Tanzania has recently kick-started the process leading to the construction of a key stretch of road and a bridge. The work is of major significance for East Africa as this stretch provides a missing link in the 225.3km multinational Arusha-Holili/Taveta-Voi road that links Northern Tanzania to the Kenyan port city of Mombasa. This is an important project as it will connect the 1,800km Northern Corridor to the 3,100km Central Corridor that originates at Tanzania's capital and port city, Dar es Salaam.
Tanzania National Roads Agency (Tanroads) and Japan International Cooperation Agency (JICA) signed a US$168.6 million (JPY24,301 million) contract in February 2022 to finance the Arusha-Holili Road Improvement Project. This is the second phase of the Arusha-Holili/Taveta-Voi road and is slated for completion in 2027.
This missing link is expected to “…increase the volume and loading capacity of the road, improve traffic safety and lower vehicle operating costs for the Tengeru-Usa River, the New Kikafu Bridge, and the Moshi Town Sections,” according to a JICA project brief.
Works on this phase includes dualling the route from Tengeru to Usa River (10.1km), building part of the Moshi urban roads (8.4km), construction of the new Kikafu bridge, (560m long) and building the 4km of approach roads, according to Tanroads.
In addition, completion of the road and construction of the new bridge is expected to address, “…the growing traffic volume and hence contribute to economic development and regional integration in East Africa.”
The Japanese financing was affirmed during the 8th Tokyo International Conference on African Development (TICAD 8), held on August 27th-28th 2022 in Tunis, Tunisia. However, JICA had previously alluded to the existence of issues in terms of the design and construction plans in a report. Though well identified in Tanroads’ reports, there were gaps in, “…reference data necessary for appraisal of the JICA loan project, including those for the project process review of the construction method for estimation of the work costs and for project schedules.”
“Through the TICAD meetings, we as a country have benefited immensely as we secured funding for the construction of the Mfugale Bridge, the Kinyerezi II power plant project. Now we have requested them to extend funding for the completion of three projects – Arusha-Holili road, Kigoma Port and the Zanzibar water project,” said Tanzania’s Prime Minister Kassim Majaliwa, who represented Tanzania’s President Samia Suluhu Hassan at the TICAD 8 event.
Previously, the African Development Bank (AfDB) had provided $217 million for the upgrading of the Arusha-Holili/Taveta-Voi trunk road, an equivalent to 89.1% of the project’s budgeted total cost while Kenya and Tanzania provided $15.6 million and $12.3 million respectively.
Construction and commissioning of some sections of the $245 million Arusha-Holili/Taveta-Voi road had been completed successfully following civil works that included construction of the Arusha-Bypass (42.4km) and dualling of the Sakina-Tengeru section (14.1km). The project, implemented over a five-year period between 2013 and 2018, also entailed building two roadside amenities at Tengeru, one on either side of the dual carriageway in Tanzania. It also included upgrading of the Taveta-Mwatate road (89km), construction of the Taveta Bypass (12km) and two roadside amenities, one each at Bura and Maktau along the Mwatate-Taveta road in Kenya.
Completion of the missing link between Tengeru and Moshi Town will ensure the socio-economic potential of Arusha-Holili/Taveta-Voi road is fully harnessed. The development of this stretch is expected to commence by Tanroads once the process of tendering for engineering, procurement and construction (EPC) is concluded.
The proposed Japan-funded project entails widening of the Tengeru-Usa River and Usa River-Moshi Town road sections as well as the construction a new Kikafu bridge to replace the existing structure, which dates from the 1950s and is no longer fit for purpose.
Upgrading the road and building the new Kikafu bridge is now referred to as the Arusha-Holili Road Improvement Project. This project comes soon after the finalisation of a supplementary study by a study team of International Development of Japan, and Oriental Consultants Global Co that reviewed the previous feasibility study and engineering designs of the project route.
A report that emerged out of the supplementary study proposes splitting the project into four main packages. These include the 47.2km Tengeru-West Kikafu and 5.7km KIA access road; the West Kikafu-East Kikafu including the 560m Kikafu Bridge and Roadside Station; the 50.9km East Kikafu- Holili; and the safety measures in the vicinity of the existing Kikafu Bridge.
