CURIOUS feature of the proposed Dublin Light Rail Transit system is that little attention was given the possibility of the Tallaght service operating by a direct and more populated route through Harold's Cross and Kimmage.

A major study was made of alternative roundabout routes - one via Naas Road and the other via the fodder Valley and Milltown - but the direct route via Harold's Cross was summarily dismissed on grounds that are relevant only to an on street route.

Now if the Tallaght line were to run via Harold's Cross and Kimmage it would have to operate in a tunnel for a distance of 6 to 7 1/2 kms. The longer figure assumes that because of planning permissions which the Corporation has for some reason given some still on appeal to An Bord Pleanala for housing at several points along sections of the busway reservation through Harold's Cross and Kimmage, it would be necessary to tunnel the whole way to Wellington Lane. In practice, tunnelling would probably not be needed for most of this stretch, but I have deliberately based my costing of the tunnelling option on the more pessimistic hypothesis that it would be so required.

Routing the Luas through Harold's Cross and Kimmage would cut the length of the Dundrum Tallaght route by 4 kms, thereby halving the Luas time between O'Connell Street and Tallaght from 38 to 19 minutes. And by tunnelling from Ranelagh inwards, the Luas time between Dundrum and O'Connell Street would be reduced by one quarter to 15 minutes. This would give a total journey time of 34 minutes, as against the 60 minutes required by the on street system.

Allowing also for a three minute, reduction in the proposed eight minute turnaround time, (because a tunnelled system would not be vulnerable to the delays to which an on street system is prone and which require a "cushion" at the point of turnaround), this would give an overall round trip time of 78 minutes. That contrasts sharply with the 136 minutes, required for the on street operation and would reduce the initial vehicle requirement, from, 31 to 19 - including provision in each case for a reserve of three vehicles.

The capital savings through shortening the route - which have hitherto been completely ignored - can be determined with reasonable precision on the basis of the detailed costing of the present proposal set out on pages 96 and 106 of the 1995 "Alternatives To Tallaght" document. On the basis of the consultants' figures, these savings would be about £85 million.

So far as operating costs are concerned the annual cost of drivers and inspectors, estimated at £3 million on page 31 of the January, 1994, document on "Assessment of Alignment Options" would be cut by about two fifths as a result of the 42 per cent reduction in the number of vehicles in use, thus saving £1.2 million a year.

A similar £0.25 million reduction in the cost of vehicle technicians and supervisors would, however, be offset by the need to have a staff member present in each underground station for security reasons.

In addition to the savings both in capital and operating costs that would be achieved by shortening the route, the traffic volume would also, be significantly increased in three different ways. The first of these would be through tapping extra traffic to and from the populated Kimmage - the proposed Naas Road routing would run for 4 kms through an area virtually devoid of housing; the second would be through halving the Tallaght journey time and the third through the reduction of one quarter in the Dundrum journey time both of which would encourage more people to use the service.

This combination of factors should increase revenue by at least 20 per cent; or £2.7 million which added to the £1.2 million saving in the cost of drivers and inspectors would almost double the operating profit increasing it from £4.5 million to £8.5 million.

What about the additional capital costs of a tunnelled system? The consultants have estimated the gross cost of the tunnelling involved at £300 million. But in arriving at this figure they have not only ignored the £85 million savings through the shortening of the route but have also made two assumptions which are open to challenge.

THE first of these is the assumption that tunnelling, will cost £13.1 million per, kilometre. This is out of line with the latest tunnelling costing for the road tunnel from Whitehall to the Dublin Port area - which, with a cross section 40 per cent larger - than which the Luas consultants say would be required for the LRT, is estimated to cost only £12 million per kilometre. On this basis, a Luas tunnel could not cost more than £10 million per kilometre - at most.

Another questionable figure is the consultants estimate of £16.8 million, each for underground stations. This figure seems on the high side. A figure of £12 million per station might be nearer the mark - with a vision of perhaps £2 million for stations in cuttings in the Kimmage area, where the need for tunnelling - derives only from the planning permissions given for certain sections of the Development Plan busway reservation.

