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Not so fast…caution on data collection and reporting

May 2021
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I’ve seen posts where people have offered data on bicycle counts based on short period measurements (e.g., 5 to 15 minutes). They are quick to expand the counts to hourly values. So counting 10 bikes in 5 minutes (10 bicycles/5-minutes) is reported as 120 bikes/hour. I have seen some posts even stating that this was evidence of just how many people choose cycling for their commutes. While there is a significant increase in cycling volumes since last year (probably mainly due to the lack of public transport during this pandemic), their numbers still are quite low compared to both public and private transport users. It would be nice to know just how many people are cycling compared to pre-Covid levels. Here are some data I posted 5 years ago about traffic along the Iloilo Diversion Road where they have a wide bike lane along the northbound side of the highway. One wonders about the current numbers.

Figure 1. AM Peak hour traffic along the Iloilo City Diversion Road (ca. 2016)

Figure 2. PM Peak hour traffic along Iloilo City Diversion Road (ca. 2016)

 

It’s one thing to report and another to use the expanded value for modeling or analytical work. One basic reason why traffic scientists and engineers use the expanded value is because traffic volume is generally expressed in “vehicles/hour” as a standard unit. For certain purposes, this unit is converted to “pcu/hour” or “passenger car units per hour”. Flow rates may vary and are useful to describe the flow at specific times but the variation of flow is actually more important as this describes the behavior of traffic. I know, it reads or sounds like a car-centric unit of measurement, and it is. But that same comment can be made about currency and how the US dollar is being used rather than the Euro, the Yen, or the Yuan/Renminbi…if you get my point.

Perhaps a better argument is to use persons/hour/direction as the unit of measure if people cannot agree about using a specific vehicle type? That should be more acceptable to most people. But you need to have information about vehicle occupancies. Past studies in Metro Manila have established, for example, that on average the private vehicle occupancy is between 1.2 to 1.6 persons per car. This and other vehicle occupancies are multiplied to the various vehicle to estimate the number of persons in persons/hour/direction traveling along roads. This can be for the entire day or for peak periods. Note though that occupancy values will also vary according to time of day. The same calculations can be applied to rail and other modes as well.

The classic and popular graphic comparing the road space occupied by cars vs. spaces occupied by buses, motorbikes or bicycles, respectively is also inaccurate as these show capacity or the potential high value if certain modes are used. There will never be a 100% single mode choice especially for major roads like say the urban street network. Most people will choose their mode of transportation based on many factors including travel distance, time and cost. Those are the measurable factors. Others like comfort and convenience are also important and perhaps may have other factors substituting for them.

While I support cycling and the provision of bike lanes, there should always be a fair treatment of how data or information are gathered and presented. Otherwise, we are just misinforming people and generating hostility where cooperation or collaboration should be pursued instead. More work or effort towards convincing the general public and especially decision makers and movers in government and the private sector to effect changes in policies and infrastructure requires being collaborative rather than combative. That includes formulating ang communicating solutions rather than playing a blame game.


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