A New Years Diet for Our Roads

Decatur St

Decatur Street road diet at Jesse Hill Jr Drive

Earlier this week the Project for Public Spaces released a report called the “Rightsizing Streets Guide.”  The Guide provides case studies of communities around the country that improved safety, mobility, and community outcomes by reconfiguring and reducing the layout of their streets.  These new configurations have “better serve[d] the people who use them, whether they’re commuters driving, shoppers walking, or children bicycling.”  Although the Guide cites a number of excellent examples of these “road diet” projects around the country, it fails to acknowledge Atlanta’s use of this transportation strategy.

As the AJC reported in 2008, the City of Atlanta undertook a high profile road diet project on Decatur Street on the east side of the Downtown business district.  The project reduced Decatur Street from two lanes in each direction to one.  This real estate, located in the heart of Georgia State’s campus, was repurposed to widen the street’s sidewalks.  In doing so, the project provided dual benefits for this high foot traffic area: additional space for pedestrians and reducing the risk of pedestrian strikes by lowering vehicle speed. (The Guide notes that “[o]ver 80% of pedestrians hit by vehicles traveling 40 miles per hour die, compared to less than 10% that are hit at vehicles traveling 20 miles per hour.”)

The Decatur Street project is one of many road diet projects in the works for Atlanta.  The City’s comprehensive plan, Connect Atlanta, includes over a dozen road diet projects on such prominent corridors as Piedmont Road, Northside Drive, Cascade Avenue, Memorial Drive, Howell Mill Road, Bolton Road, and Boulevard.  These projects call for existing lanes to be modified to accomodate new uses like turn lanes, bicycle lanes, wider sidewalks, or traffic calming features.

The success of road diets in Atlanta and elsewhere reflects the realities of travel in urban areas.  Urban trips are typically shorter, more frequent, and more suitable for walking, bicycling, or other non-motorized options.  Right of way is limited and expensive in these areas, so transportation improvements outside of the existing real estate quickly become prohibitively expensive.  In urban areas the question is often not whether there is sufficient road capacity but whether there are sufficient non-driving options.   That second or third lane, which is used only sporadically throughout the day and encourages driving at unsafe speeds, could be more beneficial for the public as a turn lane, bike lanes, or wider sidewalks.

Traveling within compact, urban areas poses different challenges and requires different solutions than long distance travel in low desity areas.  Sometimes when we’ve binged on roadway capacity, the answer is to go on a diet.

Getting Safer, Legally

Advocates for Highway and Auto Safety's State Ratings of Driving Safety Laws

Advocates for Highway and Auto Safety’s map of state driving safety laws

The Advocates for Highway and Auto Safety have released their tenth annual “Roadmap of State Highway Safety Laws.”  The report is a nationwide survey of driving safety laws and safety data for the states.

Georgia was one of fourteen states to receive a “Green” rating, meaning it has “significantly advanced toward adopting all of the Advocates’ recommended optimal laws.” Of the fifteen laws recommended by the report, the four that Georgia has not yet adopted are:

  • Prohibiting teen drivers from obtaining a learner’s permit until they are 16;
  • Restricting teen drivers from nighttime driving;
  • Limiting the number of passengers with a teen driver without adult supervision;
  • Requiring ignition interlock devices for anyone convicted of drunk driving offenses.

According to the report’s summary of National Highway Traffic Safety Administration data, Georgia had 1,223 fatalities and 15,000 fatalities over the past decade.  The annual economic cost of motor vehicle crashes in Georgia totaled $7.85 billion.

It is striking to compare NHTSA’s estimated costs of vehicle crashes ($7.85 billion for the state) against the costs of congestion (around $2.5 billion per year for metro Atlanta, according to the Texas Transportation Institute).  Even making some generous assumptions to correct for the difference in geographic scope, it is clear that the economic cost to Georgia of vehicle crashes is far greater than that of congestion.

This data bears out the same conclusion reached by AAA earlier this year: we talk more about congestion costs but we pay more in safety costs.

Closer or Faster?

