Macroscopic Simulation Approach of Public Transport on Exclusive Lanes
A Valencia, Pontificia Universidad Catolica de Valparaiso, CL; R. Fernandez, Universidad de los Andes, CL
A macroscopic simulation approach which represents the operation of public transport vehicles on exclusive lanes is shown. The approach has shown to be better than simplified analytical models and less complicated than microscopic simulation.
This paper presents a macroscopic simulation approach that describes the operation of vehicles on public transport exclusive lanes with enough detail to take into account all sources of delays: at road sections, traffic signals, and bus stops. This approach has been encapsulated in a simulation model 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 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 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.
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. These components are additive and they allow the analyst to estimate the commercial speed ? average speed between one origin and one destination stop, including all sources of delays ? as the mean measure of effectiveness. Other measures of effectiveness are delays and degree of saturation at junctions, as well as capacity, delays, queues and degree of saturation at stops. We used up-to-date traffic theory to describe these sources of delay and ad-hoc models to evaluate the optimum stop spacing and delays, queues and number of stops at bus stops.
In the paper we review the constituent parts of the model that allow the user the study of measures in a whole arterial road or at specific junctions and stops. For example, at bus stops the user can evaluate the appropriate number of berths and advantages of providing overtaking facilities; at traffic signals the user may take decision about best signal timing which reduces delay to buses; at arterial level the user can assess which is the optimal spacing of bus stops.
The impact of various traffic measures has been tested with the model, such as the optimum stop spacing, number of berth and overcoming facilities at stops, and signal timings that considers the progression of public transport vehicles. As a result, we have found that commercial speed can be improved between 9 to 20% if stop are optimally spaced. A further 2 to 7% can be achieved if overtaking facilities are provided at stops. If traffic signals are set so that they take into account the bus progression, an additional 3 to 5% increase in commercial speed is attained. In summary, beyond the sole segregation of buses and cars, if appropriate management schemes at junctions and stop are implemented in a segregated bus lane or busway, the commercial speed in an arterial road can be improved between 15 to 30%.
The model has been validated against real data in a busway in Santiago de Chile showing an average discrepancy of less that 1% in the commercial speed. Therefore, this work delivers a new tool which may be useful to both, public transport operators and transport modellers wishing to understand the impact on travel times as a consequence of tactical changes in operational variables of public transport. The advantage of our approach over more sophisticated tools (e.g., traffic microsimulators) rests on its simplicity for testing public transport management schemes on the street, allowing the evaluation of policies easily and quickly. In this sense, it is an intermediate approach between simplified analytical models and microscopic simulation.
Association for European Transport