Work Zone Speed Limit Research Articles

Comparison of Analytical and Simulation Results for One-Lane Operation on Low-Volume Two-Lane Highway

Work zones on two-lane highways with one lane closed require sharing the open lane with traffic from the closed directions. In such work zones, traffic control resembles operating a two-phase traffic signal and, in rare cases, a three-phase traffic signal. Temporary traffic signals (or flaggers) allow the open lane to be used in an alternating manner. Signal timing (green times and cycle length) of the temporary traffic lights directly affects the delay and queue in the work zones. Delay and queue computations must consider queue build up that often happens in oversaturated conditions. Another influential variable is the average operating speed of the work zone. The operating speed is affected by the work zone speed limit, work intensity, speed control technique, lane and shoulder widths, acceleration capability of vehicles, and work zone length. WorkZoneQ-Pro (WZQ-Pro) is developed with a new signal timing method that considers the above-mentioned factors. The procedure can handle multiple hours of analysis with two- or three-phase signal operations. Test scenarios are real-world work zone examples from three different U.S. states that were used to compute signal time variables and use them to compute queue and delay. These values were also computed using Highway Capacity Manual (HCM) 2016 procedures and are compared. In addition, the computed values were input into Vissim simulation software, and the results were compared. It showed that the WZQ-Pro results are reasonably close to Vissim simulation results, and that further validated that an acceptable agreement existed between the analytical and simulation results.

How effective is reducing traffic speed for safer work zones? Methodology and a case study in Pennsylvania

Transportation agencies post and enforce reduced speed limits in work zones to ensure work zone safety, since traffic speed is found to be associated with work zone crash risks. However, prior findings on the relationship between speed and crash rate in work zones are inconsistent. This may be attributed to the methods of statistical associations between traffic speed and crash risks that do not necessarily discover true causal relations. In fact, work zone presence could lead to the reduction of actual traffic speed that influences crash risks, where it may also directly impose effects on crash risks as a result of work zone configurations. The actual traffic speed (not posted speed limit) is also known as a “mediator” where work zones can indirectly impact the crash risks. It is challenging to rigorously separate the causal effect of traffic speed on work zone crash risk from that directly caused by work zones. The underlying causal relation could help to determine what reduced post speed limit (with enforcement) is necessary to ensure work zone safety under the most desired “actual traffic speed”. This study proposes to use the sequential g-estimation and the regression discontinuity design to estimate the controlled direct effect of traffic speed on work zone crashes. Two research gaps are identified and filled: inaccurate inferences of the effect of reduced speed limit in work zones as a result of ignoring (1) potential post-treatment bias since traffic speed is a mediator; and (2) potential confounding bias caused by unobservable roadway characteristics. The proposed methodology was applied to 4008 work zones in Pennsylvania from 2015 to 2017, and the results were validated through a series of robustness tests. The results indicate that the direct causal effect of the presence of work zones on crash risk is significantly positive when the traffic speed is relatively low (i.e., lower than 55 mph in this case study), while traffic speed has a positive causal effect on crash occurrences when the actual traffic speed is high (i.e., greater or equal to 55 mph). It suggests that strictly enforcing reduced posted speed limits in work zones is particularly effective when the actual traffic speed is greater than 55 mph. This is particularly true on roadways with high traffic volume (i.e., AADT > 20,000 vehicles per day), long, and daytime work zones (i.e., > 3000 m). On the other hand, the effect of enforcing reduced speed on work zone safety is unclear when the actual speed is already low. In this case, improving work zone configurations and driving behaviors may be more effective in reducing crash risks.

Review of Methods for Estimating Construction Work Zone Capacity

Road reconstruction and the resulting work zones are considered as a major source of traffic congestion and delays on freeways. The roadway capacity is decreased as a result of a reduced number of traffic lanes, narrower lanes, and work zone speed limits. Accurate prediction of construction work zone capacity helps traffic engineers to have a better estimation of the traffic flow characteristics. To this end, multiple methodologies have been developed to quantify the impacts of work zones on traffic flow. This paper presents a critical review of the three types of approaches to estimating construction work zone capacities, including parametric, non-parametric, and simulation. Then the most commonly considered factors and their frequency are presented. It also performs a detailed review of the approaches, their objectives, and weaknesses. Lastly, it provides recommendations for future research. The presented work could help researchers in the area of work zone capacity estimation by presenting all the previous methodologies in one place.

