The impact dedicated bus lanes have on traffic.

I read this article today with regards to the increasing number of solo drivers.

City roads crowded with solo drivers... Read More

What I found interesting were the comments. One person suggested if we travelled at faster speeds instead of the slower speeds now being imposed on roads we could move more cars, but others in turn suggested faster speeds actually reduce the amount of cars. I thought that was an interesting conundrum. The faster we go the less cars and thus people can be moved through a given section of road over a given time. I decided to investigate the maths to determine who was correct.

The main factor is safety and the safe driving distance between cars at higher speeds. For the calculations I assumed the average car was 5m in length. The safe distance between cars is suggested to be two seconds which works out to be 33 m, 44 m and 55 m at 60 km/h, 80 km/h and 100 km/h respectively. Thus at higher speeds cars are the same size but the amount of space they require for safety increases, thus resulting in less cars per kilometre. That is in a kilometre for cars travelling at 60, 80 and 100 km/h there would be approximately 26, 20 and 16 cars respectively.

To take the maths a little further, I determined that over an hour the number of cars traversing a kilometre at 60, 80, 100 km/h there would be 1578, 1,224 and 1,000 cars respectively.

What I felt was interesting was I felt this showed me a few things. On roads where there is light traffic low speed limits could result in less cars being able to travel through a given area than otherwise could. We’ve all seen those 40kph signs which don’t make much sense in certain areas. I hope the safety of people have improved otherwise there may be no gain for anyone, except perhaps increased revenue through fines.

Another thought is when you are stuck moving slowly with the traffic you may be taking longer to get to where you want to go, but at the same time more people are able to get to where they want to go.

The reason I titled this article “the impact dedicated bus lanes have on traffic” is if you remove one lane then the effect is far more drastic on traffic. In Manningham Road one of three lanes is now dedicated to buses and that means one third of the number of cars that could be travelling through the section has now been removed and there is no way to recover that loss. Using the figures above the bus lane could move 1,578 extra cars per kilometre per hour, with 1.2 people per car that would amount to 1,893 people. Each hour on that section of the road there are roughly 21 buses. Assuming 60 people per bus (the average is I suspect around 10) that is 1,260 people. Given the buses were only delayed and no additional buses appear to have been added, there has been a significant reduction in the road system to move people as a result of the bus lanes.

Whilst the headline for the published article was designed to attract attention regarding single driver cars, for me it provided an insight into the trade-off of higher speeds versus increasing the capacity to move people at lower speed. In addition the information I determined enabled me to put a more concrete figure on the reduced capacity caused by bus lanes, and if thought process is extended, there are many roads which have now been reduced to a single lane whereas in the past they had two lanes. If these roads were again opened up to two lanes the capacity of our road network to move passengers could be greatly increased at very little cost.

I can see a future where automation could potentially reduce the distance required by cars at higher speeds which in turn would increase the capacity of our roads. We also need a government which keeps a balanced view and not just prioritise its own facilities over other road users. I accept however it can be a difficult balancing act.

- Kelvin Eldridge
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