Establishing and applying speed-flow relationships for traffic on South African freeways

[摘要] ENGLISH ABSTRACT:Peak mornmg traffic-flow data were obtained from video footage of threerepresentative freeway sections on the Nl and N2 westbound towards Cape Town.Flow, speed, and density measurements were made from the footage with the aid of astopwatch.Many researchers (2-12) have originated and developed models to describe therelationships between traffic flow characteristics (speed, flow, and density) onfreeways. In this report, a number of these models have been investigated with dataobtained from South African freeways. The ability of each model to predict flowparameters over the entire range of data was evaluated with the aid of statisticalmethods. The tests were performed by regressing average speed vs. average density.Flow-density and speed-flow relationships were derived through application of thesteady-state equation (2.6). In each case, a final model was chosen through visualinspection that consisted of two separate curves, one for the uncongested flow regimeand one for the congested flow regime. Furthermore, speed-flow relationships wereexamined for individual lanes and compared to relationships established for averagelanes. The models were also compared to models obtained from overseas studies(1,16,19) as well as from studies done locally (17).A secondary objective of this study is to investigate the performance of existingfreeway facilities through application of the relevant models to the traffic-flow data ofa particular facility. The current peak-morning performance of the N2 freeway sectionis investigated in terms of travel-time and travel cost. The particular study sectionconsists of three lanes, the right hand lane being an HOY lane dedicated to taxis andbuses. Different hypothetical cases are investigated. The first hypothetical case is aninvestigation into the traffic situation on the freeway section without the influence ofthe HOY lane. The second hypothetical case investigates the traffic situation on thesection with perfect operation of the HOY lane. The current performance of the N2section is compared to the performance of each of the hypothetical cases.

[发布机构] Stellenbosch University