Edinburgh finally got its tram system last year, which was over-budget and behind schedule. Most of the problems were due to having to lay the rails in the road. Why didn鈥檛 Edinburgh and other UK cities go for trolley buses 鈥� electric buses powered from overhead wires 鈥� instead of trams?
鈥� From my experience in having delivered a rail-based, road-running urban tramway within budget, I can think of several reasons why trolley buses were not preferred.
Unguided trolley busways with the same passenger capacity as tramways require far more space. Drivers of trolley buses cannot match the precision of a vehicle guided by rails, so they need more space as a safety buffer.
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Guidance systems for buses that don鈥檛 run on rails do exist, but their use of space is not as efficient as that of a tram. Such guidance systems may also prevent other traffic from using the busway and so cause congestion.
The guided busway has not proved to be an alternative to the tramway; the two systems are each suitable for different circumstances. For example, a tramway might be the right solution for transporting extremely high numbers of passengers through very limited volumes of space.
As far as budgeting goes, few tramways or guided trolley busways are built each year, so there is little experience to draw on when it comes to identifying key cost issues.
The detailed investigation needed to establish the cost of a system is in itself very expensive and potentially disruptive. Sometimes, it might be practical to carry out the exploration and construction at the same time, and to accept the resultant massive uncertainties in cost.
But, obviously, that decision is a political issue rather than an engineering one.
J. H. M. Russell, Golant, Cornwall, UK
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This article appeared in print under the headline 鈥淩ailing against it鈥