Capital Beltway Crashes

1993 and 1994

U.S. Department of Transportation printed on recycled paper

National Highway Traffic Safety Administration

TRAFFIC TECH

Technology Transfer Series

Number 124 May 1996

STUDY ANALYZES CRASHES ON THE CAPITAL BELTWAY

In August 1993, a series of major crashes on the

Washington Capital Beltway focused Federal, State,

and local attention on the need to further improve

safety on this 64-mile interstate facility. More than

120 public officials from all levels of government,

concerned citizens, and safety group representatives

became active partners in developing ideas and

recommendations for action. By December 1993, 53

initiatives had been developed to improve safety on the

Beltway.

The National Highway Traffic Safety Administration

(NHTSA) sponsored six studies to better understand

how and why crashes occur on the Beltway. This roadside, on the shoulder, or at another point off

TRAFFIC TECH describes one of these studies. Preusser the main travel lanes. This type typically involves

Research Group, Inc. of Trumbull, Connecticut a single vehicle, often late at night.

examined the patterns of crashes during a two year

period - 1993 and 1994. They looked beyond the

physical characteristics of crashes to categorize driver

behavioral errors that so often cause crashes. 

In-Depth Study of Beltway Crashes 

The narrative portion of each of 4,447 Virginia and

Maryland police accident reports for Beltway crashes

were analyzed and coded into a database for the two

years of 1993 and 1994. Three types of crashes

accounted for 78 percent of all Beltway crashes, many

related to congestion problems during peak hours. No

other crash type accounted for more than 7 percent of

the crashes.

Stop-Slowing (36%) One vehicle slows or stops on crashes, with ages between 21 to 30 accounting for

the roadway and is rear-ended by some other almost one third.

vehicle. Typically, the first vehicle slows or stops

because of traffic congestion.

Ran Off Road (23%) A vehicle leaves the road

and strikes some object, or overturns, at the

Sideswipe-Cutoff (18%) One vehicle is struck in

the side by another vehicle that is changing lanes. 

Most commonly, this crash type involves a car

sideswiping another car, followed by a tractortrailer sideswiping a car, and less commonly, a car

sideswiping a tractor-trailer. Typically, sideswipecutoff is related to congestion or frequent lane

changes.

Drivers

Most drivers involved in Beltway crashes are local

residents who live in Maryland, Virginia or the

District of Columbia, not out-of-towners traveling

through the metropolitan area. Drivers between the

ages of 21 and 40 accounted for 57 percent of the

Vehicle Type

Over 9,000 vehicles were involved in the 4,447

Beltway crashes. Nearly 10 percent of these vehicles

were tractor-trailers, and nearly 6 percent were

straight trucks. These two vehicle types were

involved in 1,148 crashes, or 25 percent of the total
for the two years. There are distinct differences in the For all but one interchange, there were more Main

type of crashes for different types of vehicles. Tractor- Line crashes than either of the other two types. The

trailers were much more likely to be involved in a only exception was the Springfield interchange

sideswipe-cutoff type of crash. This type accounted (sometimes called the mixing bowl), where interstate

for almost half (46 percent) of tractor-trailer crashes. highways intersect. There, the crashes were

For cars and other nontrucks, the most frequently overwhelmingly in the On Ramp group. 

occurring crash type was stop-slowing.

Interchange Analysis

Interchanges are the most dynamic locations on the marker, and by inner or outer loop of the Beltway. 

Beltway where drivers must navigate around other Subsequent crashes that occurred within a two hour

vehicles, change lanes, merge into the main travel window of the initial crash show that up to 10 percent

lanes, and slow to exit. Beltway motorists expressed of crashes are followed by subsequent crashes. Most

concern for improving conditions at interchanges in a of these subsequent crashes occur close to the primary

series of focus groups conducted during the summer of crash, most within 5 minutes and within one-tenth of

1994. The report summarizes crashes for each of the a mile. The effect was observed to extend at least one

14 Virginia and 25 Maryland Beltway interchanges mile on the approach to the primary crash for the first

into three categories. hour. A smaller effect was also observed for up to

Main Line crashes begin with at least one vehicle

on the main line that subsequently collides with

another vehicle(s) or object within half a mile of an

interchange.

Ramp Related crashes include collisions between

one or more vehicles on the main line and one or HOW TO ORDER

more vehicles in the acceleration or deceleration

lane(s) at an interchange.

On Ramp crashes involve vehicles on the ramp

including acceleration and deceleration lanes and

collector or distribution lanes. Unlike Main Line

and Ramp Related, there is no involvement with a

vehicle on the main line. 

Crashes Causing Crashes

Another database sorted crashes by date, time, mile

one mile and up to one hour downstream of the crash.

NHTSA continues to support the Capital Beltway

Safety Team and will publish additional studies in the

near future.

For a copy of Analysis of the Capital Beltway Crash

Problem (42 pages plus appendices) write to the

Office of Program Development and Evaluation,

NHTSA, NTS-33, 400 Seventh Street, S.W.,

Washington, DC 29050, send a fax to (202) 366-

7096, or EMAIL to lcosgrove@nhtsa.dot.gov Linda

Cosgrove, Ph.D., was the contract manager for this

project.

U.S. Department 

of Transportation

National Highway 

Traffic Safety 

Administration

400 Seventh Street, S.W. NTS-33

Washington, DC 20590

TRAFFIC TECH is a publication to disseminate 

information about traffic safety programs, 

including evaluations, innovative programs, 

and new publications. Feel free to copy it as you wish. 

If you would like to receive a copy contact:

Linda Cosgrove, Ph.D., Editor, Evaluation Staff

Traffic Safety Programs

(202) 366-2759, fax (202) 366-7096

E-MAIL: lcosgrove@nhtsa.dot.gov