Median Lanes: Key in Bus Rapid Transit Performance
In Delhi, India, it can be difficult to enforce curbside bus lanes. Photo by EMBARQ.
One of the most controversial aspects of Bus Rapid Transit design in Delhi has been the designation of median lanes as opposed to curbside lanes. The initial bus corridor in Delhi is based on median lanes to give priority to bus riders. Duno Roy, who set up the People’s Science Institute in Dehradun, India and The Hazard Centre in Delhi, explains his views on this controversy in the India Business Standard. The discussion involves the tension between giving priority to vehicle users or bus users. Concludes Roy: “Moving the BRT to the left lane will kill whatever potential it has left.”
A technical evaluation of the difference between curbside and median lanes supports his assertions. International experiences with bus priority measures indicate that curbside lanes result in lower travel speed for buses and, hence, longer travel times for bus commuters. The main reasons are:
- Left turns are usually higher than right turns (left turns along the entire stretch whereas right turns only at the junction)
- Encroachment: hawkers, taxis, auto-rickshaws
- Punctures or openings along the corridor
- Breakdown vehicles are left in curbside lanes
- Continuous enforcement is more difficult
In addition, the type of segregation is also important. Physical segregation, as opposed to horizontal and vertical signage, significantly reduces encroachment. Delhi has already implemented curbside lanes with painted lanes throughout the city. Implementing this type of arrangement for the BRT corridor expansion is not expected to change the current operation for buses. It will be more of the same.
As an illustration of current bus corridors with curbside lines, we can also observe experiences in other world cities. Images from Santiago, Chile illustrate the difficulties of enforcing curbside lanes even at low traffic volumes. This image shows a low-floor, low-emissions articulated bus weaving around a parked taxi and a hawker.
This image shows bus lanes encroached by cars:
Photos by Dario Hidalgo.
This type of effect is also present in Brazil, where the reported differences in bus speeds between curbside and median lanes are between 5-7 kilometers per hour, in favor of median lanes.
As a result, in the Delhi Bus Corridor, the required fleet size doubles as you move away from segregated median lanes to painted curbside lanes. At the same time, the reliability of the service drops as a consequence of of higher friction with other vehicles, pedestrians, and even hawkers.
Comparison of cycle times, buses per hour, and fleet requirement for each scenario, assuming the frequency remains unaffected:
Median bus lanes with strong segregation are the preferred option. They reduce the travel time for most users and reduce the bus fleet required (thus the cost of providing service.) Assuming that painted curbside lanes will perform at the same speeds, and with the same reliability, than median segregated lanes is not supported by evidence in other bus corridors around the world.
Regarding other concerns of the bus corridor in Delhi, read this news story on EMBARQ’s Web site.
