James Joyner, inquiring about the I-95 tanker explosion today, asks:

How one drives a tanker truck over a barrier from an overpass, I’ll never know.

It’s actually pretty simple. The tanker apparently hit the barrier on the overpass at excessive speed, which made it crash through the barrier of the flyover ramp from the I-895 Harbour Tunnel Thruway southbound to I-95 southbound and land on the northbound lanes of I-95 below. The concrete barriers on bridges and highways, like metal guard rails, are designed to deflect vehicles back onto the roadway to avoid catastrophic crashes like this, but there’s only so much force a static barrier can deflect.

Incidentally, similar accident in 1998 in Memphis, on the one-lane ramp that connects I-40 to the north side of the Memphis 40/240 loop, claimed eight lives, and is the impetus for rebuilding the I-240/40 Midtown interchange to move the 90° turn to ground level.

Of further interest:

• Baltimore’s NBC4 has posted a collection of images from the crash.
• Microsoft TerraServer has an aerial photo of the interchange; the ramp at the top is the one the tanker fell off. I-95 is the road running SW-NE, while I-895 leaves directly to the east.