Quantitative Analysis of Urban Traffic Assignment Under Congestion Pricing in Abuja

Congestion pricing has emerged as a policy instrument for managing urban traffic demand in cities globally, with growing relevance to rapidly urbanizing Nigerian cities where infrastructure expansion cannot keep pace with vehicle population growth. This study conducts a quantitative analysis of traffic assignment patterns under alternative congestion pricing regimes in Abuja, Federal Capital Territory, Nigeria. A traffic network model representing the Abuja road network with 48 nodes and 112 links is calibrated using traffic count data from the Federal Capital Territory Administration. User equilibrium traffic assignment is solved using the Frank-Wolfe algorithm under existing toll-free conditions, generating baseline link flow and travel time estimates validated against field observations. Four congestion pricing scenarios are then simulated: cordon pricing around the central business district, link-based pricing on identified congested corridors, distance-based charges, and time-of-day pricing. System optimal assignment is computed as a benchmark for maximum network efficiency. Results indicate that time-of-day pricing achieves the greatest reduction in network-wide vehicle travel time, lowering average peak-hour commute time by 22 percent while generating an estimated daily revenue of N34 million. Cordon pricing offers a simpler implementation pathway at a moderate 14 percent travel time improvement. Equity analysis reveals that lower-income commuters bear a disproportionate burden under all pricing schemes, necessitating targeted exemptions or revenue recycling mechanisms. Recommendations include piloting time-of-day pricing on two high-congestion corridors. Keywords: traffic assignment, congestion pricing, Abuja, user equilibrium, network analysis