The flyover at Six Miles

David Abrikian, Guest Columnist

Since the construction of the Six Miles flyover decades ago, access in and out of Kingston on its western side has been greatly streamlined, as traffic leaving the city from either Spanish Town Road or Washington Boulevard can head out non-stop to the countryside along Mandela Highway. The same is true for traffic approaching Kingston, heading in the direction of either Washington Boulevard or Spanish Town Road.

Further, for intra-city traffic, the route from Washington Boulevard to Spanish Town Road also facilitates non-stop traffic. But what about in the other direction? Most of us will recall that if one is heading from Spanish Town Road back in the direction of Dunrobin Avenue, one still has to wait for a lull in westbound traffic leaving the city, before crossing on to Washington Boulevard.

But it appears that streamlined, undisturbed, continuous traffic could have been facilitated in all directions, from all directions, with the use of a single flyover at the Six Miles junction.

Existing Arrangement

Figure 1 depicts a schematic layout of the flyover as it currently exists.

Route P1 could be considered the key route in this flyover arrangement, as this, the elevated route (coloured purple), that enters the city (via Spanish Town Road) and which 'flies over' the 'ground-level' route B1 that leads out of the city (via Washington Boulevard).

One should note, from actually driving on it, that Route P2 is also elevated. But when examined carefully, it becomes apparent that this was not necessary, as Route P2 does not need to go over any other route in connecting incoming traffic to Washington Boulevard.

Incidentally, one might also note that Route P2 has an outward bend in the northerly direction, which again appears to be unnecessary, apart from the fact that this bend accommodates the curved bulge in Route P1. However, as far as the flow of traffic is concerned, Route P2 is fine.

Routes Y1 and Y2, which lead from Spanish Town Road to Mandela Highway and from Washington Boulevard to Spanish Town Road, respectively, are also continuous and undisturbed.

But there are problems concerning Routes B1 and B2.

Both Routes B1 and B2 pass under the flyover route P1, the former going from Washington Boulevard to Mandela Highway, and the latter from Spanish Town Road to Washington Boulevard. As both of these routes are at ground level, by necessity they must cross each other, their point of crossing being denoted by the symbol X on Figure 1.

In terms of priority, precedence has been given to the outgoing route B1 which, therefore, always facilitates continuous traffic. As a result, however, vehicles on Route B2 must wait until there is a lull in B2's traffic before being able to get on to Washington Boulevard.

Possibilities for continuous flow

So what arrangement is there that would enable all routes to be streamlined and continuous?

One possible schematic arrangement is shown in Figure 2, in which the two incoming routes and the outgoing route from Washington Boulevard to Mandela Highway (again coloured purple) would together form the flyover. In this scenario, one of the former routes would include a complete loop in its configuration in order for it to satisfactorily merge with the 'receiving' road.

Another possibility that facilitates totally streamlined flow is shown in Figure 3, in which case the Mandela Highway-to-Spanish Town Road and the Spanish Town Road-to-Washington Boulevard routes would form the flyover, with the former, once again, using a loop to obtain its alignment.

There are probably more possible arrangements.

It is important to note here, however, that these figures are merely schematic layouts which, if ever they were to be implemented, would require proper designing and dimensioning, in order to allow for wide enough bends in the routes, among other things. This brings us to another consideration. Should the existing arrangement be modified?

Instead of attempting to answer this question, I will merely list what appear to be some fairly self-evident pros and cons of such an arrangement, starting with the latter.

Obvious disadvantages relating to modification

1. Cost: This will involve design and construction costs. The latter could be quite exorbitant, as it appears that it would be difficult to achieve a final solution without massive adjustment, if not complete replacement, of the existing structure. Of the two possible adjustments depicted, the layout in Figure 3 appears to be the closest to the existing arrangement, and even in this case there are major differences.

2. Land Acquisition: This consideration should actually comprise part of the cost, but the process of acquiring needed land can be often more involved than it seems, and hence this is listed separately.

3. Minimal improvement: An adjusted configuration would only improve the traffic flow in one of the six existing directions at the junction, namely the route fromSpanish Town Road to Washington Boulevard, the other routes currently having continuous flow.

Obvious advantages

1. The achievement of uninterrupted traffic flow along the route from Spanish Town Road to Washington Boulevard.

Finale

Only a full-fledged, cost-benefit analysis could begin to answer the question as to whether it is within the nation's interest to make an adjustment to the Six Miles flyover.

In the meantime, however, for any future municipal infrastructure designs, especially in view of the financial outlay that usually accompanies these, every attempt should be made to obtain the complete solution on the first go, instead of a fraction of same.

David Abrikian is a civil engineer. Email feedback to columns@gleanerjm.com and dpabrikian@yahoo.com.