The aging of road infrastructure, coupled with an increase in traffic volumes, has taken a toll on the existing road network.
The need for maintenance and rehabilitation operations on roadways is ever increasing. While traffic-control techniques for road construction and maintenance vary widely, one of the methods experiencing increased use, because of its ability to improve efficiency and minimize operational impacts, is mobile lane closures.
This article summarizes work undertaken for an NCHRP project 20-5 that examined practices employed by transportation agencies during mobile lane closures. It includes a summary of a literature review that looked at the state of the practice in regards to mobile lane closure and describes the findings of a survey questionnaire that examined practices employed by various U.S. and Canadian transportation agencies. Findings from the study also are summarized.
A mobile lane or shoulder closure in this study is defined as any activity associated with short-duration work that moves continuously or intermittently along a road segment. Some agencies call this type of closure a mobile operation. The work might be done directly from the moving vehicle or equipment or it may involve workers on foot.
Why mobile lane closures?
Whenever there is construction or maintenance work being done on the roadway, not only does it affect traffic flow, but also it has the potential to reduce the safety of the roadway for both road users and workers. Data show that more than 1,000 fatalities and 40,000 injury crashes per year in the U.S. are related to work-zone crashes.
Mobile lane closures are common temporary traffic-control measures and are used for many short-duration construction, maintenance and engineering activities performed on roads open to traffic. As opposed to stationary, longer-duration road closures, mobile lane closures employ a traffic-control setup that moves with the work and does not channel and separate moving traffic away from work crews through the use of physical barriers, such as temporary concrete barrier, delineators, etc.
The goal of employing mobile lane closures is to improve the safety of workers involved in road work and road users who pass by work areas while at the same time minimizing overall delay and disruption that may be caused by employment of longer-duration road-closure techniques.
Typically the procedure is best applied in situations where the work being undertaken is of a very short duration or is in fact physically moving along the road. Examples of work for which moving lane closures may be used include, but are not limited to, the following:
- Pothole patching;
- Line painting;
- Installing raised pavement markings;
- Vegetation spraying;
- Storm-water catch basin cleaning; and
- Installation and removal of static work-zone traffic controls.
The results of the literature review indicate that, in the U.S., numerous states rely on regulations, policies, standards or documented practices which are either complementary or supplementary to the Manual of Uniform Traffic Control Devices (MUTCD), as published by the Federal Highway Administration (FHWA) of the U.S. Department of Transportation (U.S. DOT). In Canada, each provincial agency complements or supplements the Canadian MUTCD, as published by the Transportation Association of Canada (TAC), with its own published requirements.
Not surprisingly, there is some disparity and overlap between the definitions and interpretations relating to mobile lane closures between jurisdictions. While there are differences, there are a number of successful mobile lane closure traffic-control devices and techniques currently being used by transportation agencies to ensure the safety of workers and motorists. Details of current mobile lane closure techniques defined in MUTCD documents are not repeated in this article but should be referenced for an understanding of the standard techniques that are in use.
The literature review specifically looked for innovative and even experimental devices and technologies that were being employed in mobile lane closures. Various state DOT and other national research programs were found to be regularly looking for or developing innovative technologies that will improve the safety of mobile lane closures. A number of safety-device concepts were identified by the Strategic Highway Research Program (SHRP) to be applicable in work-zone maintenance activities.
The following devices were identified in the review.
- Vehicle intrusion alarms provide safety to the workers by alerting them either by audio or visual means that a driver has entered the work zone. The alarms can provide sufficient warning for the workers to clear out of the vehicle’s path;
- Flashing stop/slow paddles are similar to the conventional stop/slow paddles used by flaggers at work zones, but are equipped with high-intensity flashing lights that are visible even during the day. When a driver fails to heed the flagger’s instructions, the flagger can activate the flashing lights to get the driver’s attention;
- A portable-crash-cushion trailer is a tilt-bed trailer equipped with a pallet of hinged steel plates. Sand-filled barrels are secured to the pallet, and a winch is provided to assist in the installation and removal of the barrels;
- Remotely driven vehicles are large dump trucks that are supposed to follow workers as they move along the highway, serving as moving barriers between work crews and oncoming vehicles. The shadow vehicles lessen the risk for highway workers but put the driver of the vehicle in a dangerous position should the vehicle be hit;
- Automatic cone-setting devices can automatically place and retrieve cones in the work area, replacing the need for workers to do that job, which can be difficult and hazardous in mobile lane closures;
- Automated pavement crack sealers of two types were developed: a longitudinal crack sealer and a random crack sealer. They increase worker safety by removing the need for workers to hand-seal pavement cracks; and
- Debris removal vehicles of two types were developed: an automated litter bag/debris collector vehicle and a debris vacuum system. These devices can greatly improve the safety of workers by keeping the workers inside the vehicle, thus decreasing exposure to moving traffic.
