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It is inevitable, the carrying out of roadwork operations creates a certain nuisance on traffic, customers and local residents. By playing on good factors it is possible to reduce these nuisances. However, a good understanding of them is necessary (CCR, 2009). The disturbances created by work activity can be found in different ways: noise pollution, visual pollution, congestion, insecurity feeling, loss of time, loss of moneyâ€¦ In some cases, it is possible to quantify the nuisance and in other cases it is more difficult. For example, an increase in trip lengths or congestion factors caused by a road construction work can be measured whereas people feelings and visual pollution are hard to quantify (SETRA, 2002).
During the construction process, it is essential to find a good compromise between the comfort of the public and efficiency of work. Then, a key factor to take into consideration is the satisfaction of motorists and their points of view toward worksites. A large occurrence of works in a same area as well as a large increases of trip durations can irritate some motorists. The image of road construction and worksites in general can be damaged by a bad traffic management alongside a construction work (Peyronne, 2000).
Whatever a user is travelling by car, bicycle, public transportation or just walking, he has to face more or less worksites nuisances. Most of the time, users wonder if the duration, the method used or simply the moment when a work is carried out are adequate (CCR, 2009). A good communication about the nature and duration of the work is necessary to improve the motorists perception of worksite and increase their knowledge of what happens in the work area which could lead them to adapt their behaviour to the situation (Dargent, 2000).
Enhancement and maintenance operations of main networks often require temporary traffic management measures to deliver safe road works, temporary closure or incident management (Department for Transport, 2009).
In order to keep road users or road workers safe and maintain a high level of traffic fluency, it is necessary to inform and to guide motorists, and to convince them of modifying their behaviour and adapt it to the unusual situation (SETRA, 2002).
In order to face the conflict between work activity and traffic flow, work strategy have to be prepared. On large linear projects, the success of the construction process depends extensively on planning and controlling the work to accommodate both uninterrupted traffic and work efficiency. Managers have to provide an efficient alternate bypass or a suitable traffic closure to synchronise traffic flow with work activities and prevent idle time for labour and equipment (Sharma, McIntyre, Gao, & Nguyen, 2009). They need to study traffic flow around the work zone in order to determine what strategy fits the best with the constraints and figure out if lane closures are possible (Germy, 2000). Those strategies are part of a Transport Management Plan (TMP) elaborated during the design which aims to carry traffic through or around the work zone using other existing infrastructure or temporary traffic control methods (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007). Linear projects like motorways or main trunk roads are often quite lengthy and construction cannot be realized with traffic disruptions on the entire length of the project at the same time. Interventions have to be split into several workzones to reduce the length of necessary lane closures or diversions and then reduce traffic disturbances. The segment division would also permit a better management of resources (Sharma, McIntyre, Gao, & Nguyen, 2009). Every project is different from another. A strategy has to be adapted to the project which is considerate (??). Examples of strategies successfully used in road construction projects (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007):
Alternating one-way operation,
Detour or diversion,
Full road closure or intermittent closure,
Lane closure or lane constriction,
Use of shoulder.
This list is extensive and choices can be combined to fit perfectly with the situation. The most common in road maintenance and enhancement remains the lane closure. However, several safety issues result from this strategy. Congestion cause by this closure can result in potential rear-end accidents or other kinds due to drivers' behaviour. Indeed, motorists can be distracted by a construction site or frustrated by congestion or by not knowing on which lane to drive (Petsi, Jessen, Byrd, & McCoy, 1999). Work strategies have to be chosen wisely as they cost time and money to the contractors but also to the motorists (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007). The decision making on the strategy to adopt should be based on work efficiency, on traffic fluency as well as on safety.
