Elevated Express Lanes Relief for Urban Congestion

Published November 1, 2006

Many people agree there is a need to expand urban highway capacity to restore the kind of mobility we had 20 years ago, but most throw up their hands and say, “There’s no room to add any lanes to our freeways.”

Those people should see what has happened in Tampa, Florida.

In August the Tampa-Hillsborough County Expressway Authority (THCEA) opened its new elevated express lanes.

THCEA operates the Crosstown Expressway, an east-west toll road that brings commuters to downtown Tampa from both eastern and western suburbs. As new eastern suburbs grew over the past decade, the westbound morning commute on the expressway became heavily congested.

Elevated Lanes

Although THCEA could have squeezed in one more lane in each direction, they took a longer-term view of the need for increased capacity. They came up with an innovative plan to add three express lanes, elevated above the median of the expressway.

Because traffic on this route is highly directional–westbound in the morning, eastbound in the afternoon–they made the express lanes reversible. The new lanes add three lanes of capacity to the two inbound lanes in the morning, and likewise for the outbound trip in the afternoon.

That’s a 150 percent increase in capacity.

Economical Construction

You might think that because the new lanes are elevated, they must cost a fortune, but they don’t. The overall project is nine miles long, of which 7.5 miles are elevated. The design permits three full lanes plus a breakdown lane on each side (56 feet of total width) to be supported on a single central pillar just six feet wide.

This is possible because the bridge is made of pre-cast segments that were made offsite, trucked to the construction site, and hoisted into place.

This is the most economical way yet devised to build elevated roadways. It was developed by Figg Engineering, a Florida firm that has built bridges in areas across the country.

Inexpensive, Effective

The original budget was $320 million, but due to some errors by one of the contractors involved, many of the original pillars were not properly anchored in the ground and had to be replaced, boosting the cost to $420 million.

Still, for 27 lane-miles of physical capacity, most of it elevated, that comes to only $15.5 million per lane-mile–well below what many highway engineers and DOTs have thought possible for elevated expressway construction in 2006.

I drove the elevated lanes during the morning rush-hour in mid-August, and we zipped along at the speed limit the entire way, not even having to slow down to pay the toll.

All toll collection on the elevated lanes is open-road, electronic toll collection, so there isn’t even a toll plaza–just overhead gantries that read your Sunpass transponder. There are also video cameras to nab violators.

Feasible Elsewhere

Because such elevated lanes have great potential for unclogging other freeways across the country, I asked THCEA to work with Figg Engineering to develop generic cost estimates for such projects. Here’s what they came up with:

Not including right of way (because we’re presuming the new lane would be built on pillars in the median of the existing congested expressway), the total cost is estimated at $18 million per lane-mile for a two-lane facility, $15 million per lane-mile for a three-laner, and $13.6 million per lane-mile for a four-lane elevated highway.

These are 2006 costs, reflecting today’s costs of steel, concrete, and other materials and labor.

So don’t let anyone tell you there’s no feasible way to add capacity to congested expressways. I’ve been to Tampa–I’ve seen the future, and it works.

Robert Poole ([email protected]) is director of transportation studies at the Reason Foundation and an engineering graduate of MIT.