These devices have been evaluated on their functionality in mobile lane closures and short-duration operations based on the following five criteria:
- Reduce exposure of workers to vehicle;
- Warn motorists/crew to minimize likelihood of crash;
- Minimize the severity of crashes once they occur;
- Provide separation between work crew and traffic; and
- Improve work-zone visibility/presence.
The research concluded that none of these innovative or experimental devices fully satisfy all the criteria, though some show significant promise toward improving the safety of mobile lane closures. Of greatest promise are remotely driven vehicles. These devices were found to at least partially satisfy all of the criteria. Unfortunately, the literature review also concluded that remotely driven vehicles are still very much in the experimental stage and are not commercially available for wide-scale deployment.
In order to assess the state of the practice among transportation agencies with respect to mobile lane closures, a survey was e-mailed to DOTs in each of the 50 states in the U.S. as well as the District of Columbia and Puerto Rico, along with seven provinces in Canada. The purpose of this survey was to identify notable practices employed by transportation agencies during mobile lane closures under various road and traffic conditions. The range of technologies in use, challenges faced and solutions to problems found also were investigated. The survey also assessed the perceived effectiveness of the identified practices and the motivations behind their use from the agencies’ prospective.
The survey consisted of 74 questions designed to gather information on regulatory and guiding documents, practices, equipment used, field experiences and technology and research needs. The survey was sent to both the maintenance and the traffic engineering departments of each state and provincial DOT. A 56% response rate was achieved.
The survey results revealed the following:
- Wide variations exist in the types of temporary-traffic-control (TTC) operations used by the respondents for different activities, which they included in their descriptions of mobile lane closures;
- The majority of the respondents used internal guidance documents to ensure proper selection and applications of their TTC for a mobile lane closure;
- For the majority of respondents (61%), truck-mounted attenuators (TMAs) are mandatory on shadow vehicles in mobile lane closures;
- Most of the participating DOTs in the survey do not use signs mounted on the first shadow vehicle to indicate the number of vehicles in a work convoy;
- Over 64% of the responding DOTs do not use equipment to reduce exposure of workers or completely eliminate workers on foot in the mobile lane closure work zones, such as automatic crack sealing, patching, debris collection vehicles, etc.;
- Almost no agencies are regularly using work-zone vehicle intrusion alarms;
- Flaggers continue to be used by 62% of respondents for mobile lane closure work zones on two-lane roads;
- In terms of the use of signs, most participating DOTs continue to use temporary signs installed in advance to warn motorists about a mobile lane closure; and
- Only 20% of the respondents were aware of any technology/device developments or research projects in progress that could increase the safety of mobile lane closures.
The following are some of the aspects of mobile lane closures that respondents thought should be further researched or addressed to increase safety:
- Motorist education and awareness;
- Improvement of safety devices for workers;
- Improvement of traffic protection standards for the workers;
- Workers’ visibility;
- Glare at night from a nonproject source;
- More advance warning on high-speed roadways;
- Vehicle-mounted equipment that can be deployed to warn motorists that a shadow vehicle is stopped or moving slowly;
- Effectiveness of static signs mounted on the back of work, sign and shadow vehicles;
- Safety of mobile lane closure using limited resources, equipment and people;
- Research on human response to mobile lane closures or spot hazard; Mobile flagging; and
- Use of portable changeable message signs versus arrow panels only in mobile lane closures.
Mobile lane closures are used frequently in North America in roadway maintenance and rehabilitation operations. However, when and how this type of operation is carried out may vary significantly. In addition, while both the U.S. and Canada have their own MUTCD, which address some procedures for temporary traffic controls that can be applied in mobile lane closures, there are no clearly standardized practices for mobile lane closures that are uniformly applied.
While extensive research has been done on the different aspects of mobile lane closures, such as the effectiveness of specific traffic-control devices in such operations, there are still a number of other issues upon which research information is either limited or unavailable.
There were gaps found while conducting the literature review: notably, specific data on mobile lane closure work-zone crashes are generally not available; a lack of research in regards to the training of workers performing mobile lane closure; and a lack of research on appropriate vehicle spacing (buffer vehicles and work vehicles) and optimal location of workers within the mobile lane closure work area.
There also is the potential for improved safety in mobile lane closures through the broader application of innovative technologies. These tools show promise for expanded application but appear to be in limited use.