What a congestion report doesn’t tell us about congestion

Congestion is increasing in Portland: But not, apparently, because traffic volumes are increasing

Traffic congestion reports are just as formulaic as bodice-ripping romance novels. They have a predictable narrative form: our region is growing; it has more people and more jobs and more cars. And the number of people and jobs and cars is growing (gasp!) faster than the number of lane miles of freeway and highway in the region.  The inevitable result must be greater congestion–unless we build our way out of the problem.

The Oregon Department of Transportation (ODOT) released a report earlier this week describing traffic trends on Portland area freeways. Like all such reports, its profusely illustrated with a combination of statistics and photographs showing cars, lots of cars, usually with photos taken through an extreme telephoto lens.  The report shows speeds have decreased and peak hour travel times have increased on most freeways over the past two years. It makes a big deal of the fact that the region’s employment has increased by 5.5 percent and the region’s population has increased by 3.0 percent while freeway lane-miles have increased by only 1.0 percent.

What the report doesn’t tell us is even more important than what it does say.  It does little to explain why congestion seems to be increasing, even though traffic levels are going down in many locations, and actually says very little about what we can do to reduce congestion.

Slower travel times–but less travel.

The usual story about congestion is that our roads are clogged because of an ever increasing volume of cars using them. But in this report, congestion is getting worse (travel times are increasing) even though on nearly half of the region’s freeway segments, travel is decreasing.  Its also worth noting that travel volumes are down even though the economy and population continue to grow.

The report shows that travel times are increasing on most Portland area freeways.  On Interstate 5, the major north-south route through the region, the average number of miles traveled per day has actually decreased about 6 percent from 2,778,000 in 2013 to 2,709,000 in 2015.  At the same time, afternoon peak hour travel speeds on the roadway have fallen from 36 miles per hour to 31 miles per hour in the more heavily traveled northbound direction. For I-5, the report offers no clear explanation why travel times are increasing even as traffic volumes are decreasing. The same pattern holds for I-405, where speeds are down 3 to 7 percent, even though traffic counts are down 10 to 12 percent.  In the case of of US 26 (which reaches to the region’s western suburbs, traffic counts are up in the Eastbound direction, but down in the Westbound direction.  Six of thirteen major freeway segments carried less traffic in 2015 than they did two years earlier–even though the region’s population and employment had increased noticeably.

For nearly two decades, Portland’s population and economy have grown, and per person travel has decreased. Detailed studies conducted by the regional government show that since the 1990s, average vehicle miles traveled per person have declined 20 percent and average trip lengths have decreased about 14 percent. Driving less and taking shorter trips (due to increased density and better mixing of land use types) means people are less exposed to congestion.

A flawed prescription

While packaged as a “performance report” on the region’s highways, this document is really a sales brochure for upcoming ODOT investments to widen three Portland area freeways.  The report’s press release claims:

Approval of HB 2017, the Oregon Legislature’s 2017 transportation package, provides funding for targeted safety and congestion projects that can help address the issues found in the new report.

HB 2017 provides some initial funding for three freeway projects to widen portions of I-5 in Portland, I-205 in the region’s southern suburbs, and Oregon 217 to the West. All three have been sold as “bottleneck busters.”

But when you read the detail in the report, its apparent that while wider roads and electronic signage may reduce crashes, they won’t reduce regular recurring congestion:

Let’s decipher jargon here.  “Auxiliary lane” is engineer speak for widening the freeway.  “Real Time” projects are electronic signs and modifications to ramp meters. “Improving reliability” means decreasing congestion associated with fender benders; and “safety” means fewer fender benders, not fewer injuries or deaths.  And “improve performance” doesn’t mean less congestion, it means–once again, fewer crashes.  There’s also a clear admission that these lane widenings and signals won’t eliminate congestion. So if we translate this into ordinary English, here’s what ODOT is saying:

Our plan is to widen freeways in a few spots and install more electronic signs which we hope will reduce crashes and the congestion associated with those crashes. These won’t reduce regular, daily rush hour congestion that’s not caused by crashes.  There’s actually nothing we can do about routine congestion.

In effect, ODOT is acknowledging what is now called “The Fundamental Law of Road Congestion.”  Increases in roadway capacity in dense urban environments simply induced additional travel, especially at the peak hour, with the result that congestion continues unabated. Spending tens or hundreds of millions to widen freeways in the name of reducing congestion is a futile waste of money.

Even the claim that electronic signs can reduce crashes is questionable.  The sole bit of evidence on the efficacy of the signs comes from a project ODOT implemented on Highway 217 in 2014.

The report also claims that “active transportation management”–a combination of tweaks to ramp metering and electronic traffic information and variable speed signs–added to Highway 217 were associated with a 21 percent reduction in crashes on that roadway. But the evidence for this seems conflicting.

It’s hard to square the headline claim on page 5 about Highway 217 (“TOTAL CRASHES down by 21%”) with the detail contained on the corridor report (page 49). While the Southbound lanes reported a 18 percent reduction in crashes, the Northbound lanes had a 3 percent increase.  If one combines the Northbound and Southbound data, total crashes are down 10 percent from 2013 to 2015, i.e. from 312 crashes in 2013 (121+191), to 281 crashes in 2015 (125+156), a decline of 31 crashes (281-312=31). Moreover, according to the ODOT report, some key data on travel trends in the corridor either isn’t available or is compromised because the corridor was under construction during the reporting period. ODOT’s Traffic Volume Tables data for Highway 217 (which doesn’t distinguish travel directions) reports that average daily traffic (ADT) on the northern segments of Highway 217 declined by about 10 percent between 2013 and 2015 (from 108,700 ADT to 96,400 ADT near the Sunset Highway). Traffic decreased less or increased slightly on segments further south.

If crashes are down about ten percent because traffic volumes are down as much as ten percent on certain segments of Highway 217, that’s hardly a testament to the effectiveness of the information signs.

Time losses are grossly exaggerated

Another key claim of the ODOT report is that highway congestion costs travelers 35,000 hours daily lost time, up from 28,000 hours in lost time in 2013. But, as we’ve shown before, these kinds of estimates are wildly exaggerated. First, its useful to know how ODOT computed “lost time.” According to page 18 of their report, they assumed that the “free flow” speed of Portland’s freeways was 60 miles per hour. They they treated any additional time that people spent traveling at lower speeds as “time lost” due to congestion.  Its worth noting that virtually all Portland area freeways have a 55 mile per hour speed limit, so ODOT is counting as a “cost” the inability of motorists to exceed the legal speed limit on Portland area freeways.

Second, and perhaps more importantly, there’s no feasible set of highway capacity improvement projects that could eliminate peak hour congestion. In effect, the cost of additional road capacity needed to avoid congestion would greatly exceed the value of travel time savings.

Summing up

More congestion is no doubt aggravating, but unfortunately this new ODOT report sheds little light on the problem. Despite the implication that growth is increasing congestion, its actually the case that travel volumes are down on a number of key roadways. Expanding highway capacity won’t reduce regular peak hour congestion, a fact that the report implicitly concedes, and something that has been confirmed by academic studies and real world experience. The evidence that information signs will reduce crashes and associated delay is sketchy. The report exaggerates the time lost to congestion by counting the inability to violate the speed limit as a “cost.”