Works on the project road entails the widening and rehabilitation of several sections totalling 107.9km, including four-lane widening 21.9 km and the 560m-long Kikafu Bridge. The report says that the rehabilitation of the existing road, especially widening some of the sections through the urban area, would call for the diversion of traffic to ensure safety.
The report by the study team, says the supplementary study carried out would help address concerns that emerged during the review of a previous feasibility study. These include the unsubstantiated design speed with the report noting, “The design speed changes from 100km/h to 50km/h frequently within a short section, which deviates from the actual travelling speed and is therefore not desirable in terms of safety.”
The report also observed that the project road has, “…multiple sections whose vertical grades do not comply with the design standards of Tanzania and have steep grades without climbing lanes, which may cause accidents due to speed drop and when overtaking by passing heavy vehicles.
“For the vertical alignment near the Kikafu bridge, the grade of the approach section is proposed to be in the range of 3.5% to 4.5% so as to limit the bridge length to about 100m.
“Considering major accidents in the past, it is recommended to set flatter grades at/near the proposed Kikafu bridge and to take appropriate measures to cope with design related issues,” the report recommends.
The previous feasibility study had proposed improvement of several roundabouts along the project road although the report says, “There was no traffic survey to validate the proposed design of those roundabouts carried out.
“Only a single future traffic demand growth rate was applied to the entire study area and encompassed all types of vehicles. It was assumed that the growth rate of heavy vehicles such as trucks and trailers in Arusha and Kilimanjaro would be different because of the disparity in population density and economic activities,” the report says.
However, the conclusion derived from the supplementary study was that the, “…assumption in the accuracy of future demand forecast in the previous feasibility report in the middle and long term may not be reliable.”
Tanzania’s road and bridge standards and manual recommend use of a design speed of 120km/h for all the international trunk roads passing through or emanating from the country.
However, the report said: “Considering the nature of the (proposed) improvement, 100km/h is considered to be reasonably applicable since the geometrical requirements of the design speed of 120km/h calls for large land acquisitions and compensation which is not in line with the improvement strategy.”
The supplementary study proposes to have the geometrical design follow the existing geometrical parameters as much as possible with minor adjustments to satisfy required K-value, which is the horizontal distance required to achieve a 1% change in the slope of the vertical curve, as required in the applied design speed of the project road.
Furthermore, the study recommends an improvement of the vertical alignment around the Kikafu Bridge and to apply a maximum gradient of 3%, considering the impact of the traffic and risk in occurrence of road traffic crashes.
The existing pavement structure of the road and bridge is said to have failures that, “…have occurred on the sections where the stabilised base/subbase course have been applied.”
Against the backdrop of the pavement failures, the supplementary study recommends not to apply stabilisation in construction of the base/sub-base course.
“In addition, following the East Africa Community (EAC) guideline, the Study also recommends the use of the Superpave mix design method to replace existing Hveem and Marshall methods. This is because the former option, “….ties asphalt binder and aggregate selection into the mix design process, and considers traffic and climate as well.”
The new study also looked into alternative bridge types for Kikafu that considered several bridge options. The team reviewed several preferable alternatives that were subjected to a detailed review by a team of experts from Tanroads, International Development Center of Japan Inc and Oriential Consultants Global.
For the concrete bridge option, at least four alternatives were reviewed including a prestressed concrete (PC) Continuous Box Girder Bridge, PC Rigid Frame (Ramen) Continuous Box Girder Bridge, Extradosed Bridge and PC cable-stayed Bridge.
In addition, three steel bridge options were also evaluated in detail, among them Steel Continuous Box Girder (Steel Slab) Bridge, Continuous Steel Truss Bridge and Steel Arch Bridge. The detailed review led the team to recommend either a Concrete Extradosed Bridge or a Steel Arch Bridge. A subsequent tripartite meeting held by TANROADS, JICA, International Development Center of Japan Inc and Oriential Consultants Global settled for the PC extradosed bridge, “…as the optimum bridge type agreed, considering maintainability, workability during construction and landscape.”
