HIGHWAY ACCIDENT REPORT
Adopted: April 14, 1977
TRANSPORT COMPANY OF TEXAS
TRACTOR-SEMITRAILER (TANK) COLLISION
WITH BRIDGE COLUMN AND SUDDEN
DISPERSAL OF ANHYDROUS AMMONIA CARGO
I-610 AT SOUTHWEST FREEWAY,
HOUSTON, TEXAS
MAY 11, 1976

NTSB Number: HAR-77/01
NTIS Number: PB-268251 

SYNOPSIS
About 11:08 a.m., on May 11, 1976, a Transport Company of Texas tractor-semitrailer (tank) transporting 7,509 gallons of anhydrous ammonia struck and penetrated a bridge rail on a ramp connecting I-610 with the Southwest Freeway (U.S. 59) in Houston, Texas. The tractor and trailer left the ramp, struck a support column of an overpass, and fell onto the Southwest Freeway, approximately 15 feet below. The anhydrous ammonia was released from the damaged tank semitrailer.
Six persons died as a result of the accident, 78 persons were hospitalized, and approximately 100 other persons were treated for injuries.

The National Transportation Safety Board determines that the probable cause of this accident was the excessive speed of the vehicle combined with the lateral surge of liquid in the partially loaded tank truck, which caused it to overturn. The cause of 5 of the 6 fatalities and all of the 178 injuries was the inhalation of anhydrous ammonia. Contributing to the severity of the accident was the failure of the bridge rail to contain or redirect the vehicle.

Innovations in transportation of pressurized liquefied products could result in a reduction of accident severity. As a result of its investigation of another tank-semitrailer accident near Eagle Pass, Texas, on April 29, 1975, the Safety Board recommended that the Secretary of Transportation "initiate a research program to identify new approaches to reduce the injuries and damages caused by the dangerous behavior of pressurized, liquefied flammable gases released from breached tanks on bulk transport vehicles." The Department of Transportation now intends to contract for such a study, depending upon the availability of funds, sometime during FY 1977. Ammonia will be included in the study.

RECOMMENDATIONS

As a result of its investigation of this accident the National Transportation Safety Board submitted the following recommendations to the Federal Highway Administration:

"Expedite past recommendations of the Safety Board regarding the adoption of standards for bridge barrier systems that require new installations to comply with performance standards." (Class II, Priority Followup)(H-77-4)

"In consultation with State and local governments, establish highway design criteria for the selection, location, and placement of traffic barrier systems that will redirect and prevent penetration when struck by heavy vehicles. The criteria for preventing vehicle penetration should consider the human exposure to injury and the effects of hazardous cargo that could result from barrier penetration." (Class II, Priority Followup) (H-77-5)

"Develop guidelines for local and State agencies to use in designating and periodically reviewing routes for the transportation of hazardous materials as a means of reducing injury and damage from accidents involving hazardous materials in their jurisdictions." (Class II, Priority Followup) (I-77-1)

As a result of its investigation of this accident the National Transportation Safety Board reiterates the following recommendations made after previous investigations:

to the Federal Highway Administration:

"The Bureau of Motor Carrier Safety (Federal Highway Administration) in cooperation with affected industries, as represented by the Tank Truck Technical Council, conduct an investigation designed to resolve the overturn stability problems created by liquid surging of partially loaded tank-truck combinations. The ultimate objective of such a research program should be the promulgation of Federal regulations to limit the effects of surge to a specific degree. Such regulations might be based on acceptable liquid cargo outage and/or dampening requirements, consistent with safe tank-truck operations." (H-72-45)

to the U.S. Department of Transportation:

"Initiate a research program to identify new approaches to reduce the injuries and damages caused by the dangerous behavior of pressurized, liquefied flammable gases released from breached tanks on bulk transport vehicles.” (I-76-5)