Institute for Transportation

About the research

The speed monitoring display (SMD) developed in the late 1970s is one of the promising technologies that have been successfully applied both in the U.S. and abroad. The SMD informs drivers of their speeds and thereby encourages them to slow down if they are traveling above the speed limit. The objective of the system is to reduce the speed of traffic and increase speed limit compliance.

The primary objective of this evaluation was to assess the long-term effectiveness of SMDs in long-term work zones on rural interstate highways. To achieve this goal, three SMDs were deployed in a work zone area on I-80 near Lincoln, Nebraska. The effectiveness of the system was studied over a period of five weeks.

The SMDs were found to be effective in lowering speeds and increasing the uniformity of speeds over a period of five weeks

Vendor: Speed Measurement Labs

About the research

The D-25 Speed Advisory Sign System was intended to warn drivers of stopped or slow-moving traffic ahead and thereby enable them to reduce their speeds and avoid rear-end crashes with these vehicles. The three speed trailers were operated independently, and the speed displays showed the speed of the downstream traffic. When a traffic slowdown was detected, the strobe lights began flashing. When there was no slowdown, the strobe lights were off, and either the speed of traffic downstream or the work zone speed limit was displayed, which ever was lower. The system deployed for the purpose of the field evaluation consisted of three speed trailers placed at approximately ¼-mile interval in advance of a work zone on Interstate 80 near Lincoln, Nebraska. The results of the analysis indicated that the speed messages were effective in reducing the speed of vehicles approaching queued traffic during time periods when congestion was building. The speed profiles observed during the operation of the speed advisory system were generally smoother than those observed before system deployment. Before the trailers were deployed, vehicles began decelerating later but more intensively than after their deployment. Deceleration pattern at the trailer farthest from the lane closure taper (trailer 3) has completely changed when the speed trailer began displaying speed messages. Before system deployment most drivers only slightly reduced their speed between the first two speed measurement points, and they mostly reduced their speed between the second and third measurement points. After system deployment, motorists at trailer 3 decelerated more before they reached the speed trailer than after they passed it. Due to the limited time available for the field studies the long-term effectiveness of the speed advisory system could not be determined.

Vendor: MPH Industries

About the research

The work zone speed advisory system (WZSAS) is designed to provide real-time speed advisory information to drivers by means of portable CMSs strategically located in advance of diversion points upstream of a work zone. This study evaluated the effectiveness of the WZSAS in encouraging traffic diversion when there was congestion in the work zone. The system was evaluated using data collected from the control system’s logs, field studies, user surveys, and system observations.

Traffic demands were estimated from traffic flow and density data observed at the two camera locations during time periods before and after the deployment of the WZSAS system. The comparison between the “before” and “after” demands was made using data from every three-hour peak flow period during the study. It was found that the total peak-period demands did not change significantly in response to the speed messages. The WZSAS system did not significantly increase vehicle diversion under the traffic conditions observed during the study period. However, it should be noted that the system might be more effective under heavier traffic demands and more severe congestions.

Vendor: National ITS

About the research

Real-Time CMS Control (RTCMSC) is an enroute traveler information system whereby real-time traffic-responsive information is provided to drivers by means of a changeable message sign (CMS) strategically placed in advance of a diversion point upstream of the work zone. The objective of the system is to advise drivers of a work zone ahead and encourage them to divert to an alternate route when there is congestion in the work zone.

The RTCMSC was effective in encouraging some drivers to divert to an alternate route when congestion was detected in the work zone. Although its effectiveness was limited to about 4.5 percent diversion, the diversion message displayed on the CMS had a statistically significant effect (“=0.05) on the percentage of traffic on the exit ramp. The effect of traffic volume during the study period was not statistically significant.

