Analysis Of Traffic Flow On Selected Two-Lane Highways In Ibadan Metropolis

ABSTRACT

Traffic congestion is a common feature on highways in many cities of the

world, including Ibadan, Nigeria. Previous studies have shown that several

mathematical traffic flow models developed to analyse congestion cannot be easily

generalised or adapted to varying situations. In addition, validation errors of some

models are as high as 60.0 %. In pursuit of the objective of minimising traffic

congestion in parts of the Ibadan metropolis, headway simulation models were

developed for the analysis of flow on some selected two-lane highways characterised

by heavy traffic.

Traffic survey was conducted on three purposively selected heavily-trafficked

two-lane highways (Total Garden-Agodi Gate, J Allen-Oke Bola and Odo Ona-Apata)

in the Ibadan metropolis. Headway modelling approach incorporating the prevailing

roadway, traffic and control conditions was developed. Field data were captured on the

three roads with a camcorder between 7.00 a.m. and 6.00 p.m. for a period of six

months as specified in the Highway Capacity Manual. Comparison of the modelling

result and field headway data were carried out using Kolmogorov-Smirnov (KS) test (p

= 0.05). A traffic flow simulator was developed to simulate the different congestion

scenarios by varying the minimum and maximum headways. Capacity analysis and

validation of the results were carried out using ANOVA methods.

Average vehicular flow of 715 ± 3, 970 ± 5 and 1118 ± 9 vph per lane on Total

Garden-Agodi Gate, J Allen-Oke Bola and Odo Ona-Apata roads respectively.

Eighteen hyperbolic headway scenarios were produced and the highest coefficient of

correlation (R2 = 0.92) was recorded at 90 percentile while 0.18, 0.36, 0.50, 0.71, 0.82,

and 0.79 were obtained at 1, 10, 30, 50, 70, and 100 percentiles respectively. There

was no significant difference between theoretical and field data using Kolmogorov-

Smirnov (KS) test (p < 0.05). Also, a total number of 171 congestion scenarios were

generated using the traffic flow simulator. Traffic flow varied between 204 and 2376

pcu per lane while headways varied between 1 and 18 seconds. The capacity analysis

produced approximated maximum flow rates of 1850, 2865 and 2881 pcu in the two

directions of travel for Total Garden-Agodi Gate, J Allen-Oke Bola and Odo Ona-

Apata roads respectively. The capacity of Total Garden-Agodi Gate was within the

recommended maximum value of 2800 pcu in the two directions of travel for two-lane

highways. The results for J Allen-Oke Bola and Odo Ona-Apata roads showed that an

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additional lane will be required in each direction of travel. The validation of the

models on the dualised J Allen-Oke Bola road showed that congestion can be reduced

by about 55.0 %. A maximum validation error of 35.0 % was obtained.

The traffic flow simulator developed successfully simulated the traffic

situations on the selected highways. The analysis of the flow yielded results that could

ameliorate traffic congestion on the selected two-lane highways in the Ibadan

metropolis.