Assessing driving behavior upstream of work zones by detecting response points in speed profile: A naturalistic driving study

Objective: To assess driving behavior when presented with different work zone features such as signs. Driving behavior upstream of a work zone is of interest since this is the point where drivers need to slow or react to upcoming conflicts such as lane closures, congested traffic, or presence of workers and equipment.Methods: Using 299 time series traces from four-lane roadways with both shoulder and lane closure scenario from the naturalistic driving study, this study analyzed driving behavior by detecting response points within the advance warning area from the first sign to the start of work zone. Response point was defined as the point where drivers reduced speed by a certain threshold. A mixed effect logistic model was developed to assess the relationship between driver response and work zone characteristics.Results: Results indicated the first work zone sign a driver encountered in the immediate area upstream of the work zone was not significantly likely to elicit a driver response. The model found lane ends, speed limit, and active changeable message signs (CMS) as statistically significant. Since more than one sign can be legible to the driver at the same time, the effect of overlapping signs was evaluated, but was not found to have significant effect on the driver response. In general, drivers were more likely to show a response to the signs the closer they got to the start of the work zone. Static work zone speed limit and dynamic speed feedback signs were both found to be more likely to elicit a response as compared to normal speed limit signs (non-work zone related). Drivers who were traveling over the posted speed limit were more likely to show response at any given work zone signs with the exception of the first sign. In addition, driver distraction, and driver information like age, gender, experience and other environmental factors were not found to be significant in the model.Conclusions: Overall, drivers were likely to show a response at the lane ends, work zone speed limit signs, and speed feedback signs.

Effects of roadwork characteristics and drivers’ individual differences on speed preferences in a rural work zone

Work zone safety from a psychological perspective has received little attention in scientific literature. Therefore, the present study aims to explore the influence of roadwork characteristics and drivers’ individual differences in terms of personality traits and self-assessment of driving skills on speed preferences in a rural work zone. Eight hundred forty-five Norwegian drivers stated their preferred speed for ten pictures of a rural work zone with a 50 km/h reduced speed limit without knowing the speed limit. The results showed that the preferred speeds were greater than the actual reduced speed limit for all pictures. The standard deviations were quite high (from 11 to 14 km/h), indicating that drivers have a rather high variation in preferred speeds. A multilevel model was used to analyse the effects of the variables on speed preference. The results indicated that preferred speeds increased with age, higher scores on the normlessness scale, and higher self-assessment of own driving skills. As for the roadwork characteristics, speed increased with the presence of road markings by 11 km/h, while it decreased by 9 km/h with the presence of road delineators and by 5 km/h with barriers. Implications for respect for the reduced speed limits in work zones were discussed, and recommendations of other countermeasures were presented.

Use of Portable and Dynamic Variable Speed Limits in Construction Zones

The Utah Department of Transportation (UDOT) implemented dynamic management of portable variable speed limit (PVSL) technology to reduce regulatory speed limits through an active work space (AWS). UDOT also developed and tested an intelligent system approach to alter speed limits in construction work zones. The goal of the PVSL system was to provide a portable and dynamic system that was easy for construction personnel to use to prudently reduce speeds within an AWS and make construction work zones safer for workers and the traveling public, while limiting the need to reduce speed throughout the AWS, rather than the entire construction work zone. This was achieved through temporary regulatory reductions in driver speeds within the immediate boundary of an AWS when workers were on site and exposed to the danger of errant vehicles during active construction. The system also raises speed limits when workers were not present. This PVSL system used a dynamic variable speed limit (VSL) algorithm to raise and lower the regulatory speed limits. The PVSL system also provided a queue warning algorithm that operated independent of the VSL algorithm to control messages posted on the portable variable message sign (PVMS) trailers to disseminate dynamic information to drivers. UDOT has completed 2 years of PVSL system deployment testing in four separate construction work zones to evaluate the effectiveness of the system. This paper highlights key elements that guided development of the PVSL system, along with the successful results from deployment of the system.

