EDITORIAL COMMENT: Mbudzi interchange an unfolding engineering feat Of course the Mbudzi Interchange is not going to be the final solution for making traffic flow easily on the northern corridor. 

The true magnitude of the massive interchange replacing the inadequate Mbudzi roundabout starts becoming apparent to many this weekend when the four major roads leading into the intersection from the four points of the compass are closed for 1,5km in each direction, and closed for 18 months.

The US$88 million price tag, although much will be paid in local currency, should have alerted everyone that we are talking about the largest single structure by a significant margin on Zimbabwe’s road network, and explain why facile suggestions that flyovers should be built everywhere are simply impossible.

Some people appear to have assumed that the flyover was something very simple, a bit like a bridge over a railway line taking the Harare-Masvingo Highway over the intersection, and that would have been the basic requirement, but would hardly solve the problem.

At this point the Harare-Masvingo Highway is a major internal road in Harare Metropolitan, and the two side roads, Chitungwiza Road and High Glen Road, are major roads in their own right.

The major complication is that a lot of traffic on all four roads leading into the old roundabout needs to turn right as well as going straight on.

Left turning traffic was never going to be a major problem, and will not need much civil engineering even when the interchange set of flyovers is complete. All that needed was land taken over so that the slip roads could be built.

But the traffic engineers quickly saw that a lot of traffic coming out of Chitungwiza in the early morning peak needed to turn right into Simon Mazorodze Road, as well as go straight on to High Glen Road.

In the evening a lot of traffic needed to turn right into High Glen from Simon Mazorodze, as well as go straight on, and all the time the intercity traffic and international traffic needed to keep on straight through.

A major problem with right turns on a roundabout is that you have to drive three-quarters the way round the circle, and block off two of the other roads while you do this. 

This, besides the incredible density of the traffic, was what clogged that roundabout, with traffic on access roads blocked for considerable periods while other traffic went round the circle, blocking the circle road.

The roundabout, as will all roundabouts, was a lot better at handling traffic than a traffic light set, especially once property owners nearby were bought out so that left-turn slip roads could be built, but this particular one had reached its limit a few years ago.

This is the reason why the interchange has to have multiple bridges on multiple levels. Once built left-turn traffic simply uses a slip road but the actual large chunk of civil engineering has to allow traffic from each direction to go straight ahead without stopping, and turn right without stopping. 

In other words there have to be eight routes through the interchange with merging traffic in the middle leading this traffic into the four exits, one in each direction.

One major problem seen early one was the decision by Harare City Council to sell land right up to the roundabout, not even leaving enough land for left-turn slip roads. And the interchange needs a lot more land than a roundabout.

A second problem, although one more solvable, was the same council not enforcing its own town planning and allowing, by doing nothing, illegal structures to be built and illegal parking on the edges of a highway. 

So one of the early stages of the preparation was to acquire the land. This is all legal and landowners cannot refuse to sell, but the process requires valuations, usually the average of two or three values. 

But the valuation is done for industrial, commercial or residential land in that area, depending on what it was being used for, so the landowners cannot hold the Government to ransom and demand a huge premium. 

They get full value for what they own and have built, so they can buy a similar stand and rebuild nearby, but no profit.

This is one of the factors that need to now go into the town planning books, that enough land is left on road reserves and especially at major intersections to allow proper roundabouts with slip roads to be built in future when traffic lights are inadequate, and eventually to allow interchanges on the really major intersections. 

We have been told that a traffic circle costs about the same as a set of traffic lights and the multiple turn lanes at a major intersection, and many road engineers believe they are a far better solution, but it does require those building main roads to think ahead when creating road reserves so that enough land is left, and then for subsequent councils not to sell off part of those reserves, as Harare tends to do. 

Hopefully all those car sales near so many intersections are all on short-term leases and can be removed at no cost when decisions are made to make traffic flow better.

Of course the Mbudzi Interchange is not going to be the final solution for making traffic flow easily on the northern corridor. 

At some stage a major diversion highway will be needed to swing traffic that never needs to be in Harare northwest to the Harare-Chirundu Highway and north-east to the Harare Mutare Highway. 

We hope that someone responsible for planning has marked out the future road reserves. People can grow crops or feed cows on what should be leased land, but not build anything where a road will one day be needed. 

This is done on the national highway network where road reserves were set by some thinking planner decades ago to leave room for multi-lane dual carriageways.

These diversion highways will not make Mbudzi a white elephant. So much traffic on the corridor does originate or terminate in Harare, along with the growing metropolitan traffic, to make this essential even with diversions, but those diversions will at least allow some huge trucks to miss the growing congestion in Harare.

Even within Harare there are some very wide reserves for some main roads, and even room for traffic circles with those triangular corner plots, but we do notice that the council and some greedy developers working together have in recent years been less lavish and that the council likes to let people encroach on reserves. 

Some future Government and council may then have to buy up half a dozen stands to let traffic flow.

 But the huge and expensive civil engineering for Mbudzi should make people and planners think carefully about proper traffic grids. 

This is only the second such piece of interchange infrastructure, and much larger than the first, the flyover where Simon Mazorodze Road hits the city centre. 

More in time may be needed, but the land and money required mean that they have to remain the exception rather than the rule. 

Even very rich cities and countries minimise them to avoid having a major city being roadworks rather than homes, shops, offices and factories. Other traffic solutions have to be pushed to the limit, and that includes decent public transport by road and rail to reduce congestion.

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