Freight Travel Time Reliability On The Northern Corridor
More than common congestion, transport reliability is emerging as an issue of greater concern on freight corridors. It has been estimated that costs associated with unpredictable travel form the bulk of the logistics costs of freight transport on the Northern Corridor, against much lesser direct delay costs. To assist the course of reliability on the corridor, this study evaluated freight travel time reliability on a key logistics stage section, the Northern Corridor Road segment in Nairobi. Applying a modelling approach to measurement with freight travel time data collected along the road, the travel time reliability measures planning time and buffer time were compared with the travel time measure average travel time over time for trip scheduling purposes and the travel time reliability measure reliability index was compared with the travel time measure mean travel rate over time for performance evaluation purposes. The results indicated that freight travel time reliability trends are inconsistent with freight travel time trends on the segment. From the trends, the ideal and unideal freight travel periods were identified and it was indicated that it is over four times more beneficial to transport freight during periods of high reliability than during periods of low reliability. The segment also performs dismally with freight reliability index values ranging from 100% to 400% compared to an acceptable threshold of 100% and compared to more or less similar function roads. It was also determined that the study adds to previous congestion studies of the road segment with pointing out the need to treat unexpected delay much as the previous studies pointed out the need to treat expected delay. Further, shortcomings on the segment were prioritized for improvement. It was indicated that providing the trip scheduling information from the study to users through the website of the agency responsible for management of the road segment, with accessibility enabled on mobile devices, would improve the reliability of their travel plans. The influence factors of the segment freight travel time and freight travel time reliability performance were identified as the mainly commute use of it; traffic incidents and roadway abuse coupled with inadequate traffic control. Possible improvements measures were therefore determined as truck-only facilities; an incident management programme and a ramp metering control system, these in addition to traffic separation strategies; traffic signs; signal-controlled junctions and traffic rules enforcement that have already been proposed in the previous studies of the road segment.
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