Vendor: Brown Traffic

About the research

The SpeedGuard radar speed reporting system is a speed monitoring display which informs drivers of their speeds and thereby encourages them to slow down if they are traveling above the speed limit. The objective of the system is to reduce the speed of traffic and increase speed limit compliance. Statistically significant reductions in speeds and improvements in the uniformity of speeds were observed in both passenger cars and non-passenger cars after the deployment of the SpeedGuard system. The 85th-percentile speed, upper limit of the pace, and mean of the highest 15 percent of speeds were reduced by 4 or 5 mph and dropped to or below the 55-mph speed limit. The percentages of passenger cars and non-passenger cars complying with the 55-mph speed limit increased 17 and 15 points to 91 and 90 percent, respectively. The system proved to be effect at reducing speeds and increasing speed uniformity in the study context. It should be noted that data collection included only 7 hours of data after system deployment, and no data was available with respect to the persistence of the speed reductions farther downstream.

Vendor: Speed Measurement Labs

About the research

The ADAPTIR is a portable, condition-responsive work zone traffic control system which is capable of providing drivers with real-time information about work zone traffic conditions via VMS and highway advisory radio (HAR). It was deployed in a work zone on I-80 between Lincoln and Omaha during the summer of 1999. The system is intended to provide warning to drivers of slower speeds and delays within the work zone, and encourage them to use caution and take alternate routes if possible. Various measures of effectiveness were employed to characterize the effect of the system on traffic and driver decisions. Traffic speed and lane distribution on the approach to the work zone were measured before and after the deployment of the ADAPTIR. The number of forced merges were obtained from video footage near the taper. Speeds were compared with advisory speeds to determine compliance. Diversion point volumes were logged to determine if drivers took alternate routes because of the system. Finally, a driver survey was conducted. Crash data was also examined, using a regression technique to compare crashes with and without the system. The systems use did not significantly affect any of the parameters with the exception of speed. The speed advisory message did have a effect on speeds, and the effect was stronger for signs located closer to the work zone.

Vendor: Scientex Corp.

About the research

Crashworthy, work-zone, portable sign support systems accepted under NCHRP Report No. 350 were analyzed to predict their safety peformance according to the TL-3 MASH evaluation criteria. An analysis was conducted to determine which hardware parameters of sign support systems would likely contribute to the safety performance with MASH.

The acuracy of the method was evaluated through full-scale crash testing. Four full-scale crash tests were conducted with a pickup truck. Two tall-mounted, sign support systems with aluminum sign panels failed the MASH criteria due to windshield penetration. One low-mounted system with a vinyl, roll-up sign panel failed the MASH criteria due to windshield and floorboard penetration. Another low-mounted system with an aluminum sign panel successfully met the MASH criteria. Four full-scale crash tests were conducted with a small passenger car. The low-mounted tripod system with an aluminum sign panel failed the MASH criteria due to windshield penetration. One low-mounted system with aluminum sign panel failed the MASH criteria due to excessive windshield deformation, and another similar system passed the MASH criteria. The low-mounted system with a vinyl, roll-up sign panel successfully met the MASH criteria.

Hardware parameters of work-zone sign support systems that were determined to be important for failure with MASH include sign panel material, the height to the top of the mast, the presence of flags, sign-locking mechanism, base layout and system orientation. Flowcharts were provided to assist manufacturers when designing new sign support systems.

About the research

Often, road construction causes the need to create a work zone. In these scenarios, portable concrete barriers (PCBs) are typically installed to shield workers and equipment from errant vehicles as well as prevent motorists from striking other roadside hazards. For an existing W-beam guardrail system installed adjacent to the roadway and near the work zone, guardrail sections are removed in order to place the portable concrete barrier system. The focus of this research study was to develop a proper stiffness transition between W-beam guardrail and portable concrete barrier systems. This research effort was accomplished through development and refinement of design concepts using computer simulation with LS-DYNA. Several design concepts were simulated, and design metrics were used to evaluate and refine each concept. These concepts were then analyzed and ranked based on feasibility, likelihood of success, and ease of installation. The rankings were presented to the Technical Advisory Committee (TAC) for selection of a preferred design alternative. Next, a Critical Impact Point (CIP) study was conducted, while additional analyses were performed to determine the critical attachment location and a reduced installation length for the portable concrete barriers. Finally, an additional simulation effort was conducted in order to evaluate the safety performance of the transition system under reverse-direction impact scenarios as well as to select the CIP. Recommendations were also provided for conducting a Phase II study and evaluating the nested MGS configuration using three Test Level 3 (TL-3) full-scale crash tests according to the criteria provided in the Manual for Assessing Safety Hardware, as published by the American Association of Safety Highway and Transportation Officials (AASHTO).

