In rpm's ongoing series about highway engineering marvels, the focus thus far has been on eye-catching feats of design and construction. more

The challenge: route eight lanes of traffic beneath the soft mucky bottom of Baltimore’s harbor. The harbor is more than 100 feet deep in places, and the tunnel would have to be more than a mile long, and, oh yeah, it would have to be built on a continuous curve to avoid encroaching on a national landmark.

The elegant design of the Sunshine Skyway Bridge that carries Interstate 275 across the mouth of Tampa Bay in Florida is what makes it the focus of this month’s installment in rpm’s ongoing series of stories about Engineering Marvels.

The next time you have a chance to drive a 1940-era two-lane road, pay attention to not only the curves, but the ups and downs of the roadway. Old roadways are roller coasters, often with minimal earth moved to get the roads across gullies and over ridges.

It's ironic that the better engineers and road builders do their jobs, the less their "customers" notice their work. Bridges, tunnels and other roadway structures utilize engineering feats on par with the building of the Pyramids or the Great Wall of China, but if the structures are well-designed and well-built, drivers see only a smooth concrete roadway and maybe a few guard or bridge railings.