בשעות העומס: ירידה קטנה במספר המכוניות גורמת לירידה גדולה מאוד בגודש התנועה

נשלח 20 באוג׳ 2009, 6:15 על ידי Sustainability Org   [ עודכן 23 בפבר׳ 2011, 23:53 ]
Published: 2009

In June 2008, INRIX published the groundbreaking INRIX National Traffic Scorecard (available at http://scorecard.inrix.com). Using data from 2007, the initial Scorecard provided a comprehensive and consistent overview of where and when congestion exists on the major roads in America’s top 100 metropolitan areas. This 2008 Scorecard, available less than 60 days after the end of 2008, summarizes the state of congestion in 2008 across the America and how it changed versus 2007.

Like most other aspects of society, 2008 was no ordinary year in terms of traffic or congestion, for several high profile reasons:
  • Fuel prices. 2008 brought unprecedented fuel price volatility, with a massive and consistent increase through the first half of 2008 followed by an even greater plunge in prices during the second half of 2008. Overall, average fuel costs in 2008 were up nearly 20% from 2007.
  • Unemployment. Peak hour traffic is largely associated with commuter traffic, people traveling to and from jobs. 2008 saw a steady increase in the nation’s unemployment rate, with every month being higher than the comparable month in 2007.
  • Traffic Volume. The combination of higher fuel prices and a struggling economy yielded a consistent decline in overall traffic volume. Official figures from the Federal Highway Administration (FHWA) show that the first eleven months of 2008 were substantially below 2007 levels, with percentage reductions never before recorded. Overall, FHWA reported a 3% reduction in vehicle miles traveled on the types of roads analyzed in this Scorecard.

Leveraging tens of billions of data points from 2006, 2007 and 2008 collected and archived by the INRIX Smart Dust Network, this Scorecard publishes the most up-to-date information regarding overall congestion and specific bottlenecks on the major roadways of urban America. By analyzing over 30,000 road segments on more than 47,000 miles of the major highways in the nation’s 100 largest metropolitan areas, this report informs the ongoing debate of one of the nation’s most frustrating and intractable issues: urban traffic congestion. How bad is congestion? Where is it worst? How has it changed? What can be done about it? This Scorecard provides the most comprehensive and timely national scale glimpse of the answers to these questions.


National Congestion Results and Trends

Overall, the nation’s peak period time Travel Time Index (TTI) for 2008 was 1.09. This means that during peak driving times a random traveler on a random trip on the roads analyzed took 9% extra time, on average, than if there was no congestion. This represents a decrease in the Travel Time Index of 3.5% from 2007; more than reversing the increase of 1.9% between 2007 and 2006 (See figure ES-1).

When considering the change in congestion – which is the extra amount the Travel Time Index is above 1.00 (a Travel Time Index of 1.00 would define an instance when no congestion existed and a trip was taken entirely in free flow conditions) – the decrease is even more startling: peak hour congestion on the major roads in urban America decreased nearly 30% in 2008 versus 2007.

As the details in the Scorecard highlight, other key results include:
  • National congestion was lower every hour of every day in 2008 versus 2007 – between 15% and 60% lower depending on the hour and day.
  • Friday from 5 to 6 PM remained America’s most congested hour of the week, although the Travel Time Index fell 23% from 1.26 to 1.20, just ahead of Thursday 5 to 6 PM, which had a TTI of 1.19 in 2008.
  • Wednesday saw the biggest drop in congestion, with a 31% overall decrease in peak periods.
  • Each weekday morning, peak hour congestion dropped much more than its corresponding evening peak hour congestion (See figure ES-2).
  • National congestion levels were essentially the same when comparing the first and second halves of 2008, thus it seems that higher fuel prices in early 2008 and the slower economy later in the year netted the same drop in overall congestion.
  • Congestion in off peak hours (outside of the AM and PM weekday commuting times) decreased by more than 36%, substantially outpacing the significant drop in peak hour congestion.
As expected, the health of the economy and higher average fuel costs led to decreased congestion – but the scale of the decrease, roughly 30%, is startling.
 

