Designing for delivery: tower spotting strategies to accelerate transmission line design and construction under South Africa’s TDP2024

This paper investigates the impact of transmission line tower spotting philosophy on delivery speed, manpower requirements, and total project cost. Specifically, it evaluates the trade-offs between three spotting strategies: (i) fully standardised tower deployment (one conductor attachment height), (ii) fully site-specific optimised spotting, and (iii) a hybrid approach using a limited catalogue of tower heights and types. The analysis is conducted using digital corridor 1 modelling representative of typical South African conditions and aligned with National and

International Standards.

Nine corridor simulations were undertaken, combining three terrain classes (flat, moderate, and undulating) with the three spotting strategies. All scenarios used the existing South African

Transmission Utility tower catalogue. The modelling quantified steel mass delivered cost

(including fabrication efficiency discounts), structural utilisation and span behaviour.

Results confirm that terrain variability is a dominant driver in determining the optimal spotting strategy. In flat terrain, performance differences between strategies are minimal (detailed below). The standardised solution incurs only a marginal steel mass increase relative to the optimised design, which can be offset by modest fabrication discounts. Under these conditions, standardisation provides a compelling advantage through simplified design, improved fabrication throughput, and faster construction execution. In moderate terrain (slopes, ~ 30% span variability), sensitivity to tower height variation increases. A fully standardised solution shows a noticeable increase in steel mass and costs relative to optimised spotting. Here, the hybrid strategy emerges as the most effective compromise, recovering a substantial portion of the material efficiency benefits while retaining many of the delivery advantages of standardisation. In undulating terrain, full optimisation becomes essential. Fixed-height standardisation results in significant steel mass penalties, higher uplift forces, increased foundation demand, and greater use of heavy structures. Break-even analysis demonstrates that the fabrication discounts required to offset these penalties exceed realistic thresholds.

Optimised spotting delivers clear benefits in structural performance and material efficiency, with the hybrid approach offering partial but not complete mitigation.

The paper further highlights the broader system-level impacts of spotting philosophy.

Standardisation reduces design cycle times, limits variant proliferation, improves manufacturing productivity, and simplifies construction logistics with critical benefits in largescale, parallel corridor delivery programmes. The hybrid approach balances these benefits with improved geometric efficiency across varied terrain.

Cost and construction schedules, however, are influenced by other factors beyond those studied in this paper, which include access, land constraints, environmental approvals and terrain logistics. These risks, together with the paper recommendations, must be considered wholistically as part of the design, costing and construction considerations.

The study provides a quantitative, terrain-based decision framework to support the selection of spotting strategies aligned with CIGRE B2 PS1 objectives: accelerating infrastructure deployment, reducing skilled manpower requirements, and controlling total delivered cost. The findings demonstrate how targeted standardisation, applied selectively and supported by digital modelling, can materially enhance transmission delivery capability without compromising technical integrity under South Africa’s TDP2024.