About the research

Portable concrete barrier (PCB) systems are often used to redirect errant vehicles through a combination of inertial resistance, lateral friction loads, and tensile loads developed from the mass and friction of the barrier segments. State departments of transportation (DOTs) and other end users may wish to utilize minimal length PCB installations to shield a hazard or work zone or limit the number of barriers required on the upstream and downstream ends to reduce overall system length. However, concerns with the performance of shorter PCB installations include increased lateral deflections and working widths and barrier pocketing. Additionally, no impact testing has been performed near the upstream or downstream ends of the free-standing PCB system to determine the limits of the length of need (LON) of the system. These impacts may increase the potential for gating through the system, pocketing, rapid deceleration, and/or vehicle instability. The objective of this research study was to investigate and evaluate the safety performance of a previously developed F-shape PCB system to determine minimum system length and the number of barriers required for the beginning and end of the LON. LS-DYNA simulation modeling was applied to determine potential beginning and end of LON points on reduced system lengths to select a configuration for full-scale testing and evaluation of a minimum length PCB system. A 100-ft long PCB installation was selected, and full-scale crash testing was conducted on the beginning and end of LON of the reduced length system. Test no. NELON-1 was conducted to MASH test designation 3-35 criteria on the beginning of LON of the 100-ft long PCB installation, and the vehicle was safely redirected. Test no. NELON-2 was conducted to modified MASH test designation no. 3-37 criteria on the end of LON of the 100-ft long PCB installation, but the test was deemed a failure as the vehicle demonstrated a roll angle in excess of 75 degrees. Review of the crash test results suggested that a nine barrier or 112.5-ft long PCB installation would perform acceptably.

About the research

Three full-scale vehicle crash tests were conducted according to the Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL- 3) safety performance criteria on a transition between the Midwest Guardrail System (MGS) and a portable concrete barrier (PCB) system. The transition system utilized for test nos. MGSPCB-1 through MGSPCB-3 consisted of a standard MGS that overlapped a series of Fshape PCB segments that approached the MGS at a 15H:1V flare. In the overlapped portion of the barrier systems, uniquely-designed blockout holders and a specialized W-beam end shoe mounting bracket were used to connect the systems. In test no. MGSPCB-1, a 5,079-lb (2,304-kg) pickup truck impacted the barrier at 63.2 mph (101.8 km/h) and 25.3 degrees. The barrier captured and redirected the 2270P vehicle, and the vehicle decelerations were within the recommended occupant risk limits. In test no. MGSPCB-2, a 2,601-lb (1,180-kg) car impacted the barrier at 65.1 mph (104.8 km/h) and 24.0 degrees. The barrier captured and redirected the 1100C vehicle, and the vehicle decelerations were within the recommended occupant risk limits. In test no. MGSPCB-3, a 5,177-lb (2,348-kg) pickup truck impacted the barrier at 63.1 mph (101.5 km/h) and 24.6 degrees. For this test, the system was impacted in the reverse direction. The barrier captured and redirected the 2270P vehicle, and the vehicle decelerations were within the recommended occupant risk limits. Based on the results of these successful crash tests, it is believed that the transition design detailed herein represents the first MASH TL- 3 crashworthy transition between the MGS and PCBs.