Safety Benefits of the Proposed Transportation Plans

The proposed Thoroughfare Development Plan and Hike and Bike System Master Plan both increase safety by slowing motor vehicle speeds by not overbuilding roads to widths that cause speeding.  They also provide for street improvements that make walkers and bicyclists more visible to motorists.


The plans call for pedestrian improvements, such as more sidewalks, pedestrian crossing signals, refuge islands, raised crossings, raised medians, curb extensions and bulb outs.

Studies show that measures such as these reduce pedestrian-auto collisions by significant percentages (indicated in parentheses below)[1]:

More sidewalks (74% crash reduction)
Pedestrian countdown signal heads (25% crash reduction)
Pedestrian refuge islands (56% crash reduction)
More visible and improved crosswalks/pedestrian crossings (25% crash reduction)


“Road diets,” or “travel lane conversions,” are when a vehicle travel lane is changed to another use such as a bike lane, sidewalk, or on-street parking.

The plans call for a limited number of these “road diets.”  These 14 road segments are listed in the TDP in Table 5.2, page 25.  13 of these segments are 4 lanes to be converted to 3 lanes (2 travel lanes and a middle turn lane).  In these segments, the space taken up by the fourth lane would be converted to bike lanes on either side.

Traffic flow on these streets can improve because the addition of a middle turn lane for cars means vehicles will no longer need to stop while waiting for a car ahead of them to turn left.  Similarly, this middle turn lane can reduce collisions caused by this stop-and-go traffic.  Traffic flow is more uniform, with fewer sudden stops and starts.

Studies show that safety is increased via the addition of this middle turn lane:

  • one study finds that “the resulting benefits [of a road diet] include reduced vehicle speeds; improved mobility and access; reduced collisions and injuries; and improved livability and quality of life.”[2]
  • a Federal Highway Administration study found that car crashes were reduced by 6% after road diets were initiated.[3]
  • a study of 13 four-lane undivided to three-lane conversions showed a 60 to 70 percent reduction in the number of vehicles traveling 5 mph faster than the speed limit.  These roads all saw a reduction in total crashes that ranged between 17 and 62 percent reduction.[4]
  • a Pennsylvania DOT study found that a road diet from 4 lanes to 3 lanes (including a middle turn lane) led to reduced crashes, reduced dangerous maneuvers, more uniform traffic flow, and overall trip times were unaffected.[5]


The City of Arlington 2011 Citizen Survey showed that speeding in neighborhoods was the top concern of Arlington residents.  These plans help to reduce speeding in our community.

Source: "Focus on Priorities" - Arlington City Council Priority Planning Session, March 11, 2011


Curb extension/Bulb out

Pedestrian crash risk is reduced when pedestrians only have to cross two and three lane roads compared to roads with 4 lanes or more.  By reducing the width of the road from 4 lanes to 3 or 2 lanes, pedestrians can cross the street more easily and safely.[6]


More cyclists equals more safety:

  • The Minneapolis Star Tribune reports that a 2008 study shows that as the number of bicyclists on city streets increases, the rate of crashes with vehicles falls.  This is consistent with a 2003 study of two California cities.[7]
  • An Australian study also confirms that as the number of bicyclists increases the rate of crashes with vehicles decreases.  The study finds that motorists simply adjust their behavior.[8]
  • The risk of vehicle-pedestrian accidents decreases as the number of pedestrians along the street increases.[9]
  • A study by Peter L. Jacobson in the journal, Injury Prevention, in 2003, found similar results, studying 68 cities in California, 47 Danish towns, and other European countries.  The study found that pedestrian-vehicle accidents and bicycle-vehicle accidents decreased as the number of pedestrians and cyclists increased.[10]


These proposed plans will improve safety for all and we hope that our council-members will consider this information when voting on these plans.


[1] 2007 Federal Highway Administration Crash Reduction Factors Study (, cited in Hike and Bike Plan, page 4-5.

[2] Rosales, Jennifer, Road Diet Handbook: Setting Trends for Livable Streets (New York:  Parsons Brinckerhoff  2006), p. 3, citing in Hike and Bike Master Plan at page 3-5.

[3] Federal Highway Administration Summary Report, “Evaluation of Lane Reduction “Road Diet” Measures and Their Effects on Crashes and Injuries” March 2004,

[4] Knapp, K.K. and K.L. Giese, “Guidelines for the Conversion of Urban Four-Lane Undivided Roadways to Three-Lane Two-Way Left-Turn Lane Facilities,” Center for Transportation Research and Education, Iowa State University, Ames, IA, April 2001, cited in Mobility in Arlington, February 2011, , page 3.

[5] Burden, D. and P. Lagerwey, “Road Diets:  Fixing the Big Roads,” Walkable Communities, Inc., March 1999,

[6] Federal Highway Administration (FHWA) Summary Report, “Evaluation of Lane Reduction “Road Diet” Measures and Their Effects on Crashes and Injuries” March 2004, , citing FHWA report, “Safety Effects of Marked Versus Unmarked Crosswalks at Uncontrolled Locations, September 2006.

[7] Minneapolis Star Tribune, 2.6.2011. “As Bicycle Use Climbs, Rate of Crashes with Vehicles Falls.”

[8] Science Daily, 9.7.2008.

[9] (Study of Oakland, CA).  Safe Transportation Research and Education Center, Institute of Transportation Studies, Univ. of California-Berkeley, 4.01.2006.

[10] Jacobson, Peter L., “Safety in Numbers: More walkers and bicyclists, safer walking and bicycling,” Injury Prevention. Vol. 9, pp. 205-209. (2003). See also: Elvik, Rune, “The non-linearity of risk and the promotion of environmentally sustainable transport,” Accident Analysis and Prevention, April 2009, Vol. 41, p. 849-55.

  1. Check out “Bike Lanes: A choice, not a metaphor” on Huffington Post. It’s a short article about bike lanes in New York City by Howard Wolfson, Deputy Mayor for Communication and Public Affairs. Not only does he talk about safety, but he boldly says, “we will continue to work with community groups that seek bike lanes in their neighborhoods.”

    We need to work within the community groups in Arlington.

  2. …..A road diet is a technique in whereby a road is reduced in number of travel lanes and or effective width in order to achieve systemic improvements…… .A typical road diet technique is to reduce the number of lanes on a roadway cross-section. One of the most common applications of a road diet is to improve safety or provide space for other users in the context of two-way streets with 2 lanes in each direction.

  1. 1 Town Hall Meetings! « Bike Friendly Arlington

    […] The Plan will help create a system of bike lanes that will GIVE people CHOICES about how they get around town. It will FACILITATE bicycle and pedestrian MOVEMENT throughout Arlington without impacting vehicular movement. Bike are already allowed on the steets, but adding bike lanes will make that kind of movement SAFER. […]

  2. 2 Arlington’s Hike & Bike Master Plan Built to Completion « Bike Friendly Arlington

    […] And they continued to do so despite all the research and supporting studies presented to show the safety, health, and environmental benefits of bicycling […]

  3. 3 Reason for Support : There are Riders of Different Ability « Bike Friendly Arlington

    […] The fact of the matter is that people do not want to ride to a destination if they perceive that their ride there is too dangerous. It has been proven that adding on-street bicycling infrastructure increases ridership. Increased ridership increases safety. Which increases ridership again. Read more about that here: Safety. […]

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