Metropolitan Comparisons and Trends

While no region of the country was spared volatile fuel prices and some amount of economic stress, some regions clearly have had a better or worse relative impact. Couple these differences with variations in overall highway construction and maintenance activity – a key contributor to recurring regional congestion as highlighted in later sections – and the reduction in overall congestion varied widely by metropolitan area. The 2008 Top 10 Ranking highlights the nation’s top 10 regions in terms of overall congestion, Travel Time Index (which normalizes the congestion data by road miles analyzed in each region, giving the fairest consumer-oriented view of congestion in a region), the biggest drops in Travel Time Index between 2007 and 2008, and the most congested “worst hour” rankings.

The Scorecard includes a detailed table with several different parameters than can be used to compare congestion and trends between the regions. Several highlights are included in the details of this table:
  • 99 of the 100 regions saw congestion levels decrease. Baton Rouge, LA, with a 6% increase in overall congestion, was the only region with an increase from 2007, shooting it up the metropolitan rankings from 47th to 33rd in overall congestion.
  • In almost all cases, when regions moved up a list, it was due to less congestion reduction than its peer regions in that category. For example, despite a 20% drop in congestion, the Minneapolis-St. Paul region moved from 13th to 10th in total congestion, passing Atlanta, Miami, and Philadelphia.
  • Los Angeles moved ahead of Honolulu with the highest metropolitan Travel Time Index. Honolulu’s 34% drop in congestion lowered its Travel Time Index from 1.45 to 1.31, where Los Angeles’ 23% drop lowered its TTI from 1.44 to 1.33

Bottlenecks

Nearly 31,000 individual road segments were analyzed to determine the extent and amount of average congestion each had in 2008. More than 6000 segments registered at least one hour of the week when one can expect to travel at less than half the free flow or uncongested speed. As expected based on the overall congestion data, the number and intensity of bottlenecks were down considerably from 2007. Overall 28% fewer segments had at least one hour of congestion in 2008. Figure ES-4 details the drop for each threshold.

The nation’s worst bottleneck remained the same, a westbound stretch of the Cross Bronx Expressway/I-95 leading up to and including the Bronx River Parkway exit 4B interchange. As in 2007, it was congested an astounding 94 hours of the week, but the average speed while congested rose in 2008 to 11.2 MPH from 9.8 MPH.


Conclusions

With a new presidential administration, the just-passed stimulus package, and the upcoming expiration of SAFETEA-LU, this is an important year for transportation issues. The Scorecard has generated some relevant findings to assist in both national and regional debates, including:

  • Volume changes have much bigger impacts under congested conditions. FHWA data shows that in 2008, traffic on “urban interstates” was down 3% nationwide compared to 2007. This has translated to a nearly 30% reduction in peak hour congestion and an even larger 36% drop in off-peak congestion. This illustrates multiple issues:
    • Demand management can have sizeable impact on congestion, even if total volume changes are modest. Massive increases in fuel prices had effects similar to policy initiatives under consideration such as variable pricing, managed lane strategies and better travel information. When a road network is at capacity, adding or subtracting even a single vehicle has disproportionate effects for the network. This phenomenon has been well known for a long time, but this data illustrates it in real-world terms on a nationwide basis.
    • While the drop in congestion is welcomed in general, the primary root causes – high fuel costs and lagging economic activity – are not. Ideally, the nation’s economy will turn around in short order and fuel prices will remain moderate. If so, we can expect congestion to largely snap back to levels comparable to 2007 levels or worse. While we all should cheer the reduction in congestion in 2008, we should be under no illusion that this is permanent. We must still continue to focus energies on policies and methods to tackle congestion. When the economy is growing again, congestion will likely move to the front and center again as the nation’s primary surface transportation problem.
  • The linkage between work zones and bottlenecks. The significant percentage of bottlenecks that appear to be related to work zones underscores the need to focus on managing work zones in ways that mitigate congestion. With the upcoming stimulus spending, the amount of work zones is likely to grow to numbers never before seen. Further, there is strong desire to move as quickly as possible in getting highway projects underway. Proper work zone planning will be essential if we are to keep the nation’s highways from becoming a parking lot.
  • Video (2:40 minutes): YouTube

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