Question

. Discuss the potential short term and longer term impacts of introducing a road bridge link to the Isle of Wight with reference to each of the four stages of the four stage transport model and on carbon emissions

Answer 1

potential short term and longer term impacts of introducing a road bridge link to the Isle of Wight

The Isle of Wight is situated between the Solent and the English Channel, is roughly rhomboid in shape, and covers an area of 150 sq mi (380 km2). Slightly more than half, mainly in the west, is designated as the Isle of Wight Area of Outstanding Natural Beauty. The island has 100 sq mi (258 km2) of farmland, 20 sq mi (52 km2) of developed areas, and 57 miles (92 km) of coastline. Its landscapes are diverse, leading to its oft-quoted description as "England in miniature". In June 2019 the whole island was designated a UNESCO Biosphere Reserve, recognising the sustainable relationships between its residents and the local environment.

The four stages (or four steps) transportation/land use model follows a sequential procedure:

• Trip Generation. For each discrete spatial unit, it is estimated the extent to which it is an origin and destination for movements. The output is usually the number of trips generated and attracted by a given spatial unit.
• Trip Distribution. Commonly a spatial interaction model estimates movements (flows) between origins and destinations and which can consider constraints such as distance. The output is a flow matrix between spatial units.
• Modal Split. Movements between origins and destination are then disaggregated by modes. This function depends on the availability of each mode, their respective costs, and also social preferences.
• Traffic Assignment. All the estimated trips by origin, destination and mode and then “loaded” on the transportation network, mainly with the consideration that users want to minimize their travel time or have to flow through existing transit networks. If the traffic exceeds the capacity of specific transport segments (which is often the case), congestion occurs and negatively affects travel time. This in turn, through a feedback process, may influence trip generation and distribution.

This procedure is consequently iterative and converges towards a solution, often measured as the minimal transportation cost considering a given travel demand and the characteristics of the existing transportation network. It relies on an extensive array of data that can be obtained through census information, surveys and estimates.

SHORT TERM AND LONGER TERM IMPACTS OF INTRODUCTION OF A ROAD BRIDGE

Effect of Environmental Conditions on Foundations for Bridges

Environmental factors that affect the selection of over water foundation types and their construction methods are discussed below:

Effect of Sea or River Current on Bridge Foundation

Piles or piers may be subjected to drag force which is generated by sea or river current. This force creates scour holes in locations where the soil is vulnerable to erosion at sea bed level.

The presence of these holes around cofferdams are undesired since it generates circular movement of water in this location because of temporary conditions such as partially driven sheet piles.

Current drag force is likely to create issues while sheet piles or bearing piles are installed. This is because such force at high velocities oscillates and consequently damages the pile prior to placement of pile caps or temporary grit provision which prevents the pile oscillations.

Effect of Ship Collision on Bridge Foundation

Collisions are likely to occur due to ships, which are out of control and possibly cause bridge pier failure. In specific broad estuaries, deep water channel may swing from one side to another in a considerably short time and almost all piers of the constructed bridge would be at risk.

Effects of Floating Ice on Bridge Foundations

There is a similarity between the effect of floating ice sheet impact and collision ship influence on the bridge pier. So, their design is also similar to each other. However, there is an extra danger in the former case which is the gradual increase of pressure due to the amassing of ice packs.The direction of build up pressure is transvers to the bridge pier or vertical when pressure ridges start to form. It is recommended to use single pier bridge rather than group piles because single piles will alter the direction of ice floes and prevent ridge pressure formation. For gravity base structure, the best form of bridge foundation in areas subjected to floating ice is the application of slender piers with a massive base. This is because the latter would provide resistance against sliding and overturning forces whereas the former does not create much resistance against floating ice sheet force. Moreover, if the utilization of piles are needed due to ground conditions, then a ring of closely spaced skirt piles should be installed around the group pile.

