Traffic Safety Assessment

Profile of Existing Conditions

Bicycle and Traffic Volume

The Delaware Valley Regional Planning Commission (DVRPC) conducted bicycle and traffic counts in 2010 and 2011. The charts below indicate average volumes for Spring Garden between 23rd Street and Beach Street.  There is heavier eastbound vehicle traffic and heavier westbound bicycle traffic.   

SOURCE: DVRPC 2010 AND 2011

Interface Studio conducted a traffic volume analysis, showing higher overall volumes on Spring Garden Street east of 6th Street.

Image courtesy of the Pennsylvania Environmental Council. Data collected by Sam Schwartz Engineering

Speed and Crash Data

Posted speed limit signs of 25 mph are infrequent along Spring Garden.

Interface Studio prepared the following visualization of total crashes by type from 2006 to 2010.

Image courtesy of the Pennsylvania Environmental Council. Data collected by Sam Schwartz Engineering

Expected changes resulting from proposed Greenway

The Greenway may change the level of traffic safety among drivers, bicyclists and walkers. Due to the lack of consensus among researchers about the relative safety of each mode of transportation, it is difficult to predict what kind of changes to expect among various populations.

  • The Greenway design includes an alternating blocks concept, which allows dedicated left-turn lanes for vehicles at every other block. The center median avoids potential conflicts between cyclists and right-turning vehicles, which is a common conflict in the current bike lane/road configuration. However, it may also cause confusion, which may increase the potential for accidents.
  • The actual risk for any type of trip is uncertain, but there is the perceived accident risk (fear of accidents and street crime – for pedestrians) that can deter a shift to non-motorized modes. (Litman 1999)
  • Non-motorized travel is associated with lower health risk because it poses a minimal accident risk to other road users, and therefore reduces overall fatalities compared with motor vehicle driving. (Litman 1999)
  • A responsible bicyclist has a per-trip crash fatality rate about the same as of non-interstate drivers. Walking has even lower risks. (Litman 1999)
  • One study estimated the accident fatality risk for modes and found that walking is slightly more hazardous than driving, and cycling is 2.5 times more hazardous (per trip). (Litman 1999)

The Greenway’s amenities will likely attract beginner cyclists who do not currently use the Spring Garden bike lane. The increase in beginner cyclists may lead to increased bicycle injuries.

  • A Toronto Survey of bike commuters estimated that cycling has a 26-68% higher injury rate than motorized travel. (Litman 1999) The highest risk was on paths and trails with mixed uses and inexperienced users. Since the Greenway will have segregated uses, the injury rate may be assumed to be on the lower end of the 26-68% estimate.

The proposed roadway design includes traffic calming measures, such as narrowing traffic lanes from 12 feet to 10 feet. These measures may lead to a decrease in injury severity and fatalities along Spring Garden.

West of Broad Street
Image courtesy of the Pennsylvania Environmental Council

East of Broad Street
Image courtesy of the Pennsylvania Environmental Council

  • Posted speed limit signs of 25 mph are infrequent along Spring Garden. If posted speed is unknown, lane width has a greater impact on speed. (Litman 1999) So, current average speeds are likely above 25 mph, since the 12′ traffic lane width allows for higher speeds.
  • There is evidence of a relationship between lane width and the slowing of traffic speed (up to 3 mph reduction for every foot of lane narrowing).  These findings do not differentiate between the many street types, and suggests that while lane width plays a role, it alone is not responsible for this speed reduction. (Parsons Transportation Group 2003)
  • Lower speeds decrease the seriousness of injury and fatalities. Speed is one of the greatest indicators of injury severity and fatality in traffic crashes. (“Safety | Injury Severity and Impact Speed” 2011)

SOURCE: ET Braking System

 
 

SOURCE: ET Braking System

Narrowing traffic lanes may lead to an increase in specific vehicular accidents.

  • Studies show that while narrower lanes have no adverse traffic safety problem, there may be an increase in specific incidents such as side-swipes and same direction collisions. (Harwood 1990)

While Greenways can lead to an increase in certain types of accidents, the long-term benefits may offset the accident risk.

  • Non-motorized travel encourages long-term land use patterns that reduce travel distances; and active modes of transportation have significant health benefits. (Litman 1999)
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