Traffic Management Method to Study Bus Priorities on Arterial Roads
R Fernandez, Universidad de los Andes; A Valencia, Pontificia Universidad Catolica de Valparaiso, CL
The aim of this paper is the incorporation into a macroscopic traffic model the interaction between buses and cars in sections of roads, bus stops, and junctions in order to allow the user to assess measures of bus priority on arterials roads.
In a previous paper presented at the ETC 2011, Valencia & Fernandez (2011) showed a macroscopic simulation model of the operation of a public transport corridor, called CORBUS (CORridor for BUSes). The model can simulate the operation of trams, guided buses, articulated buses or conventional buses running on a segregated way, such as a bus lane or a busway. The model considers that travel time of public transport vehicles is made up of a time consumed on links at constant speed, plus variable times spent at stops and traffic signals. The model provides performance indices that allow the user to evaluate strategies for both physical and operation design of public transport lanes considering variables such as mean commercial speed, delays and queues at each of its elements. Tests with the model have proven its advantages over simplified analytical models and traffic microsimulators commonly used by traffic engineers.
This work aims to extend the representation of the bus flow by integrating the flow of other traffic. The objective of this paper is to study the incorporation into a macroscopic traffic model the interaction between buses and cars in sections of roads, bus stops, and junctions. The objectives of the paper are: (a) to review the advantages and disadvantages of models that incorporate buses as a side effect on traffic; (b) to show how to incorporate more general analytical expressions to calculate the capacity and delays in bus stops; (c) to analyze speed-flow functions in road sections with mixed traffic; and (d) to define a way to introduce the effect of mixed traffic on bus delays at traffic signals.
Since the creation of CORBUS in 2007 improvements have been made to the model. The first one was the change of the estimation of bus stops capacity, previously obtained with the Chilean simulation model IRENE. In the version presented in this work, the Highway Capacity Manual 2000 formula is used to calculate the capacity of bus stops. This will allow the user to calculate the delays at bus stops based on the boarding and alighting passengers and parameters that depend on issues such as the fare collection method, the use of doors, the passenger discipline, etc. Once capacity is calculated, delays and queues at bus stops can be estimated using the expressions of the sheared delay formula of Kimber & Hollis (1979).
Another extension is the use of speed-flow relationships with mixed traffic on road sections between junctions and bus stops. This releases the assumption used in CORBUS regarding the complete segregation between public transport and other traffic in road sections. This extension incorporates the work of Akçelik (1991) who develops a function for estimating the travel time in a road link with mixed traffic.
Finally, the calculation of delays at junctions incorporate the interactions between public transport and other traffic by using the models described in Akçelik (1995), but considering the weighted sum of public and private traffic, using appropriate equivalence factors. This makes possible to obtain the total delay per time unit: [ADE-s/s]. This rate of delay, divided by either the corresponding flow of buses or cars, in [ADE/s], will give us the average delay per type of vehicle, in [ADE-s/ADE] or [s].
All the above improvements allow the user to assess measures of public transport priority on a simple though sensible macroscopic model of urban traffic for arterials roads. These measures include: the installation of a bus lane, with or without "setback" (the interruption of a bus lane to allow right turns at junctions); the use of short bus lanes at intersections to avoid queues of cars; the effect of signals settings based on the bus flow instead of cars flows; and combinations of these measures. The article describes scenarios that display the benefits and costs of this and other traffic management schemes for public transport.
Association for European Transport