Changing Speed on the Top End

GDOT is poised to make two changes to the speed limit on the top end of I-285 starting in September.  First, the default speed limit will be increased from 55 to 65 mph, to match the increased speed limit on the south side of I-285.  Second, electronic signs will be installed which allow the posted speed limit to be lowered below 65 mph when travel conditions require it.

These changes are part of the agency’s effort to improve the performance of Georgia’s interstates by better managing the system already in place.  GDOT believes the increased speed limit is necessary because a “65 mph speed is more consistent with driver behavior and conditions during time of non-congestion.” These faster drivers “creat[e] a gap in speeds when compared to those traveling at the 55 mph speed limit,” and this discrepancy leads to accidents.  However, it is unclear whether the safety benefits of synchronizing speeds outweighs the risk posed by sanctioning faster driving.

Although they were announced concurrently, raising the speed limit is a separate policy decision from the variable speed limit. The variable speed limits will allow GDOT, “in the event of an incident or heavy congestion anywhere on the Top End . . .  to reduce the speed limit approaching and in the affected area in efforts to prevent crashes and better regulate traffic flow.”

The two primary uses for variable speed limits are for weather-related conditions and congestion management:

  • Weather-Related Variable Speed Limits are used on roads where fog, ice, rain, or other factors often influence safety. When weather conditions deteriorate to the point that hazardous conditions are impending, the operating agency reduces the speed limit to one that helps minimize the likelihood of collisions.
  • Congestion-Related Variable Speed Limits are used when traffic volumes are building and congestion is likely. When volumes and/or speed exceed a predetermined threshold, the operational strategy is deployed. The intent is to handle more traffic volume at a slower, but not stop-and-go, speed.

Other states have experimented with variable speed limits and not all have been successful. Seattle saw a 13% reduction in accidents after installing variable speed limits, but St. Louis returned to fixed speed limits after the variable limits proved confusing and relatively ineffective.

“A lot of feedback we’ve done through customer surveys has said that they don’t really totally get it,” he said. “They have a lot of things on their mind, and a variable speed sign off to the side, first, do I notice it? Second, when I do notice it, do I understand what those engineers at [Missouri DOT] are trying to communicate to me?”

(Oddly, GDOT cites St. Louis as one of the cities it studied before implementing the variable speed limits.)

The two policies seem premised on fundamentally different views of how Atlanta drivers approach the posted speed limit. Raising the speed limit to 65 mph seems a concession that Atlanta drivers ignore the posted limit and choose to drive instead at the speed they see fit. In contrast, the variable speed limit assumes that drivers are not only aware of the posted speed limit but will reduce their speed to benefit travel conditions in the aggregate.  It is hard to see how the two policies can be reconciled.

Using operational changes to improve the performance of metro Atlanta’s roadways is a commendable goal, as are the accident reductions and other safety benefits the policies seek to achieve.  Only time will tell whether those benefits are realized, or whether the variable speed limit simply confuses Georgia drivers like it did those in St. Louis.

The Fast And The Dangerous

Florida Governor Rick Scott vetoed a bill last week that would have allowed the Florida Department of Transportation to raise highway speed limits by 5 mph, including going from 70 mph to 75 mph on some roads. According to the Palm Beach Post, the Governor cited safety concerns as the reason for his veto:

“Although the bill does not mandate higher speed limits, allowing for the possibility of faster driving on Florida’s roads and highways could ultimately and unacceptably increase the risk of serious accidents for Florida citizens and visitors,” Scott wrote in a veto message. “I strongly respect the opinion of state and local law enforcement officers who have contacted me to warn about the possible serious negative consequences should this bill become law. While the evidence suggests that increased driving speeds are not the sole cause of traffic accidents, they clearly contribute to the increased severity of vehicle crash outcomes in the form of needless injuries and deaths.”

In contrast, Governor Deal recently signed into law HB774 which allows the speed limit on Georgia’s urban interstates to be increased from 65 to 70 mph.

According to the Insurance Institute for Highway Safety, higher vehicle speeds makes accidents more likely and more serious.

 A 2002 study also evaluated the effects of increasing rural interstate speed limits from 65 mph to either 70 or 75 mph. States that increased speed limits to 75 mph experienced 38 percent more deaths per million vehicle miles traveled than expected — an estimated 780 more deaths. States that increased speed limits to 70 mph experienced a 35 percent increase, resulting in approximately 1,100 more deaths.

A 2009 study examining the long-term effects of the 1995 repeal of the national speed limit found a 3 percent increase in road fatalities attributable to higher speed limits on all road types, with the highest increase of 9 percent on rural interstates. The authors estimated that 12,545 deaths were attributed to increases in speed limits across the U.S. between 1995 and 2005.

This relationship between speed and road safety is both statistical and causal. The faster a vehicle is traveling, the less time a driver has to react to avoid an accident. Likewise, the faster a vehicle is traveling the more energy it has, making it harder to slow and control. As a result, higher vehicle speeds not only correlate with more accidents but are likely the cause of the increase in accidents. (Interestingly, the Senate sponsor of HB774 argued that the bill would increase public safety.)

HB774 allows GDOT to increase speed limits in urban areas, but does not require it to do so. In light of the research linking vehicle speed and accident rates, as well as Georgia’s ongoing pedestrian safety challenges, GDOT should follow Governor Scott’s lead and proceed with caution before raising the speed limits on Georgia’s roads.

Capturing Project Value

TRB’s National Cooperative Highway Research Program released a new paper, “Using the Economic Value Created by Transportation to Fund Transportation.” The acronym-laden study surveys nine value capture strategies used to link the funding of transportation projects (frequently transit projects) with the economic benefit they generate. The paper examines where and how these strategies have been used, the necessary legal framework, and their policy implications.

nchrp_syn_459 Fig 3

Strategies from National Cooperative Highway Research Program’s Value Capture Study

Many of these value capture strategies are already used in metro Atlanta. Various jurisdictions have assessed impact fees for years. MARTA continues to explore air rights and joint development proposals as part of its station-area development strategy. Both the MARTA sales tax and 2012’s failed TSPLOST referendum are variations on the sales tax district. And a primary source of the Beltline’s funding is its Tax Allocation District, the geographic unit used to implement Tax Increment Financing.

As gas tax revenues continue to decline and Congress struggles to find a reliable source of federal funding, the onus has increasingly shifted to the states and local governments to pay for transportation projects.  With local politicians no more interested in raising the gas tax than their federal colleagues, the focus has turned toward other ways to increase the transportation dollars coming in the door. Value capture strategies are politically appealing in this environment because the transportation projects are paid for by the people likely to reap their benefits.

Although metro Atlanta has already explored many of these strategies, value capture will become increasingly important as the region’s transportation needs increase and federal dollars become even more scarce.

(Update: According to the Saporta Report, MARTA intends to solicit a “request for expressions of interest” to lease the air rights over intown train stations, likely including the North Avenue, Midtown, Arts Center and Lenox stations.)