices for Streets and Highways [MUTCD] as W4-2) and similar signs used internationally. The W4-2 sign is also unsuitable for signing interior lane closures on roadways with three or more lanes.

Driver comprehension of several alternative sign faces was tested through a survey using the ANSI Z535.3 process and was followed by a driving simulator study. The driver comprehension survey suggests that an Upward Drop Arrow design is a promising alternative to the existing W4-2 sign for sites where two upstream lanes are reduced to one lane in the work zone. In addition, one-arrow-per-lane signs developed as Americanized versions of the Vienna Convention G12a sign template are a promising option for interior lane closures on multi-lane roadway segments.

A driving simulator study compared the W4-2, a MERGE text sign with a horizontal arrow, and an Americanized version of the Vienna Convention G12a sign. In terms of sign comprehension, the W4-2 was the least understood of the three signs. The W4-2 resulted in more late merge maneuvers than the other two signs. Field evaluation of the Upward Drop Arrow and Americanized G12a signs is recommended as a follow-up to this study.

Funding Sources:
Midwest Transportation Center
Smart Work Zone Deployment Initiative ($23,714.00)
University of Missouri – Columbia ($13,984.00)
USDOT/OST-R ($74,022.00)
Total: $111,720.00

Contract Number: DTRT13-G-UTC37

About the research

Traditionally, traffic impacts of work zones have been assessed using planning software such as Quick Zone, custom spreadsheets, and others. These software programs generate delay, queuing, and other mobility measures but are difficult to validate due to the lack of field data necessary for validation. One alternative approach for assessing the travel time impacts of a work zone is through data mining. Historical data of travel times observed during work zones and normal conditions can be used for work zone planning and scheduling.

This project developed a prototype tool using historical data for work zones in the St. Louis region in Missouri. Data from 782 work zones on I-70, I-270, and MO 141 that occurred between January 2014 and October 2015 were used. Several data sources were utilized in this project. These included electronic alerts of work zone information such as start and end times, location, lane closure information, and travel times. Spatially, the data included the work zone segment, two upstream segments, and all segments within a 2-mile radius of the work zone. Two delay measures were used for quantifying impact of work zones on freeway segments: travel time delay based on historical average travel times for the segment and travel time delay based on historical 15th percentile travel time values.

A model was developed to estimate travel times for planned work zones at sites that may not have sufficient historical work zone data. The Random Forests technique was used to develop the model. Separate models were developed for interstate and arterial work zones using historical travel times and speed profiles, work zone and upstream segment lengths, lane closure information, and work zone schedule. The predicted travel times were then utilized to compute delays. A prototype of the data-driven traffic assessment tool was developed. The predicted travel times for both interstate and arterial work zones were within 5% error.

For demonstration purposes, the scope of the prototype was limited to two interstate corridors and one arterial corridor. The tool uses four types of input information: work zone location, roadway direction, work zone duration, and work zone type and lane closure information. The tool then uses this information to mine the historical data to identify any work zones that occurred at the same location in the past. If a match is found, the historical data is utilized to generate the expected delay measures. If a match is not found, the Random Forests prediction model is used to generate the expected delay measures.

Funding Sources:
Midwest Transportation Center
Smart Work Zone Deployment Initiative ($50,003.00)
University of Missouri – Columbia ($13,374.00)
USDOT/OST-R ($84,158.00)
Total: $147,535.00

Contract Number: DTRT13-G-UTC37

About the research

Highway construction is among the most dangerous industries in the US. Internal traffic control design, along with how construction equipment and vehicles interact with the traveling public, have a significant effect on how safe a highway construction work zone can be.

An integrated approach was taken to research work-zone safety issues and mobility, including input from many personnel, ranging from roadway designers to construction laborers and equipment operators. The research team analyzed crash data from Iowa work-zone incident reports and Occupational Safety and Health Administration data for the industry in conjunction with the results of personal interviews, a targeted work-zone ingress and egress survey, and a work-zone pilot project.

About the research

Work zones by nature present transitions and changes to motorists’ expectations. Given these conditions, providing proper guidance to motorists is critical.

With respect to pavement markings, the challenge is to provide sufficient markings but in a temporary setting. Various pavement-marking products are currently in use within work zones; however, their effectiveness and cost can vary widely.

This research evaluated the effectiveness of several common removable pavement marking products in terms of daytime presence, retroreflectivity, and removability. The evaluation was completed on an active work zone in central Iowa and included both white and yellow edge-line markings within the taper and crossover sections of a work zone.

Presence was evaluated in terms of the amount of product remaining at the end of the evaluation period. Retroreflectivity was measured using a 30 meter geometry retroreflectometer. Product removal was evaluated in terms of internal tape strength, adhesive bond, and the amount of discernible markings after removal based on the American Association of State Highway and Transportation Officials (AASHTO) National Transportation Product Evaluation Program(NTPEP).

Findings showed that performance of temporary pavement marking materials is highly dependent on the surface characteristics on which they are being placed, the amount of traffic traversing the material, and the marking material used. All tape products met the Iowa Department of Transportation (DOT) minimum retroreflectivity standard throughout the duration of the work zone. With a few exceptions, due to marking location, the tape products were removed easily with minimal to moderate discernible markings remaining.

Based on these findings, the research team recommends that the Iowa DOT consider using temporary pavement marking tape products for all markings within the crossover section of the work zone, given this area receives the most wear from vehicle weaving actions and also presents the most challenges for maintaining the markings. The team also notes that removable paint products are rapidly evolving and are a potentially promising alternative in terms of installation, cost, and removal (no scaring), and are worth investigating further.