I refer to Mr Jatin Doktor's letter, "Cars or buses - which move more people?" (12 December).
Mr Doktor estimated the capacity of a road lane at 6,389 cars per hour along Upper Bukit Timah Road which would move up to 9,583 people per hour per lane. This was then compared with the bus lane carrying some 5,200 bus passengers per hour.
In fact, based on Mr Doktor's assumptions of car spacing (average car length of 4.5m and three body length spacing between cars) and a travel speed of 23 kph, there would be a total of 1,278 cars passing a specific point every hour along one lane of road. This is the throughput capacity of the road lane. Unfortunately, Mr Doktor appears to have made an error by multiplying by 5, arriving at 6,389 cars per hour, on account of the 5 km length of Upper Bukit Timah Road. The length of the road lane has no effect on the throughput capacity, in the same way that the length of a water pipe does not increase the flow rate of water through the pipe.
Based on our traffic monitoring of Upper Bukit Timah road during the morning peak hours, the throughput per road lane is about 1,500 vehicles per lane per hour. If we take the average number of persons carried by one single car to be 1.5 and that carried by a single decked bus to be 80, it would be about 5,000 passengers per hour on the bus lane, compared with 2,250 passengers by car on a normal road lane. Hence, bus lanes better utilise our limited road space and favour more people.
The bus lane scheme is one of a series of initiatives to improve bus commuters' overall journey experience. Bottlenecks at congested stretches of roads would not only delay the travel of on-board passengers, but also commuters further downstream in terms of unreliable waiting time.
With more bus priority measures, buses are able to keep to their schedules better, and bus commuters can enjoy faster and smoother journeys. Given our land constraints, we need to strike a balance between the needs of different groups of road users. We seek public understanding and support for our efforts in improving the travel experience of all road users and we thank Mr Doktor for the opportunity to clarify.
DEPUTY DIRECTOR, MEDIA RELATIONS
LAND TRANSPORT AUTHORITY