Evaluation of variable advisory speed limits in congested work zones

ABSTRACTThe effectiveness of variable “advisory” speed limit (VASL) systems in congested urban work zones was investigated. Except for one publication, all previous studies focused on regulatory speed limit systems. This study used a comprehensive set of performance measures to investigate VASL effectiveness. Four congested work zones with lanes reduced from four to three lanes on Interstate 270 in St. Louis, Missouri, were selected for empirical and simulation analysis. The empirical analysis showed that VASL were effective in slowing down drivers gradually as they approached the work zone, thus reducing any sudden speed changes. Simulation analysis showed that operationally, the use of VASL resulted in: a 39% to 53% decrease in average queue length, a 7% to 11% reduction in throughput, a 4% to 8% increase in travel time. The use of VASL achieved a decrease in the standard deviation of speeds at the taper and 1-mile upstream of the work zone. The maximum speed differences also decreased up to 10 mph with VASL. A new VASL algorithm investigated in the study showed significant improvements in mobility and safety performance compared to the original field algorithm. The new algorithm made promising improvements in safety—a 30% reduction in rear-end conflicts and a 20% reduction in lane changing conflicts as compared to the without VASL condition. The new VASL algorithm also decreased the queue length, further improving the overall safety in congested work zones. Thus, it is possible to design a VASL system that improves traffic and safety in congested work zones.

Motorists' Speed Response to Nonvariable and Variable Work Zone Speed Limits and Other Work Zone Conditions

Transportation professionals view the setting of appropriate regulatory speed limits on public roads, including those under repair or reconstruction, as an important tool in promoting safe and efficient operations. The Ohio Department of Transportation sponsored a study to evaluate its work zone speed zoning processes. Researchers observed motorists' speed choices upstream of and adjacent to several combinations of work zone conditions and factors that were used to justify reduced speed limits in Ohio work zones. Researchers also observed motorists' speed choices upstream of and within pilot variable work zone speed zones. Researchers confirmed that motorists reduced their speed only if they clearly perceived a need to do so. Therefore, whenever possible, the first work zone speed limit sign should be installed within view of a work zone condition. In general, the speed reduction downstream of the first nonvariable and variable work zone speed limit signs ranged from 1 to 6 mph and 3 to 11 mph, respectively. In addition, researchers found that the speed reduction on entering a lane shift, within a lane closure, and on entering a median crossover ranged from 4 to 15 mph. On the basis of previous research and the results of the studies documented in this paper, the research team developed work zone speed zone guidelines for multi-lane highways with original posted speed limits greater than or equal to 55 mph. Researchers also made recommendations for where variable work zone speed zoning should be considered.

Assessment of Speed Limit Locations Using Crowdsourced Probe Vehicle Data

Recently there has been an increased interest in using technology to apply variable speed limit techniques to Interstate roadways. An important component of changing speed limit signs (or variable speed limit signs) is an outcome assessment that collects measured data for understanding the effect on the network. For 265 mi of I-65 in Indiana, the speed limit locations were geolocated and paired with crowdsourced probe vehicle data to develop metrics that engineers and decision makers could use to optimize speed limit placement. Four case studies show the effect of different types of speed reduction and opportunities to improve the current placement. The visual performance measures described in this paper are readily deployable and scalable to any freeway in the country for assessing variable speed limits, work zone speed limits, and static speed limits.

Incorporating work zone configuration factors into speed‐flow and capacity models

SummaryThis study aims to develop work zone speed‐flow and capacity models, which incorporate work zone configuration factors including the number of work zones, geometrical alignment, work zone speed limit, and work zone length. On the basis of the traffic data from six work zone sites with various work zone configurations, two nonlinear traffic speed and flow models including work zone configuration factors are developed for the uncongested and congested traffic conditions, respectively. A work zone capacity model is proposed on the basis of the two models. The three models can further be used to examine the effects of work zone configuration factors on the speed‐flow relationship and capacity at work zones. Results show that traffic speed, traffic flow, and work zone capacity increase with the posted speed limit. Traffic speed under uncongested conditions decreases with the geometric alignment, the number of work zones, work zone length, and heavy vehicle percentage. Under congested conditions, the increase of the number of work zones is found to exhibit a larger negative impact on the traffic flow than the increase of geometric alignment. The number of work zones is also found to have the largest negative impacts on work zone capacity, followed by the geometric alignment. Short work zone length exhibits a relatively minor contribution to increasing work zone capacity. Copyright © 2014 John Wiley & Sons, Ltd.

