AASHTO Subcommittee on Bridges and Structures Technical Committee T-8, Movable Bridges

Paul B. Fossier, Jr., P.E., M. ASCE Assistant Bridge Design Administrator Louisiana Department of Transportation & Development

The current 2007, 2nd edition of the AASHTO LRFD Movable Bridge Design Specifications:

Section 1.4.4 Safety Design – 1.4.4.1 General: ◦ Warning signs, hazard identification beacons, traffic signals, signal bells

and gongs, gates and barriers, and other safety devices shall be provided for the protection of pedestrian and vehicular traffic.

Section 1.4.4.4 Safety Design – 1.4.4.4 Traffic Gates and Barriers: ◦ Two types of gates should be provided on each approach roadway to a

movable span bridge: a warning gate and a physical barrier, i.e., resistance gate.

◦ Energy absorbing systems may be utilized for barrier gates. ◦ Gates shall be specified to operate reliably at the maximum wind

velocities for which the movable bridge is considered operational.

The following states have participated in the barrier survey and the number next to each represents the number of movable bridges.

Louisiana (147) Florida (143) Illinois (59) New Jersey (54) California (38) Michigan (24) North Carolina (17) Delaware (11) Ohio (11) Texas (8) South Carolina (7) There are 845 movable bridges in the U.S.

The pie-chart below represents the percentages of movable bridges for each state surveyed in the U.S. Total survey is 519 bridges or 61.4%.

17%

17%7%

6%

4%

3%

2% 1% 1% 1%1%Percentage of Movable Bridges

Louisiana

Florida

Illinois

New Jersey

California

Michigan

North Carolina

Delaware

Question 1: Does your state design standard, specifications or policies require a physical barrier as shown above (Yes/No)?

California and Louisiana: ◦ Required on all movable bridges.

Florida: ◦ Determined on a bridge by bridge basis. ◦ Required on bascules at rest pier side, vertical lifts, swing spans,

and (some) double bascule spans. ◦ Double bascule spans: Leaf itself serves as barrier.

New Jersey: ◦ Required on all state highway carrying movable bridges. ◦ Barrier gates extend across entire roadway.

Ohio: ◦ Physical barrier not required, but is always present because one

has always been there.

Question 2: AASHTO LRFD Movable Bridge Design Specification 1.4.4.4 does not provide guidance for design loads for the physical barrier. Does your state standards, specifications or policies indicate the design load or design specifications for the barrier design (Yes/No)? If yes, please provide a copy of the detail.

New Jersey: ◦ Requires minimum loading capacity for all new barrier gate

installations. ◦ Design to requirements of the Federal Highway

Administration (FHWA) to meet Test Level 2 (TL-2) conditions as specified in NCHRP 350.

◦ Gate must be capable of stopping a 4,410 pound vehicle traveling at 43 mph impacting the gate arm at 90 degrees.

North Carolina: ◦ Requires barrier to withstand the load of a 5,000 pound

vehicle at 50 mph. Examples: (Memorial) New Hanover County and (New

Bern) Craven County.

Question 3: Does your state have a standard detail for the physical barrier (Yes/No)? If yes, please provide a copy of the detail.

California: ◦ Standard design consists of 8”x8” posts on approximately

48” centers (to space evenly across deck and fit within bridge girders), which raise 36” out of the deck surface.

◦ The machinery is suspended under the deck structure (on a catwalk) and powered by motor driven mechanical hoist on a common shaft.

Louisiana: ◦ Standard design typically consists of 2 barrier columns and

one structural steel tube that is raised and lowered by means of a mechanical drive system. (This system is located on each side of the bridge.)

Courtesy of California Department of Transportation

Courtesy of California Department of Transportation

Courtesy of Louisiana Department of Transportation and Development

Question 4: Does your state design your own physical barrier or do you purchase a commercial/proprietary barrier?

Florida: ◦ Use Roadway/B&B traffic barriers.

New Jersey, North Carolina, Ohio, South Carolina: ◦ Use Commercial/Proprietary barriers.

California, Louisiana, Texas: ◦ All designs (in-house). ◦ California: Standard design as part of the contract plans.

Michigan: ◦ Physical barriers are no longer used.

Question 5: Has your state had vehicular accidents involving impacts into existing physical barriers (Yes/No)? If yes, please indicate how many accidents and how severe (injuries/fatalities) if data is available.

55%

9%

36%

Injuries / Fatalities Due to Impacts Into Existing Physical Barriers

InjuriesFatalitiesN/A