The extradosed bridge was seen as the best option for the new Kikafu bridge. This was because the option, “…provides a longer span bridge which can reduce the number of piers in anticipated rock excavation at the foundation works and provides high maintainability, minimising the expansion joint of superstructure.”
“The aesthetic view of this bridge is one of the best candidates that harmonises with the scenery of the site,” it says.
Initial bridge project costs were estimated at $49 million for four lanes and $34.2 million for two lanes with the report saying the cost is, “…tolerable to realise [that] a suitable longer span PC bridge however implicated comparatively longer construction period.”
An extradosed bridge option, the report explained, enables, “…efficiently arranging outer cables from tower to enable longer span length with using box girder.”
In addition, the proposed bridge type’s pre-stressed concrete girder has, “…high durability and maintainability.”
Tanroads had also expressed preference, “…for an integrated four-lane dual bridge due to its lower construction cost and both parties agreed that the integrated four-lane dual bridge be selected for the cross sectional option of the new Kikafu Bridge.”
The report points to a probable use of the Japanese composite PC girders solution that it says are, “…composite structures that use corrugated steel panel and steel pipe truss, in the web of a PC girder, that could be applied to the Kikafu bridge.”
“However, these are suitable when the cost of the foundation and substructure can be effectively minimised by reducing the self-weight of the superstructure,” the report says.
The timelines for the implementation of the proposed road and bridge project indicate works should have been completed and some of the sections open to traffic between the second and fourth quarters of 2021. This would have depended on whether the Japanese loan could have been provided by end of October 2016. The loan was actually signed in February 2022 and Tanroads is yet to confirm conclusion of the tendering process for the road project.
However, Tanroads issued letters of invitation for consulting services including detailed design work in March 2022. The tender announcement of the initial procurement package for international competitive bidding on project construction is expected by April 2023.
Completion of the Arusha-Holili road project is expected to improve the capacity of the entire trunk road. The report’s projection is that the traffic volume along the project road would increase at around 6% to 7% annually between 2015 and 2035. “A large number of traffic is projected between Tengeru and Usa and Moshi Town where the projected traffic demand exceeds 20,000 PCU/day in 2025 and 40,000 PCU/day in 2035,” the report says.
The proposed road’s dual carriageway sections include that from Tengeru to Usa (9.3km), new Kikafu bridge (4.0km), and Moshi Town (8.6km), totalling to 21.9km.
“The remaining sections should remain as a single carriageway until traffic demand increases and level of service of the project road worsens to an unsatisfactory level,” the report adds.
The pavement courses for the road and the bridge varies both for dual and single carriageway sections but with uniform surface and binder courses of 50mm. The bituminous course ranges in thickness between 100mm and 150mm, while the granular base ranges between 50mm and 250mm. The design also provides for an improved subgrade layer of between 150mm and 400mm.
The new Kikafu bridge’s superstructure options include PC upper and lower decks with a corrugated steel web and composite trussed web. These were presented as optional superstructures for the new Kikafu bridge, demonstrating its advantages in terms of reduction in weight, which contributes to a cost-saving foundation.
Tanroads previously expressed preference for the standard PC box as an optimum superstructure for the new bridge. This was, “…due to inferior quality assurance of the joints of the concrete decks and steel web as well as higher technical capacity in maintenance of the steel required for the said optional superstructures,” according to the report.
The project road has previously recorded pavement failure so the report recommended that no stabilisation is applied, “…in construction of base/sub-base course and apply granular materials, such as crushed fresh rock and crushed stones.”
Implementation of the project requires a RoW of 60m for two new bypasses (new Kikafu bridge with its approach section and also between Himo town, in the Makuyuni ward of Kilimanjaro Region and Holili) and RoW of 45m for the existing road section from Tengeru to Kikafu and from Kikafu to Himo.
The Arusha-Holili road improvement project would herald a new era for Tanzania and Kenya as both countries hope to achieve the initial objective of reducing the transportation costs between Arusha and Mombasa for US$0.52/vehicle-km to US$0.34/vehicle while travel time between the two destinations would be reduced to 4 hours from 6 hours.