Work zones in road construction and maintenance represent hazardous places for workers and motorists mainly because of the presence of traffic (Bryden & Andrew, 1999). Recurrent accidents reported in these kinds of projects are collisions between two vehicles caused by distracted drivers, vehicles following trucks or cars accessing the site, workers struck by vehicles or drivers trying to manoeuvre around a closure because of lack of patience (Ullman, Finley, Bryden, Srinivasan, & Council, 2008). Several factors of risk can be identified such as operative speed, visibility, driver's behaviour or work zone information. Most of these factors are connected. Indeed, sight distance and speed influence visibility, and knowledge of the work activity, speed and visibility influence driver's appreciation of the danger and thus influence his behaviour (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007). Then, several safety systems had been developed to increase the level of safety in a work zone such as (Layerle & Anzoras, 2003):
Physical separation between motorists and worksite
Efficient information systems ahead of the work zone
Adapted temporary signing
On-call patrols to limit the duration of car assistance around the work zone and prevent congestion
Access zones delimited and safe
Safe areas laid out for drivers every 2km for long linear projects
Real time information regularly along the work zone
An adapted risk assessment and an efficient planning of work can limit most of the risks generated by the traffic around a work zone. Particular safety systems as well as a good information to road users are the key of safety implementation around an infrastructure worksite.
Road enhancement and maintenance worksites are located along motorways, trunk roads or local roads. Whatever is the size of the work, it always results in traffic disturbance. The presence of work zones on the network has an impact on traffic and may become a location for car crashes. This problem is known by all transportation agencies which have to set up complex planning of work zone operations (Racha, Chowdhury, Sarasua, & Ma, 2008). This impact generated by work activity may embrace several forms: congestion, disruption of commercial and industrial activity, safety issues, change in local driving routine or citizen complaints to quote only few of them (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007). To avoid or at least reduce those disturbance, managers have to maintain a maximum traffic fluency and limit the nuisances caused to motorists and road users in general. They will limit the duration of work and use only the necessary area to work according good safety considerations (Vidal, 2000). The conflict between the workzone and traffic flow requires them to think about adequate strategies in the early preparation of the project.
To summarise, a safe and efficient traffic management is base on the following fundamentals (Department for Transport, 2009):
Provide a clear and early warning of obstructions in the road
Optimise road space and provide a reliable safety zone and working space at site locations
Give correct and adequate directions to road users in order to help them in their decisions
Minimise potential conflicts between road users
Minimise potential conflicts between road users and road workers
Provide credible temporary traffic signs
Restrict speed around
Work at night
In order to limit the impact of construction on traffic flow, many companies working on high-volume facilities decide to adopt night work strategy (Ullman, Finley, Bryden, Srinivasan, & Council, 2008). At night, traffic volumes are generally lower than volumes during daytime, thus working at night permits to reduce the disruptions and seems more adapted for projects that imply heavy traffic (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007). However, night work implies several non-negligible issues (Goyet, Salin, & Spillemaecker, 1999). Indeed, because of reduces visibility and increased driving speeds at night, safety requires more investment from managers (Ullman, Finley, Bryden, Srinivasan, & Council, 2008). Quality is also a recurrent issue because the lack of 3D vision has an impact on the perception of distances and landscapes. Finally, operating costs are higher due to unusual working conditions. The number of workers and supervisors has to be increased and lightning has a cost (Goyet, Salin, & Spillemaecker, 1999).
Several constraints in time and location appear. Work at night can be efficiently used on main road infrastructures where traffic flow does not allow working on the daytime. But in an urban or semi-urban context, night work in a mixed or residential area is not conceivable because of nuisances produced (Caignie, 1999).
In order to get a better overview to the situation, advantages and disadvantages of work at night can be drawn side by side in a table (Mahoney, Porter, Taylor, Kulakowski, & Ullman, 2007):
Traffic volumes low
Workzones have low impacts to traffic flow
Workzones have low impacts to commercial activity
Better work efficiency
Higher operative costs
Higher safety risks (speed, somnolenceâ€¦)
Social impacts to work fore
Reduced visibility (potential impact to quality)