Finally, for the case the movement of water is parallel to the river bank, the introduction of cut waters to the piles would provide satisfactory answer to the floating ice forces. This is because cutwaters would cut and break ice floes and consequently avoid the impact and pressure of floating ice sheets.

Effect of Earthquakes on Bridge Foundations

Earthquakes impose devastation force on the bridge piers especially in deep water because the force exerted on the bridge superstructure would be combined with the load on the pier and consequently substantial overturning moment at the base of the pier will be produced. The mass of water replaced by pier is specified to be added to the mass of the pier. The eccentric load supported by the pier is crucially large in deep water which makes the selection of slender pier and massive base a desirable option. It is recommended to use circular column because seismic forces do not have particular direction and it can be in any direction. Another problem is the liquefaction of loose to medium dense soil due to ground shaking. This issue may be tackled by using pile foundation to densify the soil to an extent that can support piers safely. The depth of liquefaction may be computed using particle size distribution and in situ density. Finally, liquefaction may cause tsunami or develop submarine flow slides and subsequently a horizontal force at the base of the pier will be generated.

Environmental Effects of Emissions of CO2

Governments and international organizations have been taking actions to protect the quality of air, as well as In more recent years to control emissions of climate forcing agents. Ambient air quality standards and guidelines, issued by environmental protection authorities, are instrumental in achieving the air quality objective. An example of such legislation is set by the US National Ambient Air Quality Standards (NAAQS) adopted by the Environmental Protection Agency (EPA). The NAAQS apply to both human health (primary standard) and public welfare (secondary standard). Primary standards protect sensitive members of the human population from adverse health effects of criteria air pollutants. Secondary standards protect the public welfare from any known or anticipated adverse effects associated with the presence of a pollutant in the ambient air. Welfare effects include effects on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, visibility, climate, damage to and deterioration of property, hazards to transportation, as well as effects on economic values and personal comfort and well-being.

Under the US Clean Air Act of 1990, the NAAQS standards set maximum ambient concentration limits for six criteria pollutants including:

1. Ozone, O3
2. Carbon monoxide, CO
3. Nitrogen dioxide, NO2
4. Lead, Pb
5. Particulate matter below 10 µm, PM10
6. Oxides of sulfur, SOx

This have consequences on the wildlife and plants.

• For birds and mammals : the carbon can kill by asphyxiation at a certain level and time of exposition. Its chemical property, higher than oxygen, permits it to be able to rapidly cross numerous types of biological membrane (including central nervous system).
• In the oceans : the circulation of oceans is also affected by human carbon emissions. It makes oceans more acid. Thus, numerous fish can wind up to the poles, where the water temperature change less rapidly. Regarding ocean current, they could slow down, or even stop. The CO2 absorbed could be released and worsen climate change.
• For the plants: with a low dose, the CO2 can permit growth of so many vegetal species. After experiences, this has been proven, but until a certain level. When this level is overpassed, the growth of vegetal stabilize or reduce. It’s for the moment difficult to see what is the exact level that stop this growth as it can change in function of the plant species. But we talk about environmental acidification.

The Positive Economic Impacts of Bridges

In recent years, economists have recognized three key things bridges do that propel economic activity.

#1 – Bridges are a critical component of a nation’s infrastructure, making it possible to ship raw materials and finished goods to factories, warehouses, suppliers, distributors, stores, and end-consumers. Bridges also facilitate travel so consumers can purchase goods and services in their own communities and beyond. When a bridge closes, economic activity slows or grinds to a complete halt.

#2 – Wages earned by bridge construction and maintenance workers have a positive economic impact when used to buy things at local businesses. An investment in wages, and the related consumer spending that results from it, is proven to pay off many times over.

#3 – Bridges increase cash flow when they join two places that complement each other economically. It can have a powerful impact when an area that has a large money supply is connected to one that has goods or services to sell or people who need work. The same is true when a community that has raw materials gains easy access to another that has factories able to convert them into salable goods.