Speed limit effectiveness in short-term rural interstate work zones

Average speed and speed variance are two characteristics of traffic flow that affect accident rates and severity near work zones. Operationally, work zones account for approximately 24% of the non-recurring delay. A policy for work zone speed limits has to delicately balance the safety and the efficiency impacts. If speeds are set too low, then avoidable congestion and speed violations might result. If speeds are set too high then, again, safety may be compromised. In this paper, results from field studies conducted on three Interstate 70 maintenance short-term work zones in rural Missouri are presented for three different speed limit scenarios: no posted speed limit reduction, 10 mph posted speed limit reduction, and 20 mph posted speed limit reduction. The 85th percentile speeds and standard deviation of speed were found to be 81 and 10 mph; 62 and 8 mph; and 48 and 6 mph, respectively for the three scenarios. The differences in 85th percentile speed and standard deviation of speed among all three scenarios were statistically significant. The per cent of drivers who exceed speed limit by over 10 mph were 15·4, 4·8, and 0·9%, respectively. Thus a reduction in posted speed limit was effective in reducing prevailing speeds and speed variances in short-term work zones in rural Missouri.

Effects of environment, vehicle and driver characteristics on risky driving behavior at work zones

This study aims to analyze the effects of environment, vehicle and driver characteristics on the risky driving behavior at work zones. A decision tree is developed using the classification and regression tree (CART) algorithm to graphically display the relationship between the risky driving behavior and its influencing factors. This approach could avoid the inherent problems occurred in the conventional logistic regression models and further improve the model prediction accuracy. Based on the Michigan M-94/I-94/I-94BL/I-94BR highway work zone driving behavior data, the decision tree comprising 33 leaf nodes is built. Bad weather, poor road and light conditions, partial/no access control, no traffic control devices, turning left/right and driving in an old vehicle are found to be associated with the risky driving behavior at work zones. The middle-aged drivers, who are going straight ahead in their vehicles with medium service time and equipped with an airbag system, are more likely to take risky behavior at lower work zone speed limits. Further, the middle-aged male drivers engage in risky driving behavior more frequently than the middle-aged female drivers. The number of lanes exhibits opposing effects on risky behavior under different traveling conditions. More specifically, the risky driving behavior is associated with the single-lane road under bad light or weather conditions while drivers are more likely to engage in risky behavior on the multi-lane road under good light conditions.

The effect of in-vehicle warning systems on speed compliance in work zones

The purpose of this research was to evaluate the effectiveness of augmented in-vehicle speed warnings on driver behavior in work zones. The influence of three device configurations were examined as the drivers entered a work zone which was presented in a simulated driving environment. The first configuration was a control condition which used only traditional signage. The second condition had the addition of a visual in-vehicle warning while the final condition had the addition of an auditory in-vehicle warning. Results indicated that adding in-vehicle warnings did affect driver compliance to the work zone speed limit. Participants in the audio warning condition responded more quickly to the warning than those in the visual condition. Both augmented warning configurations differed significantly and were each respectively different from the drivers in the control condition. Based on these results we suggest a combination of in-vehicle warnings. Upon entry of the work zone we suggest a combined audio and visual warning message. However, after the initial entry phase, a visual warning message shows greater promise for the on-going modulation of driver speed transit.

