Essay on why efficient urban transportation needs to use the third dimension

[afransen]

An essay that some here might find interesting.

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The other day I read a paper promoting “robocars†and related technologies and I ran into the following quote:
“There are two weaknesses in the PRT idea.
1. The need to construct new infrastructure. PRT proponents argue that the guideways would be light, requiring little space.
2. There is no good reason why the vehicles must be held captive to the guideway. Vehicles captive to the guideway are called Single Mode (SM) and those capable of operating off the guideway are called Dual Mode. (DM) There has been considerable discussion of the merits of each approach.â€

Let me quickly address the author’s second assertion. I would point out that the obvious reason for holding a vehicle captive on a guideway is speed, which clearly relates to issues like safety and weather. The author indicates, through this assertion, that he envisions improvements that are, at best, incremental. OK; on to the main topic.

The article got me thinking about something that many PRT advocates seem to get, but many otherwise rational and educated people completely miss. I will state it as bluntly as possible, because it occurs to me that only very distilled concepts seem to get traction (and funding) in our society. You know, “war on terror,†“no child left behind,†etc. Effective leaders understand the power of a sound bite. I know that I am “singing to the choir,†and I know my readers are much more astute than most, but I have heard too many discussions where even the most well-read PRT people stumbled around on this issue. So here it is, boiled down to two pithy sentences, ready to pull out at the next opportunity.

Efficient urban transportation at ground level is a physical impossibility. Therefore the best transit solution will necessarily require a whole new infrastructure. Period. End of story.

It is simple physics. Objects moving in different directions on a single plane will either bump into each other or have to wait for each other. This is the universal truth behind traffic. By moving in groups this effect can be minimized somewhat but never eliminated. The best solution to urban congestion, by far, is to move in three-dimensions. This, and only this, gives many-fold, rather than fractional improvement.




(Continued)

 

[sjc]

Efficient urban transportation at ground level is a physical impossibility. Therefore the best transit solution will necessarily require a whole new infrastructure. Period. End of story. It is simple physics. Objects moving in different directions on a single plane will either bump into each other or have to wait for each other.

It is important to consider cost-effectiveness. This is why many roads are not grade separated; it is not worth the cost of doing so for every road.

For transit, putting some of it underground (or above the ground) may make sense, while supplementing the underground transit with local surface transport (like the TTC does with busses and subways). While we could likely use a few more subways in Toronto, there is no absolutely no need to replace every bus route with a subway.

Transit (and/or robocars or whatever) needs to balance cost, time and efficiency. While you might have to wait at an intersection for others to go by, would the time saved by grade separating the intersection be worth the cost? In high density areas it might be worth doing, in lower density areas not so much.

 

[afransen]

It's not just the time saved by not waiting at intersections. Once the network becomes sufficiently congested, you have to come to a complete stop at nearly every intersection. Average speeds for cars in a dense area during peak times is languising in the high 20s to low 30s kph (and sometimes less). Buses are even worse. There is a huge economic cost to this lack of connectivity.

The rest of the essay speaks to whether it is worth the cost for grade separation, or at least how you make that grade separation affordable. He argues that the best way to accomplish this is to only move the light things: people. Having to build infrastructure that can support ten, twenty, or thirty ton vehicles is what drives the cost. Seeing the absolute mess that is transit in Toronto also make a pretty convincing case for why subways won't be a solution for 95% of the geographical area of the city. It's just too damned expensive.