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Operational and Safety Impacts of Angle versus Parallel versus Back-in Parking

Research Problem Statement


There is a sizable body of literature examining the safety effects of angle and parallel parking.  What is not always evident is:


·         the context within which these findings are applicable (surroundings, traffic volumes);

·         the safety effects of back-in angle parking;

·         the safety effects of buffer spaces between through traffic lanes and parking lanes;

·         guidelines for allocating cross-section width between bicycles and parked vehicles;

·         the needed cross-section width for parallel parking; and

·         the economic effects of different parking choices.


Recent experimentation examines back-in angle parking as an alternative to head-in angle parking.  Current research in Rhode Island is examining tradeoffs between bike lane width and parking width.  The pavement marking diagrams in recent versions of the MUTCD have called for a marked parallel parking stall that is 8 feet wide; some recent design publications have specified less width.

With the emphasis in and growth of New Urbanism and Context Sensitive Design, traffic engineers need more definitive studies and explanations of the tradeoffs and affects of prohibiting or allowing various types of on-street parking arrangements.


Literature Search Summary


Curb parking was found to be directly involved in 17 to 18% of all accidents on urban streets; the rate of parking accidents per mile was eight times greater on major streets than on minor (Box 1970).  Humphreys et al. (1979) reviewed data from ten cities, finding that over 50% of non-intersection crashes involved parking.  McCoy et al. (1990) surveyed 135 miles of urban state highway with curb parking.  Data were collected from 22,572 parallel spaces and 6,314 angle spaces in a number of cities and towns.  Overall, 26% of the non-intersection accidents on major streets and 56% on two-way, two-lane streets were parking accidents.  In one study, the cost of parking accidents was found to be about half of the average (Rankin).

Edwards (2002) advocated angle parking because it provides a wider “buffer” between sidewalks and driving lanes, which helps reduce vehicle splash, noise and fumes, and helps improve the perception of safety for the pedestrian.  Many consider angle parking to be more dangerous than parallel (Rankin).  In a synthesis of a number of studies, Box (2002) found higher accident rates for angle parking than for parallel, with a few exceptions.  A Nebraska study found higher accident rates for angle parking by any measure as compared with parallel parking (McCoy et al.).  Humphreys et al. (1979) concluded the crash rate increased with land use type: the lowest being associated with residential, and increasing with multifamily, office, and retail.  The level of use rather than the parking configuration appeared to be the key to the midblock accident rate: for streets with over 600,000 parking space hours per kilometer per year, parallel parking is not safer than angle parking, given similar land uses.  Zeigler (1971) said that parking at an extremely flat 22.5O angle with the curb was proven to be quiet safe and user-friendly.



Research Objective


The objective of this research is to more fully investigate and document the effects and tradeoffs of allowing or prohibiting on-street parking. 


Task 1.      Issues to examine include:

1.  under what conditions should on-street parking be allowed or prohibited;

2.  if parking is allowed, under what conditions should it parallel, head-in angle, or back in angle;

3.  how much cross-section width should be allocated for a parked vehicle or for bicycles;

4.  what are the economic effects of these choices?


Task 2.      The project should include a literature review of previous related research.


Task 3.      The safety effects of on-street parking could be better examined using data from those locales that have improved their crash reporting processes by means such as using satellite crash location technology.  The context of studies needs to be better defined: factors such as abutting land use type and street traffic volumes should be reported, and both data and findings should be stratified by context, so that findings taken from one environment are not applied without justification to other environments.


Task 4.      A necessary component to this research will be findings from agencies that have experimented with back-in angle parking, a buffer strip between travel lanes and angle parking, and the flat-angle parking advocated by Ziegler.


Task 5.      An examination of the effects of curb parking upon business and the community would be helpful.  A confounding problem is that it is not uncommon for parking enhancements to be accompanied by other area improvements.


Estimate Of Problem Funding and Research Period


Recommended Funding: 



Research Period:  

30 months


Urgency, Payoff Potential, and Implementation


Traffic engineers in urban settings are sometimes pressured to permit on-street parking, which in some situations may be unsafe.  Findings from this study would help them evaluate specific situations and distinguish between locations where on-street parking could be allowed and those where it should be opposed.

Additional research will be of little benefit unless an effective technology transfer method to get the information into the hands of practitioners and local political leaders is employed.

Sponsoring Committee:AKD10, Performance Effects on Geometric Design
Date Posted:06/01/2007
Date Modified:06/03/2007
Index Terms:Parking, Parking facilities, Angle parking, Back-in angle parking, Parallel parking, Highway safety, Highway operations, Safety impact studies,
Cosponsoring Committees: 
Operations and Traffic Management
Safety and Human Factors
Terminals and Facilities

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