Civil Engineering September 2022 | Vol 30 No 8

22 September 2022 Civil Engineering In assessment reports, the “big picture” assessment is generally missing. The road section comprising the project would be a part of a much longer route. What is the primary function of the route? What are the local conditions and land uses that the road passes through? Does the project portion of the route pass through rural areas, urban areas, or both? This information, while only requiring a paragraph or two, informs the functional classification of the route, which is a design’s starting point. “While geometric features are not criteria for defining a functional classification system the opposite can be true. The functional classification system must guide road geometry and design standards.” – TRH26 Chapter 3.10 (COTO, 2018). A road may pass through different land use types and change from rural to urban. While this should not change the functional classification of the route, some geometric standards can change. The point is that few projects are a “one design fits all”. Environments change, topography changes, traffic volumes change, and there may be high pedestrian and public transport needs. These need to be identified and where necessary catered for going forward. The key output from the assessment stage is a strategic approach to developing appropriate designs, confirming what the objectives are and what functionality needs to be provided to meet the needs of all the users, including where and how these may change, as well as identifying what additional information is required through detailed studies, necessary for the development of the design concepts. DETAILED STUDIES Additional information may be needed to develop the designs and may entail data collection (surveys) and the analysis of the survey data to produce input parameters for the designs. The detailed studies are carried out to do this. One of the detailed studies is the determination of the loading that the infrastructure must carry. I assume that this is a critical requirement for the designs in most civil engineering projects. On road projects, this unfortunately does not appear to be the case. So long as there is a traffic count somewhere, and a growth rate out of a manual, we have a forecast. Using these forecasts, the traffic engineers and the geometric designers can go to town designing some incredible infrastructure. The problem is, if the forecast is wrong, so are the incredible infrastructure designs. Issues related to incorrect forecasts is a topic for another article. Suffice to say, the determination of the traffic loading for road design must be given due consideration. The traffic loading, as determined at this stage of the design, must be carried through to all other aspects of the design. However, in addition to the derived traffic volumes and growth rates, the traffic en- gineers, in conjunction with the geometric and pavement designers, consider the fac- tors that could influence the growth rates. With this, the sensitivity parameters (plus or minus) to derived growth rates should be determined. CONCEPT DESIGNS Using the output from the assessment and the detailed studies, the strategic direc- tion defined (functional classification) should be re-assessed or confirmed. With this and the necessary information (traffic loading and existing infrastructure condi- tion), appropriate alternative concepts can be developed. These should be done to sufficient detail to ensure that the project is technically feasible and can be priced to an appropriate level of accuracy to enable the economic assessment of the alterna- tives. There needs to be sufficient detail to adequately support the recommended proposal and meet the Gateway Review objectives listed above. GATEWAY REVIEW REPORTING As mentioned above, the reviewers come into the process cold and only have a few hours before the gateway review meeting to get an understanding of the project, how the concepts were developed and on what basis, whether the gateway review objectives are met, and what the potential risks are. The full assessment report, detailed study report(s) and full concept design report should be condensed into a logi- cally sequenced summary that takes the reader through the design process. In preparing the report, consider the following as suggestions: Q Q Start at the beginning – summarise key elements of the assessment including the functional classification of the route, as well as a description of the existing project section, which may have a bearing on the functional classification including: Q Q Land uses Q Q Cross sections Q Q Speed limits. Q Q Confirm the original project objec- tives and whether anything has arisen that confirms or changes them. Include other design parameters including the design period and any other pertinent information from the assessment report that had a bearing on the design. Q Q Present the outcome of the traffic loading, including: Q Q Changes in the traffic volumes along the route Q Q The basis of developing the traffic forecasts Q Q The light and heavy vehicle growth rates and forecast volumes, with the recommended sensitivity parameters. Q Q The design hour used for the capacity analysis in the geometric designs and the geometric design proposals that meet the road functional classifica- tion design guidelines and the traffic forecasts and capacity needs, recom- mended operating speeds, access man- agement arrangements, and horizontal and vertical alignments, etc. Q Q Describe the current condition of the road pavement and, using the traffic forecasts for heavy vehicles with rec- ommended sensitivity analysis, calcu- late the pavement class and alternative pavement design options. Q Q Describe the material sources and haulage requirements necessary to implement the pavement construc- tion with any risks associated with delivery. Q Q Describe the current state of the drainage infrastructure and the requirements in relation to the functional classification of the road. Logical proposals that fit the geo- metric design then follow. Q Q The same applies to the bridges and large culverts. State the methods used to determine the hydrological capacity in conjunction with the road’s functional class used in the design.