DE LOS DERECHOS Y OBLIGACIONES DEL HEREDERO

The geometric design manual is the principle source of information regarding organisational policy as it impacts on geometric design. Previously, manuals were prescriptive in the extreme and were inclined to use words such as ‘shall’, ‘will’ and ‘may not’. Little scope was allowed for the designer to apply his or her mind to the creation of innovative solutions to design problems.

The belief was that a road designed to departmental standards was safe, with the corollary that roads that didn’t match them were somehow suspect. This belief was widely supported by courts of law. Seeing that the departmental standards were derived from considerations of policy, it followed that departures from the precise scope of the standards implied that policy decisions were also suspect.

However, the winds of change have blown through the fields of geometric design and, as described in the rest of this book, have manifested themselves in fundamental changes in the approach to policy formulation. This arose, in part, from the budgetary restraints that have complicated transport departments approach to their mandate. The need for new roads and the maintenance of existing roads has not changed but the funding available to give effect to them has withered to some extent. The annual increase in budgets has largely been below the inflation rate, implying a net decrease in available funding.

The standard political demand has been for departments to ‘do more with less’. This they have achieved largely through changes in their approach to policy formulation that have kept pace with changes in the philosophy of design. For example, it was noted that there were stretches of road that may, in fact, not have been upgraded to match the most recent design standards but, in spite of this, had good safety records. This led directly to the development of the concept of the design domain as discussed in Chapter 4. This became necessary because, in rehabilitation exercises, shrinking funds meant that authorities had a choice between rehabilitating a road from end to end or allocating some of the available funding to the upgrading of the geometry of a horizontal or vertical curve, leaving a portion of the pavement unrehabilitated.

The simplistic approach of the law courts regarding the correlation between standards and safety has been replaced by the mechanism referred to as the design variance whereby the road authorities can prove that they have applied their minds to the standards in use on their road networks. The ruling of a South African judge several years ago that ‘bridges must be designed to withstand the worst flood of all times’ would receive short shrift today.

2.6.1 Cost-efficient design

Previous polices were directed towards geometric design that minimised the cost of con- struction. It took some time for departments to realise that, in minimising the cost of con- struction, the resulting light pavements tended to deteriorate rapidly, imposing a significant maintenance bill on them. The policy was then adapted to minimising the cost of construc- tion AND maintenance. With transport economics gaining ground, the realisation finally dawned that construction and maintenance between them added up to about 25 per cent of the total cost of a road, with road user costs being the remaining 75 per cent. The current

24 Geometric design of roads handbook

approach is that the ‘whole life’ cost of the road most be minimised to achieve a cost-effective design. The so far unproven belief that ‘for every metre of false rise and fall eliminated, the length of the road can be increased by 25 metres’ arises from this new approach.

As illustrated in Chapter 16, while economic analysis is an indicator of cost efficiency, it is necessary also to consider the irreducible factors, that is, elements to which it is not possible to attach a cash value. These include the issues of social factors and minimisation of the environmental impact of the road.

Although it doesn’t have the formality of a policy with a proper rationale, the design life of a road is often taken as being 20 years. The annual maintenance and road user costs of this period are discounted to the baseline year, which normally is the year in which the road either has or will be opened to traffic. This provides a net present worth of the whole life cost of the road. It is recommended a policy be formulated whereby a range of design lives is analysed in terms of annual maintenance and road user costs with a view to establishing the optimum design life in terms of the minimum present-day discounted costs.

2.6.2 access control

As discussed in the following chapter, access control deliberately restricts access to any road to ensure that its functionality is not compromised by the number of vehicles on it. This can be achieved, for example, by

• The systematic spacing of successive intersections • The layout of intersections

• The design and operation of driveways, intersections and/or interchanges • The design of median openings

In rural areas, access to a road is usually limited to one access per farm, with a farm defined as comprising all those properties that have been consolidated into and operated as a single unit. In urban areas, successive intersections are sometimes located to promote ‘green wave’ operation. This means that, just as a platoon of vehicles reaches an intersection, its traffic signal changes to showing a green phase. In very special circumstances, it is even possible to have green wave operation simultaneously in both directions. The norm is that signal phasing is set to favour the heavier flow, for example, the peak hour flow toward the CBD in the morning peak and away from the CBD in the evening peak. The opposing flow in either case simply has to take its chances with a less than optimal signal phasing.

Developers of areas immediately adjacent to a freeway often have the belief that direct access to the freeway is absolutely essential for the viability of their parcel of land. This may be true but it is not always possible to grant the requested access without jeopardising the operation of the freeway. Rejection of the application for access is invariably followed by recourse to a court of law with a view to overturning the departmental ruling. Arguments are offered in favour of the massive job creation that will follow the approval of the applica- tion, improvement in the tax base of the department concerned, improvement in the general economy of the area and so on.

The problem may be that there simply isn’t enough space between existing interchanges to accommodate the interchange needed to provide the requested access. There has to be adequate space between on upstream on-ramp and the following off-ramp to allow for the weaving that has to take place between merging and diverging vehicles. Without this, freeways simply become totally clogged and brought to a standstill. All the rosy visions of the developer are then brought to nought by what used to be an operating freeway being brought to the status of an expensive car park.

Policy 25

In general, courts seem to favour the case of the plaintiff, that is, the developer. The devel- oper is seemingly not required to substantiate any of the claims, fanciful or otherwise, made in respect of the advantages of providing the development. The Transportation Department, on the other hand, is placed in the position of having to prove the merits of its rejection, to prove in fact that ‘it has applied its mind’ in deciding not to approve the application.

In cases where a development may be granted access to a freeway, the department invari- ably would not have the funding available to finance the required interchange. If the devel- oper is not prepared to carry this cost, the interchange would simply not be provided. It should be noted that, while weaving within interchanges can be accommodated by collector– distributor roads, weaving between successive interchanges is far more critical to the opera- tion of the freeway as a whole. This is because it involves the operation of the main line carriageways as opposed to interchange ramps. If there is any limitation on the space needed for provision of the interchange it may thus be necessary to provide auxiliary lanes upstream and downstream of the site to facilitate these weaving operations.

2.7 CONCLUSION

The most appropriate policy for transportation departments to adopt is to accept that the rigidity of geometric ‘standards’ is no longer and, in fact, never was a basis for good design. The fact of the matter is that the ‘one size fits all’ approach to design is fundamentally flawed. A standard appropriate to the southern border of Texas is quite possibly not going to be appropriate to Alaska.

Designers have to be allowed the flexibility that the politicians were inadvertently asking for with their need for ‘appropriate standards’.

As advocated throughout this book, a philosophy and policy of rigid ‘design standards’ should be replaced by design made possible by ‘geometric guidelines’. Obviously, this is not advocating a ‘laissez aller’ approach to design that is but a short step away from anarchy. Departing from a design value recommended by a guideline would have to be motivated by the designer and formally approved by the Transportation Authority before it could be incorporated in the design of a road.

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Chapter 3