US vehicle miles driven continues to plummet; trends predict more bicycling, walking & transit

The Federal Highway Administration's monthly tally of motor vehicle miles traveled shows that those miles driven continue to plummet.

The December 2008 figures (the latest available) show that motor vehicle miles traveled were down about 3.6% for 2008 as compared with 2007.

Three thoughts:

1. It is remarkable that miles traveled continued to decline quite sharply even in the last part of 2008. During that period, gas prices were declining dramatically--which creates a strong incentive to drive more.

U.S. citizens continued to drive less even when the incentive was to drive more.

2. This continued drop in miles driven dramatically upsets transportation planning as it has been done over the past 50 years in the U.S. All road and highway planning is done on the assumption that travel miles will continue to increase at a 2-4% annual rate as they have done (on average) through the entire 20th century.

Now--even after the U.S. recovers from the current economic difficulties--predictions are for miles driven to grow less than 1% annually (see below).

Most road projects are planned using 10, 20, and 50-year traffic forecasts. Even just 10 years out, the difference between 1% and 3% annual growth rate is very large. Tw
Projection of vehicle miles traveled: What we thought vs what is happening now. Source: Missouri Bicycle Federation. Click for full-sized version.
enty years out it's a 2:1 difference.

Are we planning our roads for twice the traffic that will really exist in 20 years?

3. A small change in motor vehicle trips causes a large change in walking, bicycling, and transit trips.

The difference in the amount of motor vehicle traffic in a year is relatively small--barely noticeable to a casual observer.

However, when those few small percentage points of motor vehicle trips become walking, bicycling, or transit trips, the proportional increase is huge.

Walking, bicycling, and transit together account for only about 6% of trips in Missouri.

About half of the reduction in motor vehicle trips is transferred to walking, bicycling, or transit trips.

That means that 6% of trips has (in one year) become more like 7.5% or 8%. And that means, in proportional terms, a big increase in walking, bicycling, and transit trips in a single year.

Increases in ridership of about that size have indeed been reported by transit agencies. Anecdotal reports from all around Missouri indicate large increases in the amount of bicycling and walking as well.

These figures also indicate we need to change our transportation thinking rather dramatically: instead of planning for huge annual increases in motor vehicle miles traveled, we need to be looking out for how to safely handle the greatly increased demand for new walking, bicycling, and transit trips.

The Future Isn't What it Used to Be
No one expects the number of motor vehicle miles driven to keep decreasing forever.

But a fascinating analysis by Todd Litman of the Victoria Transport Policy Institute (PDF) gives a lot of good reasons to think the amount of motor vehicle trips w
US vehicle ownership rates have been level since about 2000. Source: Todd Litman, VTPI. Click for full-sized version.
ill level off or grow far more slowly, rather than keep growing at the 2-4% annual rate they have grown for the past century.

1. Over the twentieth century, the number of automobiles in the U.S. has grown from practically none (about 1900) to one per household (about 1950) to more than one per licensed driver (2000). Growth in the number of motor vehicles just can't keep going up because there is nowhere for it to go.

American love their automobiles, but how many cars per person do we need? Or can we afford? We are close to the limit--the peak in the number of cars per capita may have been reached in 2000, according to FHWA data.

2. Future growth in motor vehicle miles traveled is likely to be proportional to population growth, around 0.9% annually, rather than the super-growth rates of 2-4% per year we saw during the 20th century. A growth rate that high simply can't continue forever.

3. The U.S. population is aging. Older citizens drive less--but walk, bicycle, and use transit more. This demographic shift will only accelerate the trends towards less driving and more walking, bicycling, and transit use.
US vehicle miles driven--a longer-term look. Source: Todd Litman, VTPI. Click for full-sized version.

We need to spend more of our resources planning and building for walking, bicycling, and transit, and less building for growth in vehicle miles traveled.

That doesn't mean bicycling, walking, and transit should get all resources and motor vehicles none! All indications are that the motor vehicle will be the dominant mode of transportation in the U.S. for a long time. And certainly it will continue to receive the majority of transportation funding.

But these trends mean we need to tilt our priorities in a somewhat different direction--a little less towards cars and a little more towards walking, bicycling, and transit.

Spending, say, 10% of transportation dollars on bicycling and walking and another 10% on transit over the next decade would quite literally transform the state of Missouri.

That is the direction the American public wants and the direction the future is going--like it or not.

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