Field Evaluation of Motorist Reactions to Reduced Work Zone Speed Limits and Other Work Zone Conditions

Many factors are taken into consideration in procedures to determine whether a reduced regulatory speed limit in a work zone is warranted. Low levels of compliance with work zone speed limits continue to show, however, that there is a disconnect between procedures to establish regulatory speed limits and motorists’ actual choice of speed in work zones. An improved understanding of how the conditions used to justify reduced speed limits in work zones actually affect speeds could improve the speed limit selection process. To address this need, researchers conducted field studies in Texas work zones to determine motorists’ speed choices adjacent to conditions that were used to warrant reduced speed limits. On the basis of the findings, researchers concluded the following: when no work zone conditions were apparent, speeds downstream of reduced work zone speed limit signs decreased only slightly, independent of the speed limit reduction. Motorists reduced their speeds in work zones when they perceived a need to do so. How much speed was reduced, however, appeared to depend on the normal operating speed of the roadway, the imposing nature of the situation, and enforcement activities. Some work zone conditions used to justify reduced speed limits were not adequately perceived by motorists. Thus it was these conditions that were most in need of enforcement, because motorists were less likely to reduce their speeds voluntarily. Reduced work zone speed limits that were left in place when conditions did not warrant them led to high levels of noncompliance.

Evaluation of Spatial and Temporal Speed Limit Compliance in Highway Work Zones

Typically, speed limits are reduced in work zones to safely accommodate construction activities and motorists on the roadway. This paper presents a methodology to evaluate the temporal and spatial effects of techniques designed to encourage compliance with work zone speed limits. The evaluations were performed over short and long segments within and adjacent to an Interstate construction work zone in suburban Indianapolis, Indiana, with the use of vehicle probe data. Space mean speed was measured by using 13 Bluetooth probe data acquisition stations, which provided a random sample of unique identifiers for approximately 11% of the passing vehicles. These space mean speed data were used to compute a series of comparisons between a day with no enforcement activity and a day with exceptionally high enforcement. During enforcement, the space mean speed decreased by approximately 5 mph throughout the 12.2-mi study segment. Within 30 min after the enforcement detail ended, however, space mean speeds increased, and there was no statistically significant residual impact on the space mean speed. Even at the absolute peak of enforcement, 75% of the probe vehicles exceeded the speed limit in all but one of the segments that had a posted speed limit of 45 mph. In addition, 25% of the probe vehicles exceeded the posted limit by more than 5 mph in all 45-mph segments during peak enforcement. The study is perhaps the largest ever conducted with respect to concurrent enforcement and extensive space mean measurement. The data represent an upper bound on the impact of enforcement activity on work zone speeds and should be of interest to public agencies as they consider compliance techniques.

The Effect of In-Vehicle Warning Systems on Speed Compliance in Work Zones

The purpose of this research was to evaluate the effectiveness of augmented in-vehicle information on driver behavior in work zones. In-vehicle information systems (IVISs) can increase driver awareness to an oncoming change in traffic flow and provide specific guidelines for driving speed requirements, for example. Three variations of IVISs were examined as the drivers entered a work zone in a simulated driving environment. The first was a control condition, which used only traditional signage and no IVIS. The second condition had the addition of visual in-vehicle warnings and the final condition the addition of auditory in-vehicle warnings. Results indicated that adding in-vehicle warnings did affect driver compliance to the work zone speed limit. Further, participants in the audio warning condition responded more quickly to the warning than in the visual condition. These were each respectively different from the drivers in the control condition. Conclusions and implications are discussed.

Motorist Understanding of Alternative Displays for Speed Limits in Work Zones

In Texas, speed limits for short-term work zones are reduced speed limits that are posted only when work activity is present. When work activity is not present, the reduced speed limit signs are to be removed or covered; the legal speed limit for that segment reverts to the normal zone speed limit. The major challenge of speed limits for short-term work zones is the daily process of installing and removing, or uncovering and covering, signs. In this study, researchers conducted a laptop-based laboratory survey to determine (a) motorists' understanding and opinions of alternative short-term signs for speed limits in work zones and the enforceability of limits, (b) the success of the orange or white light-emitting diode (LED) color used on electronic speed limit (ESL) signs and portable changeable message signs (PCMSs) in indicating to motorists that they were advisory or regulatory signs, and (c) motorists' preference for short-term speed limit displays. The four categories of signs included in the survey were static work zone signs, ESL signs, speed limits displayed on PCMSs, and “Your Speed” signs (distracters). On the basis of the results obtained from this survey, researchers recommend the use of ESL signs and flexible roll-up signs for speed limits in static work zones for displaying speed limits in short-term work zones. To ensure that the speed limit displayed on ESL signs is considered a regulatory speed limit, the changeable display should be composed of white LEDs.

