49106 Road Engineering Practice

Explain how you would decide on the appropriate width of a shoulder for a rural road. In your answer cover the critical issues and discuss the benefits of bitumen sealing of that shoulder.Explain how large heavy vehicles such as B Doubles and semi-trailers affect road design in urban areas

When designing a rural road connecting two major towns, what design and checking vehicles would you use In your answer provide a brief explanation.Constructability is an important feature of a good road design. What are the major constructability issues you would consider in the design of a road in an urban area.What do you understand by the term “safe system approach to road design.

Horizontal curve design

L = (wN)e_d)/G x b_w

L = (7 x 4).03/-1 x 

 Ssd = (pi. X R_v)/90 x {cos^-1(R_v - M_ssd/ R_v}

1182 (1- cos (220 x 400/pi x 1182)

=2.17 m

The shoulder widening is not required and the clearance as well since the ssd is enough for the viewing.In the rural design, the traffic using the road will be key in the determination of the shoulders of the road. The overtaking positions will be determined and the traffic will help to determine the width of the shoulder. For a heavy traffic sections and roads. Wider shoulders will be provided on the design to ensure that the shoulders can be passable. In addition, the foundation of the shoulders will be designed to meet the same characteristics of the main lanes. This is because the shoulders will be at times used at times the traffic is heavy. This will ensure that the road is able to meet the design periods. The shoulders of the roads will be key in ensuring that the flow of traffic is maintained at its peak and flow is ensured. In addition, the shoulders is likely to change as the traffic changes at different parts of the rural area. The traffic count will be used to determine the width of the shoulders at the different positions.

The heavy vehicles have high axle loadings and this is able to affect the asphalt by exerting the pressure on the asphalt. The pressure is able to affect the loading characteristic per unit area on the road section. The axle loading is the key factor which is able to affect the road design at the urban roads. The big vehicles have high number of axle loading and therefore exert more pressure per unit area of road in a given moment.

When designing a rural road connecting two towns, the load of the vehicle is a key check which is required. This will ensure that the road is designed to meet different design period which can only be attained with proper consideration of the road section. The checking for the loading will ensure that the vehicles on the roads are not able to exceed the required weight and load design of the roads.

One of the key construction issues to be considered for a good road during the design is the shoulder structure. According to different reports and researches, widening the right pavement lane and placing the edge stripe 0.5 m from the outside pavement edge helps to improve the asphalt and concrete pavement performance. In addition, the shoulders should be able to withstand the wheel loading at any given moment. In this case the design of the shoulder should be able be of the same design as the mainline to enhance the wheel loading. Foundation is another key structural area which is key for the road design.

The foundation has to meet key specification such as being uniform, stiff, moisture and frost resistant. The uniformity of the subgrade and its stiffness must be maintained. The design has to be made on all the layer and ensuring that the specific characteristics are met. The NHS and SHAs regulations must be observes during the designs of the road and the foundation designs of the pavements. Characteristics such as free to drain and resistant to moisture which is related to damage must be observed during the design of the base courses. In addition, the traffic is another key factor which need to be considered during the design of the roads.

The designers have to collect the traffic data from SHA to enhance the proper use of the roads and ensuring that they meet their requites lifetime. The axle loads of the traffic has to be maintained and ensure that the roads meet their design life. Economic analysis is another key factor which need to be considered during the design period. The economic factors ensures that the value for money for the pavement is met. Alternative methods must be provided for the materials to ensure that quality and value for money is achieved during the design. The economic values provides the different options for carrying out the design and ensuring that it meets the required standards.

The “safe system approach” is a system which is able to focus on designers as the key people who will enhance the safety of the roads than the users of the roads. It is able to in cooperate the different elements such as the roads and roadside, travel speeds, vehicles and road users. The designers is able to cater inclusive of all the factors which include the elements of the drivers, motorcyclists, passengers, pedestrians, cyclists and drivers of the special vehicles. The safer system approach uses inputs such as data, research and evaluation of crashes and risks.

The safety factors in this approach is looked and addressed at the design stage and therefore able to help and focus on elimination of crashes and death at this level. In addition, the system is able to include three key aspects which include the education and information support for the road users, post crash emergency care and education and enforcement of road rules. At the end of the approach, the safer travel is admitted at the end of the process. In addition, it includes the design elements such as the safe road and roadsides, safe speeds, safe vehicles and safe road users. The safe system approach is therefore able to consider all the safety of the different users of the road.

A dense graded asphalt is a mixture which is intended for the general use. The major characteristic is that the mixture is usually impermeable. According to their sizes, the dense graded is known to have the nominal maximum aggregate size. The type of asphalt is able to offer characteristics which are key in pavements. The type of asphalt work well in structural, friction, levelling, and patching needs which are common in pavements. On the other hand, the fine gap graded  asphalt is able to consist finer materials and sand sizes. Moreover, the FGGA is a further classification of the dense graded asphalt where the sizes of the aggregate is changed to finer details.

One of the major disadvantage for the dense graded asphalt is that it cannot accommodate high asphalt content without becoming unstable and leading to rutting. The low level of the asphalt make them more common to cracking and more permeable. In addition, the coarsening of the mix leads to a more drier mix which is difficult to compact and become more permeable. In addition, the mix is not designed to have stone contacts. This is able to affect their strength and durability. In addition, the FGGA is able to consist of finer element and is not designed to make contacts with stones. This is able to affect their use and affect their durability a lot. This is one of the key con of the FGGA which is able to high affect its use and durability.

Asphalt is a composite material which is used for different purposes in pavement design and construction of roads. One of the key component in the asphalt if the binder. The main purpose of the binders is to bid the different components and materials in the asphalts. In the real essence, the bidders are able to compact the materials together and help them to keep them at one position after compact. The binder is an essential element which helps to keep the pavements in one position and increase the performance of the asphalt. After compact, the asphalt is required to be intact and this is usually achieved with proper binder which helps to keep the different components in one place. In addition, the binder is able to keep and maintained the required temperatures of the asphalt.

The binder also help to harden the mix of asphalt to the required hardness. Another key component of the asphalt is the aggregate. The aggregates are key component which is used to achieve the required characteristics which are key for the different purposes. The roughness characteristic of the asphalt is achieved through the use of graded aggregates. Another component is the fine aggregates in the asphalt. The fine aggregates are used to fill the gaps and ensure that the asphalt is water tight and impermeable. This is one of the key characteristic which the asphalt is required to meet and therefore the fine aggregates is required and key for the asphalt performance.

References

Asphalt Construction Handbook. 6th ed. Barber-Greene, A Division of Caterpillar Paving Products Inc., 1992.

Planche, Jean-Pascal, Helen W. King, and Gayle N. King. "A Refiner's Approach to Asphalt Characterization." Nature, April 18, 1991, pp. 24-25.