Long drives in the country and leisurely bike rides are great. But more often we walk down the street, board transit, or start the car because we need to get somewhere. In most cases, transportation is a means to an end.  But much of our analysis and discussion focuses on quality of the trip (metrics like travel time index and level of service) instead of our actual ability to reach a destination.  If the point is to get where we need to go, the salient inquiry should be accessibility rather than congestion.

This notion of accessibility has surfaced in Georgia’s recent transportation plans. Georgia’s Statewide Strategic Transportation Plan identifies the ability to reach employment centers within 45 minutes during rush hour as a key measurement for evaluating system performance. The SSTP observes that the number of workers able to reach Atlanta’s key employment centers by car shrinks by 60% during rush hour.  These smaller “employment-sheds” (the number of workers able to reach work the employment center in a given period of time) mean fewer potential employees and increased transportation costs for the employees.

The Atlanta Regional Commission’s Plan 2040 takes the “employment-shed” idea one step further and maps the 45 minute travel distance for some of the region’s key employment areas.

ARC's Modeled "Travel Sheds" Around Employment Centers Under Different Growth Scenarios

ARC’s Modeled “Employment-Sheds” Under Different Growth Scenarios

These images project that Atlanta’s employment sheds will shrink under all of the scenarios.  But they also illustrate the potential for planning and transportation investments to influence accessibility.

The traditional response to maps like these is to talk about “fixing” congestion.  Travel speeds slow during rush hour, causing the employment shed to shrink.  The reflexive response is to attempt to increase travel speeds, often by adding more capacity.  But there are other ways to improve accessibility.  Fixed guideway transit, like MARTA or light rail, runs at the same speed throughout the day so increasing the proportion of travelers using fixed guideway transit helps maintain employment sheds.

Perhaps even more important to accessibility is distance. Atlantans have among the longest average commutes in the country.  Even slight reductions in speed over these long distances can add up to dramatically longer trips and shrink employment sheds.  But changes in speed are less significant over shorter trips, so reducing the length of trips serving an employment shed helps prevent it from shrinking.

Does Accessibility Require Density or Speed?,”a report published in the Journal of the American Planning Association, considers the relative roles of distance and speed in determining an area’s accessibility.  The article considers whether our ability to reach a destination is more a function of speed or the distance of the trip.  As the study explains:

Travel to more remote shopping or work locations might be accomplished at a high speed, but the spread of these destinations can demand more travel compared to more compact and clustered urban arrangements where travel is slower.

Using data from 38 large metro regions (including Atlanta), the study considers whether accessibility is driven more by proximity or vehicle speed. And in denser areas, whether the accessibility benefits of proximity are offset by the reductions in speed.  The study concludes that proximity is the more important variable than speed and that the more compact development in urbanized areas has ten times the impact on overall accessibility than a comparable increase in vehicle speed.

Both the SSTP and Plan 2040 consider the value of proximity and recognize that reducing trip length would benefit Atlanta’s transportation system.  As the SSTP notes:

[T]he reason Metro Atlanta underperforms its peers on congestion costs per traveler is not because its congestion is necessarily more severe, but because people drive more frequently and
further under congested conditions (peak hour VMT is higher).

But politicians and the public have shown less enthusiasm for improving proximity (a planning solution) than increasing speed (an engineering solution).  Whether this reflects a preference for the quick fix, the more diffuse nature of planning decisions, or the inertia of the status quo, focusing on speed to the exclusion of proximity leaves a key strategy on the table. With our transportation funds increasingly rare and our transportation challenges on-going, it is time for proximity to take a more central role as a transportation strategy.


New Projects in the New Year

Wondering what new transit projects Salt Lake City, Denver, and Tampa plan to open in 2013? Curious what lines Phoenix, Houston, and Charlotte are building?  The Transport Politic has an excellent map and blog post detailing the status of transit projects around the country.


Atlanta is included on the map thanks to the Downtown Streetcar.  But comparing that project to the impressive, multi-year queues lined up by other cities shows the clear difference between metro Atlanta’s transit investment and that of other cities around the county.