Surface Material Choice, Environmental Considerations and Work Schedules for a Motorway widening project.

Justification of road choice

Highway Construction for M1 Widening

For the widening of the M1 motorway, a flexible pavement road construction will be used. The materials used in the surface course to assist with noise reduction will consist of a bituminous mixture of bitumen and pervious macadam (porous asphalt).

Flexible road construction has been selected rather than rigid for the following reasons:

Congestion, Construction & Maintenance

• Flexible pavements can be quickly constructed and maintained, where rigid pavements require frequent joint maintenance.
• They can also be maintained a lane at a time or with short-term road closures
• Therefore, flexible pavements reduce congestion during maintenance and construction

(Hunter, 1994)

Reflection

• Open graded asphalts particularly offer significant reductions in road surface glare and assist in making line markings stand out in contrast to the road.  

(Hunter, 1994)

Environmental Impact

• The bitumen used in flexible pavements does not release greenhouse gas

• The material used in flexible pavements may be reused and recycled. There is no recycling of rigid pavement, it has to be hauled off and dumped somewhere.

• When the wearing course begins deteriorate, this layer can be removed and returned to an asphalt plant and combined with new material to be used in another road project
• The production methods applied to make asphalt considerably reduce the energy used

(Garber and Hoel, (2009)

Road Safety

• Open graded asphalt provides pathways for water to run-off, minimising the amount of water between the tyre and road, increasing road safety in the wet

Noise

• Low noise asphalt surfaces can result in a reduction in noise equivalent to halving the traffic volume or reducing the traffic speed by 25%
• An overlay can be applied on an existing road surface; however, the noise absorbing properties of specially designed asphalt remain effectively undiminished over time. Hunter, N (1994)

Structural Properties

• Flexible pavement adjusts to limited differential settlement, however rigid pavements may fault at transverse joints
• Non-skid properties do not deteriorate, where rigid pavements may lose non-skid surface with time
• Tolerates a greater range of temperatures

• Easily repaired - the overlying asphalt can be easily removed and then recycled to become the new cover.
• If a rigid pavement does fail the implications are concerning. For instance, the failures take the form of rigid steps in the road grade. Each section "floats" like a boat above the sub grade and tries to level itself rather than maintain the original slope. Once the alignment gets unlocked between sections there is no repair. Sometimes 5 to 10 miles of roadway has to be completely removed.

(Garber and Hoel, (2009)

Noise Reduction

Noise reduction does not solely rely on having noise reduction materials in the wearing course. It is essential to identify the most common factor of noise generation and then give this priority.

Speed of vehicles is one of the most common factors that generate road noise. Therefore, an alternative, if possible, is to reduce the speed of traffic in urban situations to gain a considerable benefit at little cost. 

The materials used in the wearing course can also assist in reducing noise, as some materials may generate less tire noise than other surface materials. The materials used in this scheme to reduce tire-generated noise will consist of a bituminous mixture of bitumen and pervious macadam (porous asphalt). The main advantage of pervious macadam’s is a reduction in road noise when compared with a conventional bituminous or concrete running surface.  These ‘quieter’ road surfacing materials are defined as those providing a minimum noise reduction of 3.5dBA when compared to Hot Rolled Asphalt surfacing. Porous asphalt material provides a surfacing approximately 3dBA quieter than a standard Hot Rolled Asphalt surfacing, with even greater reductions in wet weather. This is a significant and perceptible reduction in noise.  (Hunter, 1994)

Sustainable urban drainage (SUDS)

SUDS is an innovative concept which includes environmental and social factors which considering the drainage of roads. When considering how the drainage system is going to be constructed it looks at quantity of runoff, and the amenity value of surface water in the urban environment (CIRIA, 2005).

Due to the research undertaken by this paper is has been decided that an SUDS systems will be used which incorporates a underground pipe system that allows water drained through a kerb which acts as a filtration system that lets water enter a pipe which then is carried away to a pond or basin.  Therefore SUDS is better suited for the drainage of the motorway rather than a conventionally designed drainage system. A justification of the choice has been given below;

• SUDS controls run-off rates and volumes of water which decreases the risk of downstream flooding.

• SUDS take into consideration the long term impact that the system will have the surrounding and aquatic environment where as conventionally designed manholes system drain water for the short term which means the quality of water may be not be assured.

• SUDS reducing pollutants concentrations with the water which protects the downstream water bodies which as the conventional methods allow pollutants to mix with the water.
• Encourages the appropriate storage of water within basins or ponds which enhances amenity and aesthetic value of developed areas whereas conventional systems are tend to flood when capacity is too large to handle.  
• The man made storage places for the water or natural storage places increase biodiversity and it provides habits for wild life which is an environmental benefit.

The reason why SUDS manage rainwater better than conventional systems is listed below;

• It deals with runoff at the source
• Its manages the potential hazards to the quality of the water at its source

Maintenance

• It important no component of SUDS is allowed to erode because erosion will reduce the systems effectiveness
• The maintenance of SUDS will be undertaken by the SUDS approving body in regards to  motorways
• Sediment entrapment facilities will be required to reduce sediment discharges
• Once SUDS is damaged it will cost more to repair compared to a conventional manhole system and weak areas such as grass will be vulnerable to cars stopping on them.

Case study

A SUDS system was utilised at Hipwood motorway service area which contributed to various drainage benefits to the service station and these same benefits can be utilised if a SUDS system is appropriately designed for motorway project. Benefits include;

• Control of water volumes to an offsite basin where as in a conventionally designed system there is chance of overflow and flooding.
• Cost of maintenance reduced compared to a conventionally design man hole system
• Robust and can withstand high winds and damage.

(Bay, R, 2003)

Planning and development

Resulting floods during 2007 the government commissioned an investigation and the Pitts report which endorsed the Flood and Water Management act. The act cover various areas such as water resources, reservoir safety, which means the SUDS system which should be incorporated for the motorway drainage, will have to comply with this act and there may be other legislation for SUDS in the future which DEFRA suggests (Roberts, 2011).