Using the consultants' own figures - for all the other elements of the project, and offsetting against the tunnelling costs, the £85 million savings through shortening the route, the net additional cost of placing Luas in a tunnel from Ranelagh to Wellington Lane in Kimmage, would be £160 million, viz little more than half the £300 million suggested by the consultants. And this figure might be further reduced if, as seems probable, much of the route from Harold's Cross to Kimmage could be above ground.

This net additional cost increased of £160 million would, however, be balanced by an improvement of perhaps £4 million in annual operating surplus. And the resultant 2.5 per cent return on this additional £160 million investment, in terms of operating profit, would be somewhat higher than the return officially estimated for the existing on street project on the same operating cost basis. For that is estimated to yield an operating profit of £4.5 million on an investment of some £210 million, viz about 2.15 per cent.

Thus, if the present on street project is justified in economic terms, so also would be a modification of it involving putting the city section of it in a tunnel.

NO DOUBT the counter argument will be advanced that half of the cost of the existing project is provided by the EU, which would not finance additional tunnelling expenditure. But such an argument makes no economic sense.

To understand why this is so, it is necessary to appreciate that EU Structural Funds are not in practice determined by reference to particular projects: they are allocated globally to each member state and are then justified by applying them to particular projects that meet national and EU criteria. And because we have more projects that would meet EU criteria than can be financed by the total sum allocated to us by the Commission, the application of funds to any particular project is a notional calculation without any economic significance.

The truth is the structural funds simply enable us to undertake more worthwhile projects than we could initiate with our own resources - or, perhaps, to undertake some of them earlier than would otherwise have been possible.

Thus, given that a Government decided some years ago that the return in terms of operating profit of just over 2 per cent on the presents Luas project was adequate, it would seem illogical to turn down on economic grounds a tunnelling proposal likely to yield 2.5 per cent calculated on the same basis.

Let me sum up the benefits of a tunnel solution.

In addition to achieving as good a financial return as, or better than, is projected for the currently proposed system a decision to place Luas in a tunnel under the city area would benefit Dublin because:

1. Only in this way could the eventual demand be catered for;

2. It would liberate centre city streets that would be blocked by an on street Luas, freeing them for pedestrians and other public transport;

3. Disruption during construction would be avoided;

4. The need to demolish dwellings in certain areas and to disrupt some businesses permanently would also be avoided;

5. Transit times would be halved in the case of Tallaght and reduced by quarter in the case of Dundrum;

6. It would leave open the possibility of an LRT service being constructed to both Finglas/Ballymun and Blanchardstown at a later stage a low cost, by means of a 1 km tunnel from O'Connell Street to Broadstone, and then northwards along the abandoned rail track towards Liffey Junction;

7. The alternative of an LRT service capable of handling traffic to and, from the airport would also be kept open.

Factors hitherto ignored by the authorities that clearly need to be subjected to an independent evaluation include:

1. The gross under estimation of the post 1991 growth of employment and car ownership in Dublin;

2. That the peak hour load cannot be assumed to exceed more than 70 per cent of the load on the most, densely packed individual peak service;

3. That the best, and probably the only, way of coping with the virtual doubling of demand as between a Dundrum terminating line in the year 2001 and a Cabinteely terminating line in the year 2011 is the coupling of vehicles - a procedure that is practicable only if a tunnel is used in city areas;

4. That a partly tunnelled routing via Kimmage that would be 4 kms shorter would create an offsetting capital cost saving of £85 million, would reduce the overall journey time by 40 per cent, and would generate several million pounds of additional revenue;

5. That the net return on a tunnelled section in terms of operating profit per unit of capital expended seems likely to be similar to, or probably even to exceed, that of the existing on street project.

Against this background, I believe that it would be unwise of the Government to resist the case for an independent review of the tunnel option.