UNIVERSITY OF NAIROBI GEOMETRIC DESIGN OF CHANGAMWE – KWA JOMVU (A109A) By Muthee Eric Mbugua, F16/36317/2010 A project submitted as the partial fulfilment for the requirement for the award of the degree of BACHELOR OF SCIENCE IN CIVIL ENGINEERING 2015
Figure 2.2. Road Reserve The following road reserve widths are applicable for the different rural road classes: Table 2.5: Rural road reserve width Functional Road reserve (m) Major Arterial 40 -60 Arterial 40 -60 Major Collector 40 Minor Collector 25 Major Local 9 – 20 Local 9 – 10 Local Access 9 – 10 The reduced widths should be adopted only when it is found necessary for economic, financial or environmental reasons in order to preserve valuable land, resources or existing development or when provision of the desirable width would incur unreasonably high costs because of physical constraints. For dual carriageway roads it may be necessary to increase the road reserve width above the given values. As a general rule the road reserve boundary should be at a distance from the centerline of the nearest carriageway equal to half the road reserve width for single carriageway roads. Table 2.6: Urban road reserve width Functional Class Road reserve (m) Major Arterial 60 – 80 Minor Arterial 20 – 45 Major Collector 18 – 40
All-purpose roads with no frontage access, no parked vehicles permitted and negligible cross traffic 1350 1500 2200 2 200 3300 Appropriate to all- purpose distributors All-purpose streets with high capacity junctions and 'No waiting' restrictions 1000 1200 1800 1 350 2250 (or 2450 for dual y Applicable to distributors and access roads where accesses is frequent but capacity is not unduly restricted by junctions All-purpose streets with capacity restricted by parked vehicles and junctions 450 to 600 600 to 750 1100 to 1300 900 to 1000 1500 to 2000 Applicable to roads waiting vehicles and with heavy cross traffic limit capacity Table 2.9: Practical capacities of one-way urban roads Effective width of carriageway in meters ( excluding refuges or central reservation) 2-lane 3-lane 4-lane 7.0m 7.3m 10m 14m Remarks
With these ideas in mind, a desk study was undertaken so as to come up with techniques for data collection. Classified directional traffic counts and Origin –Destination (O/D) studies were done at survey locations and the study programme as depicted in Table 3.1; Table 3.1: Points of Study Locations Changamwe about ( junction of A109 and A109A towards Mombasa ) Manual counts – 13th December 2011 and 14th December 2011 Airport junction (lies along A109A en route to airport) Manual counts – 13th December 2011 and 15th December 2011 Refinery junction (lies along A109A en route to refinery) Manual counts – 14th December 2011 and 16th December 2011 Kona Relly (lies at the junction heading to Miritini and Magongo estates) Manual counts – 15th December 2011 and 16th December 2011 Kwa Jomvu ( junction of A109 and A109A towards Nairobi) Manual counts – 17th December 2011 and 18th December 2011 O/D Surveys – 15th December 2011 The points are illustrated in Fig 1.2. Axle Load Surveys were also conducted on the road using a mobile weigh-bridge to be able to design a road pavement which is capable of carrying future traffic load. It also covered commodity carrying traffic such as Medium Goods, Heavy Goods, Buses, Tractors and some Light trucks. An assessment of journey times was made on Changamwe –Magongo - Kwa Jomvu – Miritini (A109A).The details of this study are given in Chapter 4. Topographical Survey The survey was carried out by mapping from aerial photography. A digital terrain model was generated from the aerial photography which was then used for generating the profile. Climate and Rainfall Data The area experiences a bimodal rainfall pattern, with long in March-May and short rains from October-December. However a relatively wet, narrow tropical belt lies along the Indian Ocean coast. Behind the coastline large areas of semi-arid and arid desert lands stretch. The project area receives an annual rainfall that ranges on average between 544-1784mm in the narrow tropical belt represented by the available data for Mombasa airport. The rains are much influenced by the proximity to Indian Ocean. The movement of air masses, between the two high pressure belts in the south
The drainage structures mainly consist of pipe culverts, mitre drains, scour checks, and catch water drains and outfall drains. The proposed new structures are presented in Table 6.1 below. Table 6.10: Proposed structures Item Chainage Existing Structure Proposed Drainage Structure (A) CHANGAMWE-KWA JOMVU( A109A) 1 4+500 4x 900 PC Retain existing culverts 2 4+400 1 x 900 PC Retain existing culvert 3 4+200 1x 900 PC Retain Existing culvert 4 4+000 1 x 900 PC Retain existing culvert 5 3+800 1 x 900 PC Retain existing culvert 6 2+750 1 x 900 PC Retain existing culvert 7 2+000 1 x 900 PC Retain existing culvert 8 0+560 2 x 600 PC Replace with 2x900PCC 9 0+000 - 0+750 LHS 1200 PC New underground drainage system 10 0+050 - 0+4800 LHS 1200 PC New underground drainage system 11 4+700 - 4+900 RHS & LHS 1200 PC New underground drainage system 12 5+000 - 5+100 RHS & LHS 1200 PC New underground drainage system (B) CHANGAMWE-MIRITINI( A109) - AT KWA JOMVU INTERCHANGE 1 0+450 - 0+665 1200 PC New underground drainage system 2 0+560 - 0+900 1200 PC New underground drainage system Bridges There are several bridges designed on both roads A109 and A109A mostly due to the interchanges at grade separations and crossings at the railway line. These include: Changamwe Interchange Bridge A109 2 Bridges along A109A Kwa Interchange Bridges; One across A109 One across A109A