EXPERIMENTAL STUDY FOR ESTIMATING CAPACITY OF CYCLE LANES
Sebastian Seriani, Universidad De Los Andes, Rodrigo Fernandez, Universidad De Los Andes, Esteban Hermosilla, Universidad De Los Andes
The aim of this paper is the estimation of saturation flows of a cycle lane under different physical configurations, taking as case study Santiago de Chile and London.
Today cycle lanes of Santiago are reaching high levels of flow. According to the consultant Urbanism and Territory (2013) cycling is growing at a rate of 20% annually. This is observed mainly at peak hours which occur between 7-10 am when cyclists are heading to their jobs, schools and universities or in the afternoon between 19 – 21 pm when returning home.
Clear examples of high flow of bicycles in Santiago are the cycle-track Pocuro, cycle-track Andres Bello, cycle-lane Antonio Varas and cycle-lane Simon Bolivar. We choose as a case study the cycle-track Pocuro because it has the highest flow of bikes, reaching more than 800 bicycles/h measured at the morning peak hour and 1200 bicycles/h measured at the afternoon peak hour (bidirectional flows). Also this cycle-track is an important path that connects two urban districts, with different physical and operational characteristics.
Similarly, in developed cities like London, where 2% of the trips per day are done by bike (TFL, 2011), there are also some cycle lanes reaching high levels of flow. We choose as a case study the cycle-lane Tavistock Sq. because it has a similar flow to Pocuro, reaching 1000 bicycles/h (bidirectional flow) measured at the morning and afternoon peak hour. Also this cycle-lane is an important path located in the centre of the city, with different physical and operational characteristics.
The problem presented in this research is the lack of measurements for estimating the capacity of cycle lanes at signal intersections. Therefore it cannot be identified through indicators whether a cycle-lane or a cycle-track is saturated or not. For this reason there is no record of the capacity they can offer.
According to Akcelik (1995), the saturation flow is a basic characteristic to calculate the capacity of a traffic signal approach during a typical signal cycle. For a given junction approach, the saturation flow is defined as the maximum discharge rate of a queue of vehicles during the effective green time of that approach. It is well-known that at the start of the green period there is a transient period before the discharge rate reaches its maximum, which is the saturation flow for that approach. If the queue remains until the end of the green time, there is another transient period until the start of the red time. The value of the saturation flow and transient periods depends on both the traffic composition and geometric characteristics of the junction approach.
As a methodology we establish four steps. Firstly, we measure the physical and operational variables of cycle-lanes, and we investigated about international studies related to saturation flow and capacities of cycle lanes. Then we used the approach of the Road Note 34 (RRL, 1963) for measuring the saturation flow and transient periods of cycle lanes, taking as case study Santiago de Chile and London. In addition, we defined different scenarios of experiments. In the case of Santiago it was chosen four scenarios: a) one lane of 1 m wide; b) one lane of 1.25 m wide; c) one lane of 1,5 m wide; and d) two lanes of 1 m wide each. While in the case of London only one scenario was chosen: one lane of 1 m wide. Finally, the results will be transformed into design recommendations to provide an adequate level of service for cyclists.
The main results of this research shows that the cycle-track Pocuro can reach a saturation flow of 2000 bicycle/h-lane for a 1 m wide. If the wide increase the saturation flow will also rise reaching a maximum value of 3400 bicycle/h-lane for a 1.5 m wide. If there is two lanes in a cycle-track (1 m wide each) the saturation flow reaches 4600 bicycle/h-lane. In relation to the cycle-lane Tavistock Sq. (1 m wide) it can reach a saturation flow of 4000 bicycle/h-lane (double of Pocuro with a 1 m wide).
As a conclusion, this research can be used by traffic engineers to estimate the saturation flow of a cycle lane and delays of cyclists at traffic signal. This in turn can help in designing cycle facilities at transport infrastructures. The validation of our investigation can also help transport planners with the calculation of the capacity, optimum wide, comfort, and other operational costs of cycle lanes.
Association for European Transport