Spatial Analysis of Transportation System of the Planning Area The Missing road links in spatial analysis

The study on Master Plan for Urban Transport in the Nairobi Metropolitan Area (NUTRANS) (Katahira and Engineers International, 2006) identified several missing road links within the Nairobi Metropolitan region, a number of which are found in the study area.

The missing links 3, 6 and 7, namely, the Turbo road - Lenana road – Kileleshwa ring road – James Gichuru road links from study zone 4 to zone 5. The construction of the Missing Links No.3, 6, and 7 is currently underway to connect each separated residential zones and to form a western part of urban radial and circumferential network system which will increase accessibility for mitigating traffic congestions.

The other missing road links identified in the study are Missing Links No. 15a, 15b and 15c from Westlands to Gigiri (within the study zones 3 and 13 and 20B). The Missing Link No.

15a and 15b are under construction while No.15c through Karura Forest will begin after agreement with the forest authorities is reached. It should, however, be noted that this area is of difficult and inflexible terrain with a lot of construction constraints, including the Karura forest. The other missing links being constructed are the UNEP Avenue – Ruaka road – Kiambu road under passing the Eastern by-pass (in the study zone 13). The other missing road link under construction is in Parklands (study zone 3).

The Eastern by-pass from Jomo Kenyatta Airport, across Nairobi-Thika highway at Ruiru passes through the study area zone 13; its completion is however equally important for the zones 3, 4 and 5 for it will provide efficient traffic connection to other areas outside the study area.

The completion of the construction of these missing road links to design, fully integrated with NMIMT facilities, will give some relief to this rapidly developing study area. A transect survey revealed, however, that the road reserves for the links 3, 6 and 7 are still narrow and it remains to be seen whether the roads will be fully integrated with NMIMT facilities.

efficiency of the functionality of the roads during rains. This also leads to erosion and quick deterioration of the roads and streets. This always results in poor environmental quality.

During the stakeholders‘ forum, a numbers of examples were given where the drainage systems are a problem. The widely acknowledged example, however, was the Waiyaki way.

Spatial analysis of congestion and quality of road transportation system Narrow roads and reserves

A transect survey of the transport network of the road transport system revealed that all the roads of the study area, with exception of only the Waiyaki way, were narrow with narrow road reserves, posing a stringent constraint to any form of expansion of the roads in the area unless good partnerships are built with the residents and lot owners and their associations to contribute land. This is due to the fact that this is an already built-up and fully developed area. The other option is conditional approval of development proposals in a strategic manner.

All the roads in the study area, with exception of the Waiyaki way, are not only narrow but also 2-lane two-way traffic roads. This increases the occurrences of bottles necks and road crashes and accidents.

Inadequate integration of the roads with NMMIT and public transport system

All the roads in the study area and/or abutting the study area, with exception of Ngong road, Waiyaki Way and perhaps Limuru road which has recently developed with narrow walkways, have all not been integrated with NMIMT and public transport facilities. Cycle and footpaths and walks are absent. NMIMTs share the same travel way with motorized vehicles. Given the different speed capacities, NMIMTs slow down motorized traffic, gradually increasing density, reducing flow and resulting in congestion and traffic jam. This sharing of the travel way between the motorized traffic and NMIMTs also results in road crashes and accidents as a result of conflicts among the mixed traffic.

Although most of the roads are being plied by public service vehicles, they are narrow and have no designated public service vehicle bus stops, only narrow/small makeshift bus stops are utilized by PSVs. The PSVs thus stop right on the road thereby blocking other traffic that is moving through to their destinations. This is again a serious cause of congestion and system inefficiency.

Bottlenecks at junctions

In the study area, both the residential neighbourhoods and commercial centres are structured with a grid system of road network. The grid network, though good for residential neighbourhoods, experiences junction dysfunctions as the rate of motorization increases. The direct linkage of the grid neighbourhoods to various transport corridors or primary roads creates a lot of unnecessary intersections that interfere with traffic flow, therefore reducing

the efficient flow of traffic on arterial roads and other heavy traffic roads. The junctions in the study area are increasing becoming bottlenecks as traffic volumes traversing these roads increase. These may necessitate the redesign of these junctions.

Measuring traffic congestion

The volume to capacity (V/C) ratio was used to establish the congestion levels on the various key roads in the study area. In order to compute the V/C ratio, the assigned volumes on the road network was divided by the capacity of the corresponding road links. Based on the analysis and computation of the V/C ratio, the road transport system performance has been evaluated to determine occurrence of congestion. The results for the year 2010 for a subset of links in the study area are given in Table 1(as derived from traffic volumes in Appendix 1).

Table 1: The volume/capacity (V/C) ratio congestion measure

Road Name V/Ratio 2010 System operation performance

Ngong Road 4.79 Congested; over capacity

Chiromo Road 2.71 Congested; over capacity

Limuru Road /Muthaiga Road 1.98 Congested; over capacity

Kiambu Road 0.46 Uncongested; below capacity

Waiyaki Way 3.62 Congested; over capacity

Parklands Road 4.42 Congested; over capacity

James Gichuru road 1.98 Congested; over capacity

Lower kabete road 1.29 Congested; over capacity

Arghwsings kodhek 2.75 Congested; over capacity

Chiromo road 2.71 Congested; over capacity

Naivasha road 4.37 Congested; over capacity

Forest Road 8.83 Congested; over capacity

The results for 2010 indicate that majority of the roads under analysis in the study area and the neighbouring roads were operating above capacity meaning they were experiencing congestion. The Forest road, neighbouring the study area presents the worst case with a V/C ratio of 8.83 while Kiambu Road was operating below the capacity with a V/C ratio of 0.46.

The performance of the roads is not satisfactory at all. This means that if nothing is done about the congestion situation in the study area, the congestion levels are set to continue rising to unmanageable levels resulting in gridlock.

Diversion of traffic from the congested roads such as Naivasha road, Ngong road, Waiyaki road and Thika road into the roads within the study area such as James Gichuru road,