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Higher Density Causes More Traffic Congestion


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Just when you think urban renewal in downtown would include housing that would help people part from their cars, that is not always the case. When people move downtown, they take their cars with them. Do they even bother to ride the rail transit which is two blocks from their door? Or the circulating trolley buses? No, they just drive a measly five blocks to where they work if downtown instead of walking. The suburban sprawl habits of getting around just catch up with some people because of this.

From: publicpurpose.com

How Higher Density Makes Traffic Worse

By Wendell Cox

One of the principal reasons that "smart growth" or "compact city" urban strategies cannot reach their objective of reducing traffic congestion (or reducing its growth) is that there is a strong positive relationship between higher population density and higher traffic volumes. The most fundamental requirement of smart growth or compact city strategies is higher population densities.

The fundamental problem is that as population densities rise, vehicle use also rises. Perhaps the most significant research was performed for the Federal Highway Administration, which found, generally, that traffic volumes at typical densities tend to rise at least 80 percent of the rate of population density increase (Figure 1 & Note 1). This means that if an area experiences and increase of 100 percent in population per square mile, vehicle miles per square mile can be expected to increase 80 percent.

But there is more to it than that. As more vehicle miles occur in a confined geographical location (again, a requirement of smart growth or compact city strategies), traffic slows down and is subject to more "stop and go" operation. This further increases not only the time spent in traffic (vehicle hours per square mile), but also air pollution emissions per square mile (Figure 2, calculated from US EPA data). This more intense exposure to air pollution can have negative health impacts (even as overall air pollution levels are falling).

Further evidence is provided by the Texas Transportation Institute 2000 database (from Federal Highway Administration data) for the nation's urban areas with more than 1,000,000 population. A linear regression analysis shows a strong relationship between higher population density and higher traffic volumes (Table). The formula predicts that an urban area with a population density of 5,000 (such as Los Angeles) will have traffic volumes per square mile nearly three times that of an urban area with a population density of 1,000 (such as Nashville) (Note 2).


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I can't bring myself to read anything with Wendell Cox's name on it. However, most of the downtown developments in Providence do include provisions for parking.

Part of the problem, both here in Providence and nationally, is that many of these downtown renewal projects are high end. Most wealthy (or moderately well-off) people moving into cities are not willing to give up their cars and ride the bus (New York would be a glaring exception).

However, I'm sure people moving into city centres are using their cars much much less than their suburban counterparts. As long as goods and services are within walking distance and not surrounded by ample free parking, then people will walk.

How Higher Density Makes Traffic Worse Uhm, Duh! If densities are low and traffic is good, people will never use mass transit.

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