Just a stupid idea I've been playing with (relating to the previous article). These numbers are just made up, I would need actual data to do this properly. Here's the scenario:
You have a road with 100 car users. They travel at an average speed of 50km/h on a road of 1,000m in distance. Suddenly, Joe Bloggs decides to ride his bike. Due to a lack of a cycle path, he uses the road he used to take his car on. So the new situation is this: 99 car users on a road of 1,000m. Lets assume that as there has been a 1% decrease in the number of cars, that corresponds to a 1% increase in the average speed (I have no idea what the actual ratio is - this also doesn't take into account the speed limit - which might be 50km/h - or road capacity etc), which is now 50.5km/h.
When we factor in Joe Bloggs, traveling at 20km/h , we have a new problem. Cars were traveling at an equal distance from each other in a nice, flowing manner. But when Joe joins the road, hugging the left hand curb, cars have to slow down, wait for oncoming traffic to be clear (relatively - i.e. no big truck approaching), then move slightly to the right before overtaking and continuing at 50.5km/h. However, this slowdown has an effect on everyone behind Joe. Assume that each car is inconvenienced by 10 seconds (generous, it's likely more) and has to slow down to 30k/h for that time. Prior to Joe converting to a bike, it took commuters 1 minute and 12 seconds to reach the end of the road (going at an average speed of 50km/h).
The 0.5km/h speed boost translates to a 1 second gain for each vehicle, or 1 minute 35 seconds, plus the 1 minute 12 seconds from Joe -- great, Joe has reduced overall congestion by a whopping 2 minutes and 45 seconds - that must be great for the environment! However, when we factor Joe the cyclist into the equation, the 10 seconds that users are stuck at 30km/h results in only 83.333 meters traveled in that time. Subtracting this from the 1,000 is: 1 minute 5 seconds (to travel 916.666 meters at 50.5km/h) plus 9 seconds (83.333 meters at 30km/h) equals 1 minute 14 seconds of travel time, an increase of 2 seconds of travel for every other commuter, not the 1 second decrease we had expected. So now we have to shave that 1 minute and 35 second gain off and instead add 3 minutes and 18 seconds (2 seconds for each of the 99 vehicles left). Subtracting Joe's savings of 1 minute and 12 seconds of commute time by not driving his car, the increase in commute time becomes 2 minutes and 6 seconds (or 0.75%), thereby causing more damage to the environment and more congestion than if Joe had driven his car.
Make sense?
