Archives: Roads & highways

 

Dumbaugh 2005 - "Safe Streets, Livable Streets"

Dumbaugh, Eric
"Safe Streets, Livable Streets"
Journal of the American Planning Association
Summer 2001; vol.71, n.3; pp.283-300
On the Web
Relevance: low

While conventional wisdom recommends limiting roadside hazards, such as trees, and increasing lane and shoulder width will reduce the number and severity of crashes where the driver leaves the roadway, this author posits that trees and narrow lanes encourage drivers to drive more slowly and carefully, reducing the total number of crashes.

The author cites a few studies, including on in Washington on an urban/rural arterial (HWY 99?), where the presence of trees, sign supports, and other fixed objects is associated with fewer total crashes while wider lanes and shoulders are associated with more crashes. The author then conducts his own study comparing different sections of the same roadway, finding similar results.

I'd say that the numerical results in this study are a little squishy, the they and the theory are nonetheless very compelling.

 

Frank 2005 - "A Study of Land Use, Transportation, Air Quality, and Health (LUTAQH) in King County, WA: Executive Summary"

Frank, Lawrence (Lawrence Frank & Company, Inc.)
"A Study of Land Use, Transportation, Air Quality, and Health (LUTAQH) in King County, WA: Executive Summary"
September 27, 2005, Submitted to King County officials.
Relevance: high
On the Web (big pdf)

NOTE: The following summary includes only the sections of this report that deal with air quality and vehicle emissions.

The study examined per capita VOC and NOx emissions from both automobile and transit trips. It uses a variety of measures to classify urban, suburban and other land uses. Urban land uses are responsible for much lower air pollution, on a per capita basis, than suburban land uses. Interestingly, the strongest correlate to lower per capita emissions is “street connectivity.”

  • “Significantly lower estimates for NOx were generated by respondents living in areas with higher levels of retail floor area ratio, intersection density, and land use mix and residential density. Increased street connectivity where people live appeared to be the most closely associated with NOx. Mean emissions of NOx declined from 29 to 23 grams per person per day, a 26 percent reduction, between residents of the most to the least connected environments.”
  • “Significantly lower levels of VOC’s were found for respondents in areas with higher levels of floor area ratio and intersection density and residential density. Improvements to street connectivity where people lived appeared to be the most effective tool to reduce VOC’s as well. Mean emissions of VOC’s declined from 14 to 12 grams per person per day, a 7 percent reduction, for residents of the most to least connected environments.”

 

Ewing 2002 - "Measuring Sprawl and Its Impact"

Ewing, Reid; Pendall, Rolf; Chen, Don
"Measuring Sprawl and Its Impact"
Smart Growth America
2002
On the Web
Relevance: high

Ewing et al. created a sprawl index for ~83 metropolitan areas, incorporating density, land use mix, centeredness, and street accessibility. The authors also estimated the impact of sprawl on various transportation-related outcomes. They found that a higher degree of sprawl is associated with higher average vehicle ownership, daily VMT per capita, annual traffic fatality rate, and maximum ozone level; more sprawl was associated with a lower share of work trips by transit and walking. Note that, as with most sprawl studies, we can't assume a causal relationship.

More notes...

 

Retting 2003 - “A Review of Evidence-Based Traffic Engineering Measures Designed to Reduce Pedestrian-Motor Vehicle Crashes”

Retting, Richard A.; Ferguson, Susan A.; McCartt, Ann T.
“A Review of Evidence-Based Traffic Engineering Measures Designed to Reduce Pedestrian-Motor Vehicle Crashes”
American Journal of Public Health
September 2003; v.93, n.9.; pp. 1456-1463.
On the Web
Relevance: low

The authors reviewed studies on engineering measures used to reduce the risk of pedestrian injuries.  These measures were classified into speed control, separation of pedestrians from vehicles (in time and space), and increased visibility of pedestrians. Highly effective measures include:

  • single-lane roundabouts,
  • sidewalks,
  • exclusive pedestrian signal phasing that stops all traffic while pedestrians cross all ways,
  • pedestrian refuge islands, and,
  • increased intensity of roadway lighting

More notes...