Travel Times for Various Modes & Urban Layouts

It would be great to have most places, that you want to go, just blocks away, being able to walk there. That is highly improbable, even in Manhattan, at a density of 65,000/sq.mi. Even with transit all over, journeys to various places, can take a while. There is a big impetus to reduce travel times. However the methods used, usually increase times , through holding back on new roads, putting more residents on existing roads (increasing density), relying on public transit, and other methods. 

The places, that one goes, needs to be considered. The starting place for trips, home, is often ignored. Of course it’s known and a given, but there are many criteria that go into its selection. From there, popular destinations [for each individual] are to be looked at, with work being prime, comprising about 30-50% of miles traveled.

A huge misconception is that when there are more people in a given area, trip distances will decrease, thereby cutting travel time. The chart, at right, shows that as density increases, travel time increases. Beyond that graph, based upon other information, there is a large increase in commuting times above a density of 10,000. That is also near the high level of density where transit becomes more widespread, partly due to scales of economy—which basically means, that the large amount of people allows for more routes—similar to critical mass. That transition is gradual, but most urban centers (core city & some inner suburbs) that reach that density are older. There is a wider gap for newer cities.

The 3 densest large cities (NYC, SF & Chicago), have the largest transit networks, and also the highest commuting time. There is a gap to the next densest city, but the pattern continues with LA, actually being the densest for whole urban areas (core & suburbs). Other cities and commuting times can be seen in the chart.There are advantages, other than time, for transit, such as reading & avoiding expensive parking, but overall, there are more for car use.

Now, there is not really a claim made that transit is faster. For just a few cases, that is true, on commuter (regional) rail routes, which have stops only every several miles, going to the CBD (downtown). Those better times occur when each stop is near a station & during rush hour, when the roads are busier.

Another push is for walking. Many people don’t even desire that, especially when purchases need to be carried. There can be conditions to make walking not feasible for certain times: rain, cold, heat, darkness, etc. Trying to find a location that has numerous destinations that one would like, can be difficult, and requires high density, at such a level, that there is no surface parking. Also the types of trips, for shopping, that walking would be used for, would eliminate short driving trips, not having much reduction.

Many times, comparisons are made to transit in foreign cities. Those cities have considerably higher densities. There is also a lower income and fewer drivers, still a sizable amount of car use, when available. However, the congestion is much worse, than here, despite much higher transit use & the lower car use. People are often enthralled, on visiting cities of developed countries in Europe and Asia, in respect to the transit availability. That is a huge one-sided view. That is seen from a tourist angle in limited ares, that are dense, mainly for the purpose of entertainment & sights. There would be a much different view if one had to choose  places to live, work, shop, recreate & such.

The future is not looking good. The current trend, ongoing for over 2 decades, is building more transit & neglecting roads. The results of that can be seen in the chart below. Travel time has increased & is expected to increase. Energy consumption per mile traveled is often looked at, albeit only slightly, just assuming that transit is better. That’s only at high amounts of ridership, which only occur in dense areas.  Increasing congestion & travel times, reduces energy efficiency. Cars have increased in efficiency, much more than transit & that pattern will continue. Imagine, once electric is more affordable. So, this neglect of how people wish to travel, and do, is making the situation worse. Convenience, safety, privacy & other factors, in favor of cars, are usually downplayed.

For the type of thinking that higher density leads to shorter trips needed, there is one major flaw, which is not explored in consideration. It’s mathematically based. Realize that distance is 1 dimension, and that area is 2 dimensions. So when increasing the people in an area, that is a square function. The dimensions only need to be increased by 41% to get 100% more people in the area. Conversely, for doubling density, in reducing the area covered, for the same amount of people, the distance needs to be 71%.

There are other reasons too, as to why density does not lead to the same proportional reduction in driving, such as locations determined before others mover into area. The chart below show only a slight reduction in driving miles, compared to density, much less that expected or to make it worthwhile.


About Randall
A contrarian, not for conflict, but because many decisions are made, without considering the full impact & consequences.

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