Reducing Peak Loads

Every morning Jess (my dog) and I walk to our local coffee shop, read the paper (she is very bright), and watch the world go by. This routine happens to coincide with peak morning traffic which has its own amusements.

Unsurprisingly, the vast majority of drivers appear unhappy stuck in traffic. But on a more technical front, I have also been struck by:

1. How few cars get through on a single traffic light change (around 6-10 in this area)
2. The large amount of road space that cars take up.  
3. Consequently, how a small reduction in cars during peak times would considerably improve traffic flow.  

The space inefficiency of cars vs bikes and buses is quite nicely shown in the following image.

No wonder there are efforts to encourage people to cycle.

In Christchurch, the latest push rests heavily on the relatively controversial development of dedicated cycle-ways. The public acceptance of their benefits has not been helped by some bad design and extremely extravagant and intrusive installations. Some wonder if the significant cost is worth it.

To add to the debate I wondered if I could estimate the impact cycling has on traffic levels by taking a rough survey from my coffee shop window.

I will be the first to admit that this is highly unscientific study. In particular, my coffee shop is on a major car, bike, and bus route vs one primarily used by cars. However, in a 30 minute window during rush hour there was an average of 15 cyclists for every 100 cars (primarily carrying a single passenger). At this time traffic is already bumper to bumper. I would suggest that if all these cyclists decided to drive significantly larger traffic problems would ensue.

I would also suggest that if this number could be increased even a small amount, say 25 bikes to every 100 cars, this would result in a significant improvement to car travel time during peak time.

While the $150million budgeted to be spent on cycle-ways over the next 5 years seems like a large figure, if it improves peak loads it may be a comparatively good use of money. Given that the council already spends around $150 million every year on roads and footpaths, building cycle-ways may be a better use of money than building more roads to cope with the peak load.

In this same 30 minute window, 3 buses went past. It is easy to be skeptical about buses in Christchurch as for large amounts of the day they appear to only carry one person,  the driver!  However, at peak time these three buses carried around 100 people (roughly, I had to count quickly). Okay, some of the passengers will be too young to drive, but it would appear that buses currently halve the peak traffic load on this route. That is very significant.  Currently, bus usage in Christchurch is subsidised to the tune of $65 million a year, or $150 per resident. Compared to the figure spent on roads that does seem a lot. However, perhaps this is worth it just to reduce this peak?

The complicating factor is that cycle-ways, buses, and bus lanes usually appear empty so are easy to see as a waste of space and resources. However, this ignores the fact that even at their busiest they will always appear empty because buses and bikes take far less room than a comparable number of cars. It also forgets that their big benefit only occurs at peak traffic points, which is not a very long time.

Now clearly a fuller cost/benefit analysis needs to be done here. However, this analysis is enough for me to restrain my initial distaste at the seeming waste involved with empty bus and cycle lanes. I need to remind myself of basic economics and consider whether they may be the most cost-effective option despite not appearing like it. Looks can indeed be deceiving.

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On a side note – the costs of peaks is a pretty common engineering issue. Most notably in electricity generation. In New Zealand we have plenty of capacity if only power was used steadily during the day (and year). Alas, it is not, so significant costs ensue trying to smooth it out. Variable power pricing is one technique used. It is also why big electricity users are encouraged to stop production as this can be cheaper than building more generation. It is also the reason that engineers tend to be enthused by the potential for energy storage (batteries, lakes etc) as the best way to create a “greener” energy network. Better to make optimal use of what we have rather than have to build new things like windmills.