Devices to Implement Short-Term Speed Limits in Texas Work Zones

In Texas, speed limits for short-term (less than 12 consecutive h) work zones are used when workers or equipment are not behind a concrete barrier, work activity is within 15 ft of the pavement edge, or work is actually occurring on the pavement. In these situations, speed limit signs for short-term work zones should be posted and visible to the motorists only when work activity is present and covered or removed when no work activity is present. Covering or removing signs can be a tedious task to complete daily or weekly. In addition, this task may interfere with normal traffic flow and expose workers to traffic hazards. Some contractors choose not to cover or remove signs; others simply forget: thus speed limits for short-term regulatory work zones extend into time periods with no apparent need for a speed limit reduction. New sign technologies may simplify the implementation process speed limits for short-term work zones and could enhance the use of such speed limits in general. However, such technologies have not been used extensively for speed limits in work zones in Texas. Thus, researchers at the Texas Transportation Institute conducted field studies to determine the operational effectiveness of electronic speed limit signs and flexible roll-up speed limit for work zones signs. The researchers recommended the use of both types of signs.

Speed Photo–Radar Enforcement and Its Effects on Speed in Work Zones

Automated speed photo–radar enforcement (SPE) in work zones was implemented for the first time in the United States in Illinois. This paper presents the results of the effectiveness of SPE on the basis of three data sets collected in two work zones. SPE was effective in reducing the average speed and increasing compliance with the work zone speed limit in all three data sets. In almost all cases in which SPE was implemented, the average speeds were significantly lower than the work zone speed limit. The average free-flowing speed of cars was reduced by 4.2 to 7.9 mph, and that of trucks by 3.4 to 6.9 mph. SPE reduced the percentage of cars and heavy vehicles exceeding the speed limit significantly. The percentages of free-flowing cars exceeding the speed limit were reduced from 39.8% to 8.3% in Data Set 1, from 30.4% to 4.2% in Data Set 2, and from 93.2% to 45.5% in Data Set 3. The percentages of free-flowing heavy vehicles exceeding the speed limit were reduced from 17.3% to 4.2% in Data Set 1; from 6.1% to 1.2% in Data Set 2; and from 69.2% to 13.9% in Data Set 3. Trucks did not exceed the speed limit by more than 10 mph in any of the data sets when SPE was implemented. In two data sets no cars exceeded the speed limit by more than 10 mph, while in the third data set only 2.5% did. Field data were also collected after the SPE van left the work zone to examine the halo (temporal) effects of SPE. SPE had a halo effect of 1.8∼2.7 mph on free-flowing trucks in one work zone but none in the other work zone. The halo effect of SPE on free-flowing cars was a limited 1.2 mph on the shoulder lane in only one data set.

Automated Speed Photo Enforcement Effects on Speeds in Work Zones

Automated speed enforcement in construction zones has the potential to increase compliance with the speed limit and improve safety. The effectiveness of speed photo enforcement (SPE) (by radar) in reducing speeds and increasing speed limit compliance in work zones was evaluated for the first time in the United States, at Illinois work zones. Details are presented on SPE implementation and its effectiveness at the point it was stationed and at a downstream location in a work zone. Speed data were collected at the location of SPE and at a location 1.5 mi downstream in the work zone to determine the point and spatial effects of SPE. Speeds were measured for free-flowing and platooned cars and heavy vehicles in shoulder and median lanes. Results showed that SPE is effective in reducing the average speed and increasing compliance with work zone speed limit. The SPE reduced speed in the median lane more than in the shoulder lane, as expected. In addition, the speed of free-flowing vehicles was reduced more than for platooned vehicles. The reduction of the mean speed varied from 3.2 to 7.3 mph. The percentage of vehicles exceeding the speed limit near SPE was reduced from about 40% to 8% for free-flowing cars and from 17% to 4% for free-flowing heavy vehicles. Near the SPE van, none of the cars exceeded the speed limit by more than 10 mph, and none of the heavy vehicles exceeded it by more than 5 mph. The data also showed a mixed spatial effect for SPE. At the downstream location, the speed reduction for cars was not significant, while it varied from 0.9 to 2